Main article: Le Chatelier-Brown principle
The position of chemical equilibrium depends on the following reaction parameters: temperature, pressure and concentration. The influence that these factors have on chemical reaction, obey the pattern that was expressed in general view in 1885 by the French scientist Le Chatelier.
Factors influencing chemical equilibrium:
1) temperature
As the temperature increases, the chemical equilibrium shifts towards the endothermic (absorption) reaction, and when it decreases, towards the exothermic (release) reaction.
CaCO 3 =CaO+CO 2 -Q t →, t↓ ←
N 2 +3H 2 ↔2NH 3 +Q t ←, t↓ →
2) pressure
As pressure increases, the chemical equilibrium shifts towards a smaller volume of substances, and as pressure decreases towards a larger volume. This principle only applies to gases, i.e. If solids are involved in the reaction, they are not taken into account.
CaCO 3 =CaO+CO 2 P ←, P↓ →
1mol=1mol+1mol
3) concentration starting materials and reaction products
With an increase in the concentration of one of the starting substances, the chemical equilibrium shifts towards the reaction products, and with an increase in the concentration of the reaction products, towards the starting substances.
S 2 +2O 2 =2SO 2 [S],[O] →, ←
Catalysts do not affect the shift of chemical equilibrium!
Basic quantitative characteristics of chemical equilibrium: chemical equilibrium constant, degree of conversion, degree of dissociation, equilibrium yield. Explain the meaning of these quantities using the example of specific chemical reactions.
In chemical thermodynamics, the law of mass action relates the equilibrium activities of the starting substances and reaction products, according to the relationship:
Activity of substances. Instead of activity, concentration (for a reaction in an ideal solution), partial pressures (a reaction in a mixture of ideal gases), fugacity (a reaction in a mixture of real gases) can be used;
Stoichiometric coefficient (negative for starting substances, positive for products);
Chemical equilibrium constant. The subscript "a" here means the use of the activity value in the formula.
The efficiency of a reaction is usually assessed by calculating the yield of the reaction product (section 5.11). At the same time, the efficiency of the reaction can also be assessed by determining what part of the most important (usually the most expensive) substance was converted into the target reaction product, for example, what part of SO 2 was converted into SO 3 during the production of sulfuric acid, that is, find degree of conversion original substance.
Let a brief diagram of the ongoing reaction
Then the degree of conversion of substance A into substance B (A) is determined by the following equation
Where n proreact (A) – the amount of substance of reagent A that reacted to form product B, and n initial (A) – initial amount of reagent A. 
Naturally, the degree of transformation can be expressed not only through the amount of a substance, but also through any quantities proportional to it: the number of molecules (formula units), mass, volume.
If reagent A is taken in short supply and the loss of product B can be neglected, then the degree of conversion of reagent A is usually equal to the yield of product B
The exception is reactions in which the starting substance is obviously consumed to form several products. So, for example, in the reaction
Cl 2 + 2KOH = KCl + KClO + H 2 O
chlorine (reagent) is converted equally into potassium chloride and potassium hypochlorite. In this reaction, even with a 100% yield of KClO, the degree of conversion of chlorine into it is 50%.
The quantity you know - the degree of protolysis (section 12.4) - is a special case of the degree of conversion:
Within the framework of TED, similar quantities are called degree of dissociation acids or bases (also designated as the degree of protolysis). The degree of dissociation is related to the dissociation constant according to Ostwald's dilution law.
Within the framework of the same theory, the hydrolysis equilibrium is characterized by degree of hydrolysis (h), and the following expressions are used that relate it to the initial concentration of the substance ( With) and dissociation constants of weak acids (K HA) and weak bases formed during hydrolysis ( K MOH):
The first expression is valid for the hydrolysis of a salt of a weak acid, the second - salts of a weak base, and the third - salts of a weak acid and a weak base. All these expressions can only be used for dilute solutions with a degree of hydrolysis of no more than 0.05 (5%).
Typically, the equilibrium yield is determined by a known equilibrium constant, with which it is related in each specific case by a certain ratio.
The yield of the product can be changed by shifting the equilibrium of the reaction in reversible processes, influenced by factors such as temperature, pressure, concentration.
In accordance with Le Chatelier's principle, the equilibrium degree of conversion increases with increasing pressure during simple reactions, and in other cases the volume of the reaction mixture does not change and the yield of the product does not depend on pressure.
The effect of temperature on the equilibrium yield, as well as on the equilibrium constant, is determined by the sign of the thermal effect of the reaction.
For a more complete assessment of reversible processes, the so-called yield from the theoretical (yield from the equilibrium) is used, equal to the ratio of the actually obtained product to the amount that would be obtained in a state of equilibrium.
THERMAL DISSOCIATION chemical
a reaction of reversible decomposition of a substance caused by an increase in temperature.
With Etc., several (2H2H+ OCaO + CO) or one simpler substance are formed from one substance
Equilibrium etc. is established according to the law of mass action. It
can be characterized either by an equilibrium constant or by the degree of dissociation
(the ratio of the number of decayed molecules to the total number of molecules). IN
In most cases, etc. is accompanied by the absorption of heat (increase
enthalpy
DN>0); therefore, in accordance with Le Chatelier-Brown principle
heating enhances it, the degree of displacement etc. with temperature is determined
absolