Speed chemical reactions. Definition of the concept. Factors affecting the rate of a chemical reaction: concentration of the reagent, pressure, temperature, presence of a catalyst. Law of mass action (LMA) as a fundamental law chemical kinetics. Rate constant, its physical meaning. The influence of the nature of the reactants, temperature and the presence of a catalyst on the reaction rate constant.
1. With. 102-105; 2. With. 163-166; 3. With. 196-207, p. 210-213; 4. With. 185-188; 5. With. 48-50; 6. With. 198-201; 8. With. 14-19
Homogeneous reaction rate - this is a quantity numerically equal to the change in the concentration of any reaction participant per unit time.
average speed reactions v avg in the time interval from t 1 to t 2 is determined by the relation:
Main factors influencing the rate of a homogeneous chemical reaction :
- the nature of the reacting substances;
- reagent concentration;
- pressure (if gases are involved in the reaction);
- temperature;
- presence of a catalyst.
Heterogeneous reaction rate - this is a quantity numerically equal to the change in the concentration of any reaction participant per unit time on a unit surface: .
According to the stages, chemical reactions are divided into elementary And complex. Most chemical reactions are complex processes occurring in several stages, i.e. consisting of several elementary processes.
For elementary reactions it is true law of mass action: the rate of an elementary chemical reaction at a given temperature is directly proportional to the product of the concentrations of the reacting substances in powers equal to the stoichiometric coefficients of the reaction equation.
For an elementary reaction aA + bB → ... the reaction rate, according to the law of mass action, is expressed by the relation:
wheres (A) and With (IN) - molar concentrations of reactants A And IN; a And b- corresponding stoichiometric coefficients; k – rate constant of a given reaction .
For heterogeneous reactions, the equation of the law of mass action does not include the concentrations of all reactants, but only gaseous or dissolved ones. So, for the carbon combustion reaction:
C(k) + O 2 (g) → CO 2 (g)
the velocity equation has the form .
The physical meaning of the rate constant is it is numerically equal to the rate of a chemical reaction at concentrations of reactants equal to 1 mol/dm 3.
The value of the rate constant for a homogeneous reaction depends on the nature of the reactants, temperature and catalyst.
The influence of temperature on the rate of a chemical reaction. Temperature coefficient of the rate of a chemical reaction. Active molecules. Distribution curve of molecules according to their kinetic energy. Activation energy. The ratio of activation energy and chemical bond energy in the original molecules. Transition state, or activated complex. Activation energy and thermal effect of the reaction (energy diagram). Dependence of the temperature coefficient of the reaction rate on the activation energy.
1. With. 106-108; 2. With. 166-170; 3. With. 210-217; 4. With. 188-191; 5. With. 50-51; 6. With. 202-207; 8 . With. 19-21.
As temperature increases, the rate of a chemical reaction usually increases.
The value showing how many times the reaction rate increases when the temperature increases by 10 degrees (or, what is the same, by 10 K) is called temperature coefficient of chemical reaction rate (γ):
where are the reaction rates, respectively, at temperatures T 2 and T 1 ; γ - temperature coefficient of reaction rate.
The dependence of the reaction rate on temperature is approximately determined empirically van't Hoff's rule: with every 10 degree increase in temperature, the rate of a chemical reaction increases by 2-4 times.
A more accurate description of the dependence of the reaction rate on temperature is possible within the framework of the Arrhenius activation theory. According to this theory, a chemical reaction can only occur when active particles collide. Active are called particles that have a certain, characteristic of a given reaction, energy necessary to overcome the repulsive forces that arise between the electron shells of the reacting particles.
The proportion of active particles increases with increasing temperature.
Activated complex - this is an intermediate unstable group formed during the collision of active particles and is in a state of redistribution of bonds. Reaction products are formed during the decomposition of the activated complex.
Activation energy And E A equal to the difference between the average energy of the reacting particles and the energy of the activated complex.
For most chemical reactions, the activation energy is less than the dissociation energy of the weakest bond in the molecules of the reacting substances.
In activation theory, the influence temperature on the rate of a chemical reaction is described by the Arrhenius equation for the rate constant of a chemical reaction:
Where A– constant factor, independent of temperature, determined by the nature of the reacting substances; e- the base of the natural logarithm; E a – activation energy; R– molar gas constant.
As follows from the Arrhenius equation, the lower the activation energy, the greater the reaction rate constant. Even a slight decrease in activation energy (for example, when adding a catalyst) leads to a noticeable increase in the reaction rate.
According to the Arrhenius equation, an increase in temperature leads to an increase in the rate constant of a chemical reaction. The larger the value E and, the more noticeable the effect of temperature on the reaction rate and, therefore, the greater the temperature coefficient of the reaction rate.
The influence of a catalyst on the rate of a chemical reaction. Homogeneous and heterogeneous catalysis. Elements of the theory of homogeneous catalysis. Theory of intermediate compounds. Elements of the theory of heterogeneous catalysis. Active centers and their role in heterogeneous catalysis. The concept of adsorption. The influence of a catalyst on the activation energy of a chemical reaction. Catalysis in nature, industry, technology. Biochemical catalysis. Enzymes.
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Catalysis called a change in the rate of a chemical reaction under the influence of substances, the quantity and nature of which after completion of the reaction remain the same as before the reaction.
Catalyst - This is a substance that changes the rate of a chemical reaction and remains chemically unchanged after it.
Positive catalyst speeds up the reaction; negative catalyst, or inhibitor, slows down the reaction.
In most cases, the effect of a catalyst is explained by the fact that it reduces the activation energy of a reaction. Each of the intermediate processes involving a catalyst occurs with a lower activation energy than a non-catalyzed reaction.
At homogeneous catalysis the catalyst and reactants form one phase (solution). At heterogeneous catalysis the catalyst (usually a solid) and the reactants are in different phases.
During homogeneous catalysis, the catalyst forms an intermediate compound with the reagent, with high speed reacting with a second reagent or rapidly decomposing to release a reaction product.
An example of homogeneous catalysis: the oxidation of sulfur(IV) oxide to sulfur(VI) oxide with oxygen using the nitrous method for producing sulfuric acid (here the catalyst is nitrogen(II) oxide, which easily reacts with oxygen).
In heterogeneous catalysis, the reaction occurs on the surface of the catalyst. The initial stages are the diffusion of reagent particles to the catalyst and their adsorption(i.e. absorption) by the catalyst surface. The reagent molecules interact with atoms or groups of atoms located on the surface of the catalyst, forming intermediate surface connections. The redistribution of electron density that occurs in such intermediate compounds leads to the formation of new substances that are desorbed, i.e., are removed from the surface.
The process of formation of intermediate surface compounds occurs on active centers catalyst - on surface areas characterized by a special distribution of electron density.
An example of heterogeneous catalysis: oxidation of sulfur(IV) oxide to sulfur(VI) oxide with oxygen using the contact method for producing sulfuric acid (here the catalyst can be vanadium(V) oxide with additives).
Examples of catalytic processes in industry and technology: ammonia synthesis, synthesis of nitric and sulfuric acids, cracking and reforming of oil, afterburning of products of incomplete combustion of gasoline in cars, etc.
Examples of catalytic processes in nature are numerous, since most biochemical reactions- chemical reactions occurring in living organisms - are among catalytic reactions. The catalysts for such reactions are protein substances called enzymes. There are about 30 thousand enzymes in the human body, each of which catalyzes the passage of only one process or one type of process (for example, salivary ptyalin catalyzes the conversion of starch into sugar).
Chemical balance. Reversible and irreversible chemical reactions. State of chemical equilibrium. Chemical equilibrium constant. Factors that determine the value of the equilibrium constant: the nature of the reactants and temperature. Shift in chemical equilibrium. The influence of changes in concentration, pressure and temperature on the position of chemical equilibrium.
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Chemical reactions, as a result of which starting substances are completely converted into reaction products, are called irreversible. Reactions occurring simultaneously in two opposite directions(direct and reverse) are calledreversible.
In reversible reactions, the state of the system in which the rates of the forward and reverse reactions are equal () is called state of chemical equilibrium. Chemical equilibrium is dynamic, i.e. its establishment does not mean the cessation of the reaction. In the general case, for any reversible reaction aA + bB ↔ dD + eE, regardless of its mechanism, the following relation holds:
At established equilibrium, the product of the concentrations of reaction products divided by the product of the concentrations of the starting substances for a given reaction at a given temperature is a constant value called equilibrium constant(TO).
The value of the equilibrium constant depends on the nature of the reactants and temperature, but does not depend on the concentrations of the components of the equilibrium mixture.
A change in the conditions (temperature, pressure, concentration) under which the system is in a state of chemical equilibrium () causes an imbalance. As a result of unequal changes in the rates of forward and reverse reactions (), over time, a new chemical equilibrium () is established in the system, corresponding to new conditions. The transition from one equilibrium state to another is called a shift, or displacement, of the equilibrium position.
If, during the transition from one equilibrium state to another, the concentrations of substances written on the right side of the reaction equation increase, they say that balance shifts to the right. If, during the transition from one equilibrium state to another, the concentrations of substances written on the left side of the reaction equation increase, they say that balance shifts to the left.
The direction of the shift in chemical equilibrium as a result of changes in external conditions is determined Le Chatelier's principle: If an external influence is exerted on a system in a state of chemical equilibrium, then it will favor the occurrence of whichever of the two opposite processes weakens this influence.
According to Le Chatelier's principle,
An increase in the concentration of the component written on the left side of the equation leads to a shift of equilibrium to the right; an increase in the concentration of the component written on the right side of the equation leads to a shift of equilibrium to the left;
When the temperature increases, the equilibrium shifts towards the endothermic reaction, and when the temperature decreases, towards the exothermic reaction;
As the pressure increases, the equilibrium shifts towards a reaction that reduces the number of molecules of gaseous substances in the system, and as the pressure decreases, towards a reaction that increases the number of molecules of gaseous substances.
Photochemical and chain reactions. Features of the course of photochemical reactions. Photochemical reactions and Live nature. Unbranched and branched chemical reactions (using the example of reactions of the formation of hydrogen chloride and water from simple substances). Conditions for the initiation and termination of chains.
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Photochemical reactions - These are reactions that take place under the influence of light. A photochemical reaction occurs if the reagent absorbs radiation quanta characterized by an energy quite specific for a given reaction.
In the case of some photochemical reactions, absorbing energy, the molecules of the reagent pass into an excited state, i.e. become active.
In other cases, a photochemical reaction occurs if quanta of such high energy are absorbed that chemical bonds break and dissociation of molecules into atoms or groups of atoms occurs.
The greater the irradiation intensity, the greater the speed of the photochemical reaction.
An example of a photochemical reaction in living nature: photosynthesis, i.e. the formation of organic cell substances by organisms due to light energy. In most organisms, photosynthesis occurs with the participation of chlorophyll; In the case of higher plants, photosynthesis is summarized by the equation:
CO 2 + H 2 O organic matter+ O 2
The functioning of vision is also based on photochemical processes.
Chain reaction - reaction, which is a chain of elementary acts of interaction, and the possibility of each act of interaction depends on the success of the previous act.
Stages chain reaction:
The birth of a chain
Chain development,
Circuit break.
The initiation of a chain occurs when, due to an external source of energy (quanta of electromagnetic radiation, heating, electrical discharge), active particles with unpaired electrons (atoms, free radicals) are formed.
During the development of the chain, radicals interact with the original molecules, and new radicals are formed in each act of interaction.
Chain termination occurs when two radicals collide and transfer the energy released in the process to a third body (a molecule resistant to decay or the wall of a vessel). The chain can also terminate if a low-active radical is formed.
Two types chain reactions: unbranched and branched.
IN unbranched In reactions at the stage of chain development, one new radical is formed from one reacting radical.
IN branched In reactions at the stage of chain development, more than one new radical is formed from one reacting radical.
6. Factors that determine the direction of a chemical reaction. Elements chemical thermodynamics. Concepts: phase, system, environment, macro- and microstates. Basic thermodynamic characteristics. Internal energy of the system and its change during chemical transformations. Enthalpy. The relationship between enthalpy and internal energy of a system. Standard enthalpy of a substance. Changes in enthalpy in systems during chemical transformations. Thermal effect (enthalpy) of a chemical reaction. Exo- and endothermic processes.
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Thermodynamics studies the patterns of energy exchange between the system and the external environment, the possibility, direction and limits of the spontaneous occurrence of chemical processes.
Thermodynamic system(or simply system) – a body or group of interacting bodies mentally identified in space. The rest of the space outside the system is called environment (or simply environment). The system is separated from the environment by a real or imaginary surface .
Homogeneous system consists of one phase, heterogeneous system– of two or more phases.
PhaseA –this is part of the system, homogeneous at all its points along chemical composition and properties and separated from other phases of the system by an interface.
State system is characterized by the totality of its physical and chemical properties. Macrostate is determined by the averaged parameters of the entire set of particles in the system, and microstate- parameters of each individual particle.
Independent variables that determine the macrostate of the system are called thermodynamic variables, or state parameters. Temperature is usually chosen as the state parameters T, pressure R, volume V, chemical quantity n, concentration With etc.
Physical quantity, the value of which depends only on the parameters of the state and does not depend on the path of transition to this state, is called state function. The functions of the state are, in particular:
U- internal energy;
N- enthalpy;
S- entropy;
G- Gibbs energy (or free energy, or isobaric-isothermal potential).
Internal energy of the system U – this is its total energy, consisting of the kinetic and potential energy of all particles of the system (molecules, atoms, nuclei, electrons) without taking into account the kinetic and potential energy of the system as a whole. Since it is impossible to fully take into account all these components, when studying the thermodynamics of the system, we consider change its internal energy during transition from one state ( U 1) to another ( U 2):
U 1 U 2 DU = U 2 - U 1
The change in the internal energy of the system can be determined experimentally.
The system can exchange energy (heat Q) with the environment and do work A, or, conversely, work can be done on the system. According to first law of thermodynamics, which is a consequence of the law of conservation of energy, the heat received by the system can only be used to increase the internal energy of the system and to perform work by the system:
In the future, we will consider the properties of such systems that are not affected by any forces other than external pressure forces.
If the process in the system occurs at a constant volume (i.e., there is no work against external pressure forces), then A = 0. Then thermal effectprocess occurring at constant volume, Q v is equal to the change in the internal energy of the system:
Q v = ΔU
Most chemical reactions encountered in everyday life occur at constant pressure ( isobaric processes). If no forces other than constant external pressure act on the system, then:
A = p(V 2 -V 1) = pDV
Therefore, in our case ( R= const):
Q р = U 2 – U 1 + p(V 2 - V 1), whence
Q p = (U 2 + pV 2) - (U 1 + pV 1)
Function U+pV, called enthalpy; it is designated by the letter N . Enthalpy is a function of state and has the dimension of energy (J).
Q p = H 2 - H 1 = DH
Thermal effect of reaction at constant pressure and temperature T is equal to the change in enthalpy of the system during the reaction. It depends on the nature of the reagents and products, their physical condition, conditions ( T,r) the reaction, as well as the amount of substances involved in the reaction.
Enthalpy of reactioncall the change in enthalpy of a system in which reactants interact in quantities equal to the stoichiometric coefficients of the reaction equation.
The enthalpy of the reaction is called standard, if the reactants and reaction products are in standard states.
The standard states are:
For solids - individual crystalline substance at 101.32 kPa,
For a liquid substance - an individual liquid substance at 101.32 kPa,
For a gaseous substance - gas at a partial pressure of 101.32 kPa,
For a solute, a substance in solution with a molality of 1 mol/kg, and the solution is assumed to have the properties of an infinitely dilute solution.
The standard enthalpy of the reaction of formation of 1 mole of a given substance from simple substances is called standard enthalpy of formation of this substance.
Example entry: D f H o 298(CO 2) = -393.5 kJ/mol.
The standard enthalpy of formation of a simple substance located in the most stable (for given p and T) state of aggregation is taken equal to 0. If an element forms several allotropic modifications, then only the most stable one has a zero standard enthalpy of formation (for given R And T) modification.
Typically thermodynamic quantities are determined at standard conditions:
R= 101.32 kPa and T= 298 K (25 o C).
Chemical equations that specify enthalpy changes (heat effects of reactions) are called thermochemical equations. In the literature you can find two forms of writing thermochemical equations.
Thermodynamic form of writing the thermochemical equation:
C (graphite) + O 2 (g) ® CO 2 (g); DH o 298= -393.5 kJ
Thermochemical form of writing the thermochemical equation of the same process:
C (graphite) + O 2 (g) ® CO 2 (g) + 393.5 kJ.
In thermodynamics, the thermal effects of processes are considered from the standpoint of the system, therefore, if the system releases heat, then Q<0, а энтальпия системы уменьшается (ΔH< 0).
In classical thermochemistry, thermal effects are considered from the environmental perspective, therefore, if a system releases heat, then it is assumed that Q>0.
Exothermic is a process that occurs with the release of heat (ΔH<0).
Endothermic is a process that occurs with heat absorption (ΔH>0).
The basic law of thermochemistry is Hess's law: the thermal effect of the reaction is determined only by the initial and final states of the system and does not depend on the path of transition of the system from one state to another.
Corollary of Hess's law : the standard thermal effect of a reaction is equal to the sum of the standard heats of formation of reaction products minus the sum of the standard heats of formation of starting substances, taking into account stoichiometric coefficients:
DН about 298 (r-tions) = åD f Н about 298 (cont.) – åD f Н about 298 (original)
7. The concept of entropy. Changes in entropy during phase transformations and chemical processes. The concept of the isobaric-isothermal potential of the system (Gibbs energy, free energy). The relationship between the magnitude of the change in the Gibbs energy and the magnitude of the change in enthalpy and entropy of the reaction (basic thermodynamic relationship). Thermodynamic analysis of the possibility and conditions of chemical reactions. Features of the flow of chemical processes in living organisms.
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Entropy S- this is a quantity proportional to the logarithm of the number of equally probable microstates through which a given macrostate can be realized:
The unit of entropy is J/mol·K.
Entropy is a quantitative measure of the degree of disorder of a system.
Entropy increases during the transition of a substance from a crystalline state to a liquid and from a liquid to a gaseous state, during the dissolution of crystals, during the expansion of gases, during chemical interactions leading to an increase in the number of particles, and especially particles in the gaseous state. On the contrary, all processes as a result of which the order of the system increases (condensation, polymerization, compression, reduction in the number of particles) are accompanied by a decrease in entropy.
There are methods for calculating the absolute value of the entropy of a substance, therefore the tables of thermodynamic characteristics of individual substances provide data for S 0, and not for Δ S 0.
The standard entropy of a simple substance, in contrast to the enthalpy of formation of a simple substance, is not zero.
For entropy, a statement similar to that discussed above for DH: the change in the entropy of a system as a result of a chemical reaction (DS) is equal to the sum of the entropies of the reaction products minus the sum of the entropies of the starting substances. As with the calculation of enthalpy, the summation is carried out taking into account the stoichiometric coefficients.
The direction in which a chemical reaction spontaneously occurs is determined by the combined action of two factors: 1) the tendency for the system to transition to a state with the lowest internal energy (in the case of isobaric processes-with the lowest enthalpy); 2) a tendency to achieve the most probable state, i.e. a state that can be realized in the largest number of equally probable ways (microstates):
Δ H → min,Δ S → max
The state function, which simultaneously reflects the influence of both of the above-mentioned trends on the direction of the flow of chemical processes, is Gibbs energy (free energy , or isobaric-isothermal potential) , related to enthalpy and entropy by the relation
G = H - TS,
Where T- absolute temperature.
As can be seen, the Gibbs energy has the same dimension as enthalpy and is therefore usually expressed in J or kJ.
For isobaric-isothermal processes, (i.e. processes occurring at constant temperature and pressure), the change in Gibbs energy is equal to:
As in case D H and D S, Gibbs energy change D G as a result of a chemical reaction(Gibbs energy of reaction) equal to the sum of the Gibbs energies of the formation of reaction products minus the sum of the Gibbs energies of the formation of the starting substances; the summation is made taking into account the number of moles of substances participating in the reaction.
The Gibbs energy of formation of a substance is referred to 1 mole of this substance and is usually expressed in kJ/mol; while D G 0 of the formation of the most stable modification of a simple substance is taken equal to zero.
At constant temperature and pressure, chemical reactions can spontaneously proceed only in a direction in which the Gibbs energy of the system decreases ( D G<0).This is a condition for the fundamental possibility of carrying out this process.
The table below shows the possibility and conditions for the reaction to occur with various combinations of signs D N and D S.
By sign D G one can judge the possibility (impossibility) spontaneous flow individual process. If you put pressure on the system impact, then it is possible to carry out a transition from one substance to another, characterized by an increase in free energy (D G>0). For example, in the cells of living organisms reactions occur to form complex organic compounds; The driving force behind such processes is solar radiation and oxidation reactions in the cell.
Lecture 1 Chemical thermodynamics. Chemical kinetics and catalysis PLAN 1. Basic concepts of thermodynamics. 2. Thermochemistry. 3. Chemical equilibrium. 4. Rate of chemical reactions. 5. The influence of temperature on the rate of reactions. 6. The phenomenon of catalysis. Prepared by: Ph.D., Associate Professor. Ivanets L.M., as. Kozachok S.S. Lecturer assistant of the department of pharmaceutical chemistry Kozachok Solomeya Stepanovna
Thermodynamics – Thermodynamics is a branch of physics that studies mutual transformations various types energy associated with the transition of energy in the form of heat and work. The great practical significance of thermodynamics is that it allows one to calculate the thermal effects of a reaction, to indicate in advance the possibility or impossibility of carrying out a reaction, as well as the conditions for its occurrence.
Internal energy Internal energy is the kinetic energy of all particles of the system (molecules, atoms, electrons) and the potential energy of their interactions, in addition to the kinetic and potential energy of the system as a whole. Internal energy is a function of state, i.e. its change is determined by the given initial and final states of the system and does not depend on the process path: U = U 2 – U 1
The first law of thermodynamics Energy does not disappear without a trace and does not arise from nothing, but only passes from one type to another in equivalent quantities. A perpetual motion machine of the first kind, that is, a periodically operating machine that produces work without wasting energy, is impossible. Q = U + W In any isolated system, the total energy supply remains unchanged. Q = U + W
The thermal effect of a chemical reaction at constant V or p does not depend on the path of the reaction, but is determined by the nature and state of the starting materials and reaction products. Hess's Law H 1 H 2 H 3 H 4 Starting substances, reaction products H 1 = H 2 + H 3 + H 4 H 1 = H 2 + H 3 + H 4
The second law of thermodynamics, like the first, is the result of centuries of human experience. There are different formulations of the second law, but they all determine the direction of spontaneous processes: 1. Heat cannot spontaneously transfer from a cold body to a hot one (Clausius’s postulate). 2. A process whose only result is the conversion of heat into work is impossible (Thomson's postulate). 3. It is impossible to build a periodic machine that only cools the thermal reservoir and does work (Planck’s first postulate). 4. Any form of energy can be completely converted into heat, but heat is only partially converted into other types of energy (Planck’s second postulate).
Entropy is a thermodynamic function of state, therefore its change does not depend on the path of the process, but is determined only by the initial and final states of the system. then S 2 - S 1 = ΔS = S 2 - S 1 = ΔS = Physical meaning entropy is the amount of bound energy, which is related to one degree: in isolated systems, the direction of the flow of spontaneous processes is determined by the change in entropy.
Characteristic functions U – function of the isochoric-isentropic process: dU = TdS – pdV. For an arbitrary process: U 0 Н – function of an isobaric-isentropic process: dН = TdS + Vdp For an arbitrary process: Н 0 S – function of an isolated system For an arbitrary process: S 0 For an arbitrary process: S 0 F – function of an isochoric-isothermal process dF = dU – TdS. For an arbitrary process: F 0 G – function of an isobaric-isothermal process: dG = dH- TdS For an arbitrary process: G 0
Classification of chemical reactions according to the number of stages Simple ones proceed in one elementary chemical act Complex ones proceed in several stages Reverse reaction A B Reverse reaction: A B Parallel: B A C Sequential: ABC Conjugate: A D Conjugate: A D C B E B E
The influence of temperature on the rate of reactions The influence of temperature on the rate of enzymatic reactions t t
Van't Hoff comparison: Calculation of the shelf life of drugs using the Van't Hoff "accelerated aging" method: at t 2 t 1 Temperature rate coefficient:
Transcript
1 4. Chemical process. Why and how do chemical reactions occur? Thermodynamics and kinetics In the first half of the 19th century, a need arose to improve heat engines that produce mechanical work through chemical combustion reactions. Such heat engines at that time were firearms and steam engines. As a result, thermodynamics or the mechanical theory of heat was created in the mid-19th century. The term thermodynamics “thermodynamics” was proposed in 1851 by the English scientist William Thomson (Lord Kelvin from 1892) (). The German explorer Rudolf Julius Emanuel Clausius () called the new science Mechanische Warmetheorie "mechanical theory of heat." Modern definition: Chemical thermodynamics is the science of the dependence of the direction and limits of transformations of substances on the conditions in which these substances are found. Unlike other sections physical chemistry(structure of matter and chemical kinetics), chemical thermodynamics can be applied without knowing anything about the structure of matter. Such a description requires significantly less initial data. A specific object of thermodynamic research is called a thermodynamic system or simply a system isolated from the surrounding world by real or imaginary surfaces. A system can be a gas in a vessel, a solution of reagents in a flask, a crystal of a substance, or even a mentally isolated part of these objects. Based on the levels of interaction with the environment, thermodynamic systems are usually divided into: open systems that exchange matter and energy with the environment (for example, living objects); closed exchange only energy (for example, a reaction in a closed or refluxed flask), the most common object of chemical thermodynamics; isolated ones do not exchange either matter or energy and maintain a constant volume (approximation of the reaction in a thermostat). Rigorous thermodynamic consideration is only possible for isolated systems that do not exist in the real world. At the same time, thermodynamics can quite accurately describe closed and even open systems. In order for a system to be described thermodynamically, it must consist of large number particles comparable to Avogadro's number and thus comply with the laws of statistics. The properties of the system are divided into extensive (summing), for example, total volume, mass, and intensive (leveling) pressure, temperature, concentration, etc. The most important thermodynamic functions for calculating the state function are those whose values depend only on the state of the system and do not depend on the transition path between states. A process in thermodynamics is not the development of an event over time, but a sequence of equilibrium states of a system leading from the initial set of thermodynamic variables to the final one. Thermodynamics allows us to completely solve the problem if the process under study is generally described by a set of equilibrium stages. eleven
2 In thermodynamic calculations, numerical data (tabular) on the thermodynamic properties of substances are used. Even small sets of such data allow the calculation of many different processes. To calculate the equilibrium composition of a system, it is not necessary to write down equations for possible chemical reactions; it is enough to take into account all the substances that can, in principle, constitute an equilibrium mixture. Thus, chemical thermodynamics does not provide a purely computational (non-empirical) answer to the question why? and especially how? ; it solves problems according to the principle if..., then.... For thermal calculations, the most important is the first law of thermodynamics, one of the forms of the law of conservation of energy. His formulations: Energy is neither created nor destroyed. A perpetual motion machine (perpetuum mobile) of the first kind is impossible. In any isolated system, the total amount of energy is constant. For the first time, the connection between chemical reactions and mechanical energy was discovered by Yu.R. Mayer (1842) [1], the mechanical equivalent of heat was measured by J.P. Joule (). For thermochemical calculations, the law of conservation of energy is used in the formulation of G.I. Hess: “When any chemical compound is formed, the same amount of heat is always released, regardless of whether the formation of this compound occurs directly or indirectly and in several stages." Hess announced this law of “constancy of heat amounts” in a report at a conference Russian Academy Sciences March 27, 1840 [2] Modern formulation: “The thermal effect of a reaction depends only on the initial and final state of substances and does not depend on the intermediate stages of the process.” Enthalpy In the general case, the work done by a chemical reaction at constant pressure consists of a change in internal energy and the work of expansion of the resulting gas: ΔQ p = ΔU + pδv For most chemical reactions carried out in open vessels, it is convenient to use the state function, the increment of which is equal to the heat received by the system in an isobaric (i.e., running at constant pressure) process. This function is called enthalpy (from the Greek enthalpy heat) [3]: ΔQ p = ΔH = ΔU + pδv Another definition: the difference in enthalpies in two states of the system is equal to the thermal effect of an isobaric process. 1. In 1840, the German doctor Julius Robert Mayer () worked as a ship's doctor on a voyage from Europe to Java. He noticed that venous blood in the tropics is lighter than in Germany, and concluded that in the tropics less oxygen is needed to maintain the same body temperature. Consequently, heat and work can be mutually converted. In 1842, Mayer theoretically estimated the mechanical equivalent of heat at 365 kgm (modern 427 kgm) 2 Trifonov D.N. “Character is direct and noble” (To the 200th anniversary of Hermann Ivanovich Hess) 3. The name enthalpy was proposed by the Dutch physicist Heike Kamerlingh-Onnes (). 12
3 It is enthalpy that has proven convenient for describing the operation of both steam engines and firearms, since in both cases the expansion of hot gases or water vapor is used. There are extensive tables containing data on the standard enthalpies of formation of substances ΔH o 298. The indices mean that for chemical compounds the enthalpies of formation of 1 mole of them from simple substances taken in the most stable modification at 1 atm (1. Pa or 760 mm Hg) and 298.15 K (25 o C) are given. When it comes to ions in solution, the standard concentration is 1 mol/L. For the simple substances themselves, the enthalpy of formation is assumed to be 0 (except for white phosphorus, which is not the most stable, but the most reproducible form of phosphorus). The sign of enthalpy is determined from the point of view of the system itself: when heat is released, the change in enthalpy is negative, when heat is absorbed, the change in enthalpy is positive. An example of a thermochemical calculation of an extremely complex reaction: The enthalpy of formation of glucose from carbon dioxide and water cannot be determined by direct experiment; it is impossible to obtain glucose from simple substances. But we can calculate the enthalpies of these processes. 6 C + 6 H O 2 = C 6 H 12 O 6 (ΔH x -?) Such a reaction is impossible 6 CO H 2 O = C 6 H 12 O O 2 (ΔH y -?) the reaction occurs in green leaves, but together with others processes Let's find ΔH x algebraically. Using Hess's law, it is enough to combine three combustion equations: 1) C + O 2 = CO 2 ΔH 1 = -394 kJ 2) H 2 + 1/2 O 2 = H 2 O (steam) ΔH 2 = -242 kJ 3) C 6 H 12 O O 2 = 6 CO H 2 O ΔH 3 = kJ We add the equations “in a column”, multiplying the 1st and 2nd by 6 and “unfolding” the third, then: 1) 6 C + 6 O 2 = 6 CO 2 ΔH 1 = 6(-394) kJ 2) 6 H O 2 = 6 H 2 O (steam) ΔH 2 = 6(-242) kJ 3) 6 CO H 2 O = C 6 H 12 O O 2 ΔH 3 = kJ When calculating enthalpy, we take into account that when “turning” equation 3, it changed sign: ΔH x = 6 ΔH ΔH 2 - ΔH 3 = 6(-394) + 6(-242) -(-2816) = kJ/mol Obviously , that ΔH y corresponds to the reverse process of photosynthesis, i.e. burning of glucose. Then ΔH y = -ΔH 3 = kJ No data on the structure of glucose was used in the solution; the mechanism of its combustion was also not considered. Problem Determine the enthalpy of production of 1 mole of ozone O 3 from oxygen, if it is known that the combustion of 1 mole of oxygen in excess hydrogen releases 484 kJ, and the combustion of 1 mole of ozone in excess hydrogen releases 870 kJ Second law of thermodynamics. Entropy The second law of thermodynamics according to W. Thomson (1851): a process is impossible in nature, the only result of which would be mechanical work done by cooling the heat reservoir. 13
4 Formulation by R. Clausius (1850): heat by itself cannot move from a colder body to a warmer one or: it is impossible to construct a machine that, acting through circular process, will only transfer heat from a colder body to a warmer one. The earliest formulation of the second law of thermodynamics appeared earlier than first law, based on the work done in France by S. Carnot (1824) and its mathematical interpretation by E. Clapeyron (1834) as the efficiency of an ideal heat engine: efficiency = (T 1 - T 2)/T 1 Carnot and Clapeyron formulated the law of conservation of caloric weightless indestructible liquid, the content of which determines body temperature. The theory of caloric dominated in thermodynamics until the middle of the 19th century, while the laws and relationships derived on the basis of ideas about caloric turned out to be valid within the framework of the molecular-kinetic theory of heat. To find out the reasons for the occurrence of spontaneous processes that occur without the release of heat, it became necessary to describe heat by the method of generalized forces, similar to any mechanical work (A), through a generalized force (F) and a generalized coordinate (in this case, thermal) [4]: da = Fdx For thermal reversible processes we obtain: dq = TdS I.e. Initially, entropy S is the thermal coordinate of the state, which was introduced (Rudolph Clausius, 1865) to standardize the mathematical apparatus of thermodynamics. Then for an isolated system, where dq = 0, we obtain: In a spontaneous process ΔS > 0 In an equilibrium process ΔS = 0 In a non-spontaneous process ΔS< 0 В общем случае энтропия изолированной системы или увеличивается, или остается постоянной: ΔS 0 Энтропия свойство системы в целом, а не отдельной частицы. В 1872 г. Л.Больцман [ 5 ] предложил статистическую формулировку второго закона термодинамики: изолированная система эволюционирует преимущественно в направлении большей термодинамическоой вероятности. В 1900 г. М.Планк вывел уравнение для статистического расчета энтропии: S = k b lnw W число различных состояний системы, доступное ей при данных условиях, или термодинамическая вероятность макросостояния системы. k b = R/N A = 1, эрг/град постоянная Больцмана 4. Полторак О.М., Термодинамика в физической химии. Учеб. для хим. и хим-технол. спец. вузов, М.: Высш. шк., с., стр Больцман Людвиг (Boltzmann, Ludwig) (), австрийский физик. Установил фундаментальное соотношение между энтропией физической системы и вероятностью ее состояния, доказал статистический характер II начала термодинамики Современный биограф Людвига Больцмана физик Карло Черчиньяни пишет: Только хорошо поняв второе начало термодинамики, можно ответить на вопрос, почему вообще возможна жизнь. В 1906 г. Больцман покончил с собой, поскольку обманулся в любви; он посвятил свою жизнь атомной теории, но любовь его осталась без взаимности, потому что современники не могли понять масштаб его картины мира 14
5 It should always be remembered that the second law of thermodynamics is not absolute; it loses its meaning for systems containing a small number of particles and for systems on a cosmic scale. The second law, especially in its statistical formulation, does not apply to living objects, which are open systems and constantly decrease entropy, creating perfectly ordered molecules, for example, due to the energy of sunlight. Living systems are characterized by self-organization, which the Chilean neuroscientist Humberto Maturana called autopoiesis (self-creation) in 1970. Living systems not only constantly move away from classical thermodynamic equilibrium, but also make the environment unbalanced. Back in 1965, American atmospheric chemist James Lovelock proposed assessing the equilibrium composition of the atmosphere as a criterion for the presence of life on Mars. The Earth's atmosphere simultaneously contains oxygen (21% by volume), methane (0.00018%), hydrogen (0.00005%), carbon monoxide (0.00001%) - this is clearly a non-equilibrium mixture at temperatures C. The Earth's atmosphere is an open system, in the formation of which living organisms constantly participate. The atmosphere of Mars is dominated by carbon dioxide (95% - compare with 0.035% on Earth), oxygen is less than 1%, and reducing gases (methane) have not yet been discovered. Consequently, the atmosphere of Mars is practically in equilibrium; all reactions between the gases contained in it have already taken place. From these data, Lovelock concluded that there is currently no life on Mars. Gibbs Energy The introduction of entropy made it possible to establish criteria to determine the direction and depth of any chemical process (for a large number of particles in equilibrium). Macroscopic systems reach equilibrium when the change in energy is compensated by the entropy component: At constant pressure and temperature: ΔH p = TΔS p or Δ(H-TS) ΔG = 0 Gibbs energy[ 6 ] or Gibbs free energy or isobaric-isothermal potential Change in Gibbs energy as a criterion for the possibility of a chemical reaction For a given temperature ΔG = ΔH - TΔS At ΔG< 0 реакция возможна; при ΔG >0 reaction is not possible; at ΔG = 0 the system is in equilibrium. 6 Gibbs Josiah Willard (), American physicist and mathematician, one of the founders of chemical thermodynamics and statistical physics. Gibbs published a fundamental treatise on the equilibrium of heterogeneous substances (On the Equilibrium of Heterogeneous Substances), which became the basis of chemical thermodynamics. 15
6 The possibility of a spontaneous reaction in an isolated system is determined by a combination of the signs of the energy (enthalpy) and entropy factors: Sign ΔH Sign ΔS Possibility of a spontaneous reaction + No + Yes Depends on the ratio of ΔH and TΔS + + Depends on the ratio of ΔH and TΔS There are extensive tabular data on standard values ΔG 0 and S 0, allowing you to calculate ΔG 0 of the reaction. 5. Chemical kinetics Predictions of chemical thermodynamics are most correct in their prohibitive part. If, for example, for the reaction of nitrogen with oxygen the Gibbs energy is positive: N 2 + O 2 = 2 NO ΔG 0 = +176 kJ, then this reaction will not proceed spontaneously, and no catalyst will help it. The well-known factory process for obtaining NO from air requires enormous amounts of energy and a non-equilibrium process (hardening of products by rapid cooling after passing a mixture of gases through an electric arc). On the other hand, not all reactions for which ΔG< 0, спешат осуществиться на практике. Куски каменного угля могут веками лежать на воздухе, хотя для реакции C + O 2 = CO 2 ΔG 0 = -395 кдж Предсказание скорости химической реакции, а также выяснение зависимости этой скорости от условий проведения реакции осуществляет химическая кинетика наука о химическом процессе, его механизме и закономерностях протекания во времени. Скорость химической реакции определяется как изменение концентрации одного из участвующих в реакции веществ (исходное вещество или продукт реакции) в единицу времени. Для реакции в общем виде aa + bb xx + yy скорость описывается кинетическим уравнением: v = -ΔC (A) /Δt = ΔC (X) /Δt = k C m n (A) C (B) k называется константой скорости реакции. Строго говоря, скорость определяется не как конечная разность концентраций, а как их производная v = -dc (A) /dt; степенные показатели m и n обычно не совпадают со стехиометрическими коэффициентами в уравнении реакции. Порядком реакции называется сумма всех показателей степеней m и n. Порядок реакции по реагенту A равен m. Большинство реакций являются многостадийными, даже если они описываются простыми стехиометрическими уравнениями. В этом случае обычно получается сложное кинетическое уравнение реакции. Например, для реакции H 2 + Br 2 = 2 HBr dc (HBr) /dt = kc (H2) C (Br2) 0,5 / (1 + k C (HBr) / C (Br2)) 16
7 Such a complex dependence of the rate on concentrations indicates a multistage reaction mechanism. A chain mechanism has been proposed for this reaction: Br 2 Br. + Br. Br chain nucleation. + H 2 HBr + H. continuation of the chain H. + Br 2 HBr + Br. continuation of the chain H. + HBr H 2 + Br. Br inhibition. + Br. Br 2 chain termination The number of reagent molecules participating in a simple one-step reaction consisting of one elementary act is called the molecularity of the reaction. Monomolecular reaction: C 2 H 6 = 2 CH 3. Bimolecular reaction: CH 3. + CH 3. = C 2 H 6 Examples of relatively rare trimolecular reactions: 2 NO + O 2 = 2 NO 2 2 NO + Cl 2 = 2 NOCl H. + H. + Ar = H 2 + Ar A feature of 1st order reactions proceeding according to the scheme: A products is the constancy of the half-conversion time t 0.5, the time during which half of the original substance will turn into products. This time is inversely proportional to the reaction rate constant k. t 0.5 = 0.693/k i.e. The half-life of a first-order reaction is a constant and characteristic of the reaction. In nuclear physics, the half-life of a radioactive isotope is its important property. Dependence of reaction rates on temperature. Most practically important reactions are accelerated when heated. The dependence of the reaction rate constant on temperature is expressed by the Arrhenius equation [7] (1889): k = Aexp(-E a /RT) The factor A is related to the frequency of particle collisions and their orientation during collisions; E a is the activation energy of a given chemical reaction. To determine the activation energy of a given reaction, it is enough to measure its rate at two temperatures. The Arrhenius equation describes the temperature dependence not only for simple chemical processes. Psychological studies of people with different body temperatures (from 36.4 to 39 o C) showed that the subjective sense of time (clock counting speed) and 7 Svante August Arrhenius () Swedish physical chemist, creator of the theory electrolytic dissociation, academician of the Royal Swedish Academy of Sciences. Based on ideas about the formation of active particles in electrolyte solutions, Arrhenius put forward a general theory of the formation of “active” molecules during chemical reactions. In 1889, while studying the inversion of cane sugar, he showed that the rate of this reaction is determined by the collision of only “active” molecules. A sharp increase in this speed with increasing temperature is determined by a significant increase in the number of “active” molecules in the system. To enter into a reaction, molecules must have some additional energy compared to the average energy of the entire mass of molecules of a substance at a certain temperature (this additional energy will subsequently be called activation energy). Arrhenius outlined ways to study the nature and type of temperature dependence of reaction rate constants. 17
8, the rate of forgetting of random sequences of characters is described by the Arrhenius equation with an activation energy of 190 kJ/mol [8]. A positive value of activation energy shows that there is an energy barrier on the path from starting substances to products, which does not allow all thermodynamically possible reactions to occur immediately: Figure 2. Activation energy (at what point is it reported to the match?) 8. Leenson I.A. Why and how chemical reactions occur. M.: MIROS, s, s
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L15 Law of conservation of energy in open systems closed system internal energy U entropy S(U) k lnw (U) temperature ds 1 du Due to the lack of contact with the external environment, internal energy in this
“FUNDAMENTALS OF CHEMICAL THERMODYNAMICS, CHEMICAL KINETICS AND EQUILIBRIUM”
Fundamentals of chemical thermodynamics
1 . What does chemical thermodynamics study:
1) the rate of chemical transformations and the mechanisms of these transformations;
2) energy characteristics of physical and chemical processes and the ability of chemical systems to perform useful work;
3) conditions for shifting chemical equilibrium;
4) the influence of catalysts on the rate of biochemical processes.
2. An open system is a system that:
3. A closed system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
4. An isolated system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
5. To what type of thermodynamic systems does the solution located in a sealed ampoule placed in a thermostat belong?
1) isolated;
2) open;
3) closed;
4) stationary.
6. What type of thermodynamic systems does the solution in the sealed ampoule belong to?
1) isolated;
2) open;
3) closed;
4) stationary.
7. What type of thermodynamic systems does a living cell belong to?
1) open;
2) closed;
3) isolated;
4) equilibrium.
8 . What parameters of a thermodynamic system are called extensive?
1) the magnitude of which does not depend on the number of particles in the system;
3) the value of which depends on the state of aggregation of the system;
9. What parameters of a thermodynamic system are called intensive?
!) whose magnitude does not depend on the number of particles in the system;
2) the magnitude of which depends on the number of particles in the system;
3) the value of which depends on the state of aggregation;
4) the magnitude of which depends on time.
10 . Functions of the state of a thermodynamic system are quantities that:
1) depend only on the initial and final state of the system;
2) depend on the process path;
3) depend only on the initial state of the system;
4) depend only on the final state of the system.
11 . What quantities are functions of the state of the system: a) internal energy; b) work; c) warmth; d) enthalpy; d) entropy.
3) all quantities;
4) a, b, c, d.
12 . Which of the following properties are intensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
3) b, c, d, f;
13. Which of the following properties are extensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
3) b, c, d, f;
14 .
What forms of energy exchange between the system and the environment are considered by thermodynamics: a) heat; b) work; c) chemical; d) electric; e) mechanical; f) nuclear and solar?
2) c, d, e, f;
3) a, c, d, e, f;
15. Processes occurring at a constant temperature are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
16 .
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
17 Processes occurring at constant volume are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
18 . Processes occurring at constant pressure are called:
. The internal energy of a system is: 1) the entire energy reserve of the system, except for the potential energy of its position and the kinetic energy of the system as a whole;
2) the entire energy reserve of the system;
3) the entire energy reserve of the system, except for the potential energy of its position;
19 4) a quantity characterizing the degree of disorder in the arrangement of particles of the system.
. What law reflects the relationship between work, heat and internal energy of a system?
1) the second law of thermodynamics;
2) Hess's law;
3) the first law of thermodynamics;
20 4) van't Hoff's law.
. The first law of thermodynamics reflects the relationship between:
1) work, heat and internal energy;
2) Gibbs free energy, enthalpy and entropy of the system;
3) work and heat of the system;
21 4) work and internal energy.
.
22 Which equation is the mathematical expression of the first law of thermodynamics for isolated systems?
l)AU=0 2)AU=Q-p-AV 3)AG = AH-TAS
. Which equation is the mathematical expression of the first law of thermodynamics for closed systems?
23 1)AU=0; 2)AU=Q-p-AV;
3) AG = AH - T*AS;
.
24 Is the internal energy of an isolated system a constant or variable quantity?
1) constant;
2) variable.
. In an isolated system, the reaction of hydrogen combustion occurs with the formation of liquid water. Does the internal energy and enthalpy of the system change?
1) internal energy will not change, enthalpy will change;
25 2) internal energy will change, enthalpy will not change;
3) internal energy will not change, enthalpy will not change;
4) internal energy will change, enthalpy will change.
.
26 Under what conditions is the change in internal energy equal to the heat received by the system from the environment?
1) at constant volume;
3) at constant pressure;
4) under no circumstances.
. The thermal effect of a reaction occurring at constant volume is called a change:
27 1) enthalpy;
28. 2) internal energy;
3) entropy;
4) Gibbs free energy.
. The enthalpy of a reaction is:
Chemical processes during which the enthalpy of the system decreases and heat is released into the external environment are called:
29 1) endothermic;
3) internal energy will not change, enthalpy will not change;
2) at constant temperature;
4) internal energy will change, enthalpy will change.
.
30 . The thermal effect of a reaction occurring at constant pressure is called a change:
1) internal energy;
2) none of the previous definitions are correct;
3) enthalpy;
4) entropy.
31. What processes are called endothermic?
32 . What processes are called exothermic?
1) for which AN is negative;
2) for which AG is negative;
3) for which AN is positive;
4) for which AG is positive.
33 . Specify the formulation of Hess's law:
1) the thermal effect of the reaction depends only on the initial and final state of the system and does not depend on the reaction path;
2) the heat absorbed by the system at a constant volume is equal to the change in the internal energy of the system;
3) the heat absorbed by the system at constant pressure is equal to the change in enthalpy of the system;
4) the thermal effect of the reaction does not depend on the initial and final state of the system, but depends on the reaction path.
34. What law underlies the calculation of caloric content of food?
1) van't Hoff;
3) Sechenov;
35. When oxidizing which substances under body conditions, more energy is released?
1) proteins;
3) carbohydrates;
4) carbohydrates and proteins.
36 . A spontaneous process is a process that:
1) carried out without the help of a catalyst;
2) accompanied by the release of heat;
3) carried out without external energy consumption;
4) proceeds quickly.
37 . Entropy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
2) the amount of heat that is released or absorbed during a chemical reaction under isochoric-isothermal conditions;
3) a value characterizing the possibility of spontaneous occurrence of the process;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in the system.
38 . What state function characterizes the tendency of a system to achieve a probable state that corresponds to the maximum randomness of the distribution of particles?
1) enthalpy;
2) entropy;
3) Gibbs energy;
4) internal energy.
39 . What is the relationship between the entropies of three aggregate states of one substance: gas, liquid, solid:
I) S (g) > S (g) > S (tv); 2) S(solid)>S(g)>S(g); 3)S(g)>S(g)>S(TB); 4) the state of aggregation does not affect the entropy value.
40 . Which of the following processes should exhibit the greatest positive change in entropy:
1) CH3OH (s) --> CH,OH (g);
2) CH4OH (s) --> CH 3 OH (l);
3) CH,OH (g) -> CH4OH (s);
4) CH,OH (l) -> CH3OH (sol).
41 . Choose the correct statement: the entropy of the system increases when:
1) increased pressure;
2) transition from liquid to solid state of aggregation
3) increase in temperature;
4) transition from gaseous to liquid state.
42. What thermodynamic function can be used to predict whether a reaction will occur spontaneously in an isolated system?
1) enthalpy;
2) internal energy;
3) entropy;
4) potential energy of the system.
43 .
44 Which equation is the mathematical expression of the 2nd law of thermodynamics for isolated systems?
. If the system reversibly receives a quantity of heat Q at temperature T, then about T;
2) increases by the amount Q/T;
3) increases by an amount greater than Q/T;
45 4) increases by an amount less than Q/T.
.
In an isolated system, a chemical reaction occurs spontaneously to form a certain amount of product. How does the entropy of such a system change?
1) increases
2) decreases
46 3) does not change
4) reaches the minimum value
.
Indicate in which processes and under what conditions the change in entropy can be equal to the work of the process? 47 1) in isobaric conditions, at constant P and T;
2) in isochoric conditions, at constant V and T;
H) the change in entropy is never equal to work; 4) in isothermal conditions, at constant P and
. How will the bound energy of the system TS change when heated and when it condenses?
1) increases with heating, decreases with condensation;
48 2) decreases with heating, increases with condensation;
3) there is no change in T-S;
4) increases with heating and condensation.
. What parameters of the system must be kept constant so that the sign of the change in entropy can be used to judge the direction of the spontaneous course of the process?
1) pressure and temperature;
49 2) volume and temperature;
3) internal energy and volume;
4) only temperature.
. In an isolated system, all spontaneous processes proceed in the direction of increasing disorder. How does entropy change?
1) does not change;
50 2) increases;
3) decreases;
4) first increases and then decreases.
. Entropy increases by the amount Q/T for:
1) reversible process;
51 2) an irreversible process;
3) homogeneous;
4) heterogeneous.
52 How does the entropy of the system change due to forward and reverse reactions during ammonia synthesis?
3) entropy does not change during the reaction;
2) enthalpy and entropy;
3) entropy and temperature;
4) changes in Gibbs energy and temperature.
53. Under isobaric-isothermal conditions, the maximum work performed by the system is:
1) equal to the decrease in Gibbs energy;
2) greater loss of Gibbs energy;
3) less loss of Gibbs energy;
4) is equal to the loss of enthalpy.
54 .
What conditions must be met so that the maximum work in the system is accomplished due to the decrease in Gibbs energy?
1) it is necessary to maintain constant V and t;
2) it is necessary to maintain constant P and t;
3) it is necessary to maintain constant AH and AS;
55 4) it is necessary to maintain constant P&V
.
What causes the maximum useful work done in a chemical reaction at constant pressure and temperature?
1) due to the decrease in Gibbs energy;
56. 3) due to an increase in enthalpy;
4) due to a decrease in entropy.
Due to what is the maximum useful work done by a living organism under isobaric-isothermal conditions?
1) due to the loss of enthalpy;
2) due to an increase in entropy;
57 3) due to the decrease in Gibbs energy;
58. 4) due to an increase in the Gibbs energy.
. What processes are called endergonic?
59. What processes are called exergonic?
2) AG 0; 4) AG > 0.
3) enthalpy;
The spontaneous nature of the process is best determined by assessing:
1) entropy;
60 2) Gibbs free energy;
1) enthalpy;
3) entropy;
2) internal energy;
4) temperature.
61 . What thermodynamic function can be used to predict the possibility of spontaneous processes occurring in a living organism?
4) Gibbs free energy.
.
For reversible processes, the change in Gibbs free energy...
62 1) always equal to zero;
4) Gibbs free energy.
.
For reversible processes, the change in Gibbs free energy...
2) always negative;
63. 3) always positive;
.
4) only temperature.
. In an isolated system, all spontaneous processes proceed in the direction of increasing disorder. How does entropy change?
For irreversible processes, the change in free energy:
64 4) positive or negative depending on the circumstances.
Under isobaric-isothermal conditions, only such processes can spontaneously occur in a system, as a result of which the Gibbs energy is:
1) does not change;
4) reaches its maximum value.
. For a certain chemical reaction in the gas phase at constant P and TAG > 0. In what direction does this reaction spontaneously proceed?
65 D) in the forward direction;
66 2) cannot occur under these conditions;
3) in the opposite direction;
4) is in a state of equilibrium.
67. . What is the sign AG of the ice melting process at 263 K?
. In which of the following cases is the reaction not feasible at any temperature?
68 1)AH>0;AS>0; 2)AH>0;AH
3)A#4)AH= 0;AS = 0.
2) for any ratio of AN and TAS; 3)(AH]
4) [AN] = [T-A S].
69 . At what values of the sign of AH and AS are only exothermic processes possible in the system?
70. At what ratios of AN and T* AS is the chemical process directed towards an endothermic reaction:
71 . At what constant thermodynamic parameters can a change in enthalpy serve as a criterion for the direction of a spontaneous process? What sign of DH under these conditions indicates a spontaneous process?
1) at constant S and P, AN
3) with constant Put, AN
2) at constant 5 and P, AN > 0; 4) at constant Vn t, AH > 0.
72 . Is it possible and in what cases to judge by the sign of the change in enthalpy during a chemical reaction about the possibility of its occurrence at constant Ti P1
1) possible, if LA » T-AS;
2) under these conditions it is impossible;
3) possible, if AN « T-AS;
4) possible if AN = T-AS.
73 . The reaction ZN 2 + N 2 -> 2NH 3 is carried out at 110°C, so that all reactants and products are in the gas phase. Which of the following values is conserved during the reaction?
2) entropy;
3) enthalpy;
74 .
Which of the following statements are true for reactions occurring under standard conditions?
1) endothermic reactions cannot occur spontaneously;
2) endothermic reactions can occur at sufficiently low temperatures;
3) endothermic reactions can occur at high temperatures if AS > 0;
75 4) endothermic reactions can occur at high temperatures if AS
. What are the features of biochemical processes: a) obey the principle of energy coupling; b) usually reversible; c) complex; d) only exergonic (AG
1) a, b, c, d;
76 2) b, c, d; 3) a, 6, c; 4) c, d.
77 . Exergonic reactions in the body occur spontaneously, since:
78 . Endergonic reactions in the body require energy supply, since: 1) AG >0;
. When any peptide AH 0 is hydrolyzed, will this process occur spontaneously?
1) will be, since AG > 0;
3) will not happen, since AG > 0;
2) will be, since AG
79 4) will not be, since AG
. The calorie content of nutrients is called energy:
1) 1 g of nutrients released during complete oxidation;
2) 1 mole of nutrients released during complete oxidation;
3) necessary for complete oxidation of 1 g of nutrients;
80 4) 1 mole of nutrients required for complete oxidation.
. For the process of thermal denaturation of many enzymes, LA > 0 and AS > 0. Can this process occur spontaneously?
2) can at low temperatures, since \T-AS\
3) cannot, since \T-AS\ > |AH];
4) cannot, because \T-AS\
81 . For the process of thermal hydration of many AN proteins
1) can at sufficiently low temperatures, since |AH| > \T-AS\;
2) can at sufficiently low temperatures, since |АА|
3) can at high temperatures, since |AH)
4) cannot at any temperature.
ProgramParameters chemical reactions, chemical equilibrium; - calculate thermal effects and speed chemical reactions... reactions; - basics physical and colloid chemistry, chemical kinetics, electrochemistry, chemical thermodynamics and thermochemistry; ...
Objectives of the graduate’s professional activity. Graduate competencies formed as a result of mastering a higher education program. Documents regulating the content and organization of the educational process during the implementation of higher educational education (3)
RegulationsModule 2. Basic physics chemical patterns of occurrence chemical processes Basics chemical thermodynamics. Basics chemical kinetics. Chemical equilibrium. Module 3.. Basics chemistry of solutions General...
This manual can be used for independent work by students of non-chemical specialties
DocumentSimple substances. In this basis V chemical thermodynamics a system for calculating thermal effects has been created..., Cr2O3? TOPIC 2. CHEMICAL KINETICS AND CHEMICAL EQUILIBRIUM As was shown earlier, chemical thermodynamics allows you to predict the fundamental...
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Working programm4.1.5. Redox processes. Basics electrochemistry Oxidation-reduction processes. ... Methods for quantitatively expressing the composition of solutions. 5 Chemical thermodynamics 6 Kinetics And equilibrium. 7 Dissociation, pH, hydrolysis 8 ...
1 . What does chemical thermodynamics study:
1) the rate of chemical transformations and the mechanisms of these transformations;
2) energy characteristics of physical and chemical processes and the ability of chemical systems to perform useful work;
3) conditions for shifting chemical equilibrium;
4) the influence of catalysts on the rate of biochemical processes.
2. An open system is a system that:
2) exchanges both matter and energy with the environment;
3. A closed system is a system that:
1) does not exchange either matter or energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
4. An isolated system is a system that:
1) does not exchange either matter or energy with the environment;
2) exchanges both matter and energy with the environment;
3) exchanges energy with the environment, but does not exchange matter;
4) exchanges matter with the environment, but does not exchange energy.
5. To what type of thermodynamic systems does the solution located in a sealed ampoule placed in a thermostat belong?
1) isolated;
2) open;
3) closed;
4) stationary.
6. What type of thermodynamic systems does the solution in the sealed ampoule belong to?
1) isolated;
2) open;
3) closed;
4) stationary.
7. What type of thermodynamic systems does a living cell belong to?
1) open;
2) closed;
3) isolated;
4) equilibrium.
8 . What parameters of a thermodynamic system are called extensive?
1) the magnitude of which does not depend on the number of particles in the system;
2) whose value depends on the number of particles in the system;
3) the value of which depends on the state of aggregation of the system;
9. What parameters of a thermodynamic system are called intensive?
!) the magnitude of which does not depend on the number of particles in the system;
2) the magnitude of which depends on the number of particles in the system;
3) the value of which depends on the state of aggregation;
4) the magnitude of which depends on time.
10 . Functions of the state of a thermodynamic system are quantities that:
1) depend only on the initial and final state of the system;
2) depend on the process path;
3) depend only on the initial state of the system;
4) depend only on the final state of the system.
11 . What quantities are functions of the state of the system: a) internal energy; b) work; c) warmth; d) enthalpy; d) entropy.
1) a, d, e;
3) all quantities;
4) a, b, c, d.
12 . Which of the following properties are intensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
1) a, b, d;
3) b, c, d, f;
13. Which of the following properties are extensive: a) density; b) pressure; c) mass; d) temperature; e) enthalpy; e) volume?
1) c, d, f;
3) b, c, d, f;
14 . What forms of energy exchange between the system and the environment are considered by thermodynamics: a) heat; b) work; c) chemical; d) electric; e) mechanical; f) nuclear and solar?
1)a, b;
2) c, d, e, f;
3) a, c, d, e, f;
4) a, c, d, e.
15. Processes occurring at a constant temperature are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
16 . Processes occurring at constant volume are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
17 . Processes occurring at constant pressure are called:
1) isobaric;
2) isothermal;
3) isochoric;
4) adiabatic.
18 . The internal energy of the system is: 1) the entire energy reserve of the system, except for the potential energy of its position andkinetic energysystems as a whole;
2) the entire energy reserve of the system;
3) the entire energy reserve of the system, except for the potential energy of its position;
4) a quantity characterizing the degree of disorder in the arrangement of particles of the system.
19 . What law reflects the relationship between work, heat and internal energy of a system?
1) second law of thermodynamics;
2) Hess's law;
3) the first law of thermodynamics;
4) van't Hoff's law.
20 . The first law of thermodynamics reflects the relationship between:
1) work, heat and internal energy;
2) Gibbs free energy, enthalpy and entropy of the system;
3) work and heat of the system;
4) work and internal energy.
21 . Which equation is the mathematical expression of the first law of thermodynamics for isolated systems?
l)AU=0 2)AU=Q-p-AV 3)AG = AH-TAS
22 . Which equation is the mathematical expression of the first law of thermodynamics for closed systems?
2)AU=Q-p-AV;
. Which equation is the mathematical expression of the first law of thermodynamics for closed systems?
23 . Is the internal energy of an isolated system a constant or variable quantity?
1) constant;
2) variable.
24 . In an isolated system, the reaction of hydrogen combustion occurs with the formation of liquid water. Does the internal energy and enthalpy of the system change?
1) internal energy will not change, enthalpy will change;
2) internal energy will change, enthalpy will not change;
3) internal energy will not change, enthalpy will not change;
4) internal energy will change, enthalpy will change.
25 . Under what conditions is the change in internal energy equal to the heat received by the system from the environment?
1) at constant volume;
3) at constant pressure;
4) under no circumstances.
26 . The thermal effect of a reaction occurring at constant volume is called a change:
1) enthalpy;
2) internal energy;
3) entropy;
4) Gibbs free energy.
27 . The enthalpy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in the system.
28. 2) internal energy;
1) endothermic;
2) exothermic;
3) exergonic;
4) endergonic.
29 . Under what conditions is the change in enthalpy equal to the heat received by the system from the environment?
1) at constant volume;
2) at constant temperature;
3) at constant pressure;
4) under no circumstances.
30 . The thermal effect of a reaction occurring at constant pressure is called a change:
1) internal energy;
2) none of the previous definitions are correct;
3) enthalpy;
4) entropy.
31. What processes are called endothermic?
1) for which AN is negative;
3) for whichANpositively;
32 . What processes are called exothermic?
1) for whichANnegative;
2) for which AG is negative;
3) for which AN is positive;
4) for which AG is positive.
33 . Specify the formulation of Hess's law:
1) the thermal effect of the reaction depends only on the initial and final state of the system and does not depend on the reaction path;
2) the heat absorbed by the system at a constant volume is equal to the change in the internal energy of the system;
3) the heat absorbed by the system at constant pressure is equal to the change in enthalpy of the system;
4) the thermal effect of the reaction does not depend on the initial and final state of the system, but depends on the reaction path.
34. What law underlies the calculation of caloric content of food?
1) van't Hoff;
2) Hess;
3) Sechenov;
35. When oxidizing which substances under body conditions, more energy is released?
1) proteins;
2) fat;
3) carbohydrates;
4) carbohydrates and proteins.
36 . A spontaneous process is a process that:
1) carried out without the help of a catalyst;
2) accompanied by the release of heat;
3) carried out without external energy consumption;
4) proceeds quickly.
37 . Entropy of a reaction is:
1) the amount of heat that is released or absorbed during a chemical reaction under isobaric-isothermal conditions;
2) the amount of heat that is released or absorbed during a chemical reaction under isochoric-isothermal conditions;
3) a value characterizing the possibility of spontaneous occurrence of the process;
4) a quantity characterizing the degree of disorder in the arrangement and movement of particles in a system.
38 . What state function characterizes the tendency of a system to achieve a probable state that corresponds to the maximum randomness of the distribution of particles?
1) enthalpy;
2) entropy;
3) Gibbs energy;
4) internal energy.
39 . What is the relationship between the entropies of three aggregate states of one substance: gas, liquid, solid:
I) S(d) >S(g) >S(TV); 2) S(solid)>S(g)>S(g); 3)S(g)>S(g)>S(TB); 4) the state of aggregation does not affect the entropy value.
40 . Which of the following processes should exhibit the greatest positive change in entropy:
1) CH3OH (s) --> CH,OH (g);
2) CH3OH (s) --> CH 3 OH (l);
3) CH,OH (g) -> CH3OH (s);
4) CH,OH (l) -> CH3OH (sol).
41 . Choose the correct statement: the entropy of the system increases when:
1) increased pressure;
2) transition from liquid to solid state of aggregation
3) temperature increase;
4) transition from gaseous to liquid state.
42. What thermodynamic function can be used to predict whether a reaction will occur spontaneously in an isolated system?
1) enthalpy;
2) internal energy;
3) entropy;
4) potential energy of the system.
43 . Which equation is the mathematical expression of the 2nd law of thermodynamics for isolated systems?
2)AS>Q\T
44 . If the system reversibly receives an amount of heat Q at temperature T, then about T;
2) increases by the amountQ/ T;
3) increases by an amount greater than Q/T;
4) increases by an amount less than Q/T.
45 . In an isolated system, a chemical reaction occurs spontaneously to form a certain amount of product. How does the entropy of such a system change?
1) increases
2) decreases
3) does not change
4) reaches the minimum value
46 . Indicate in which processes and under what conditions the change in entropy can be equal to the work of the process?
1) in isobaric conditions, at constant P and T;
2) in isochoric, at constant Vi and T;
H) the change in entropy is never equal to work;
4) in isothermal conditions, at constant P and 47 . How will the bound energy of the system TS change when heated and when it condenses?
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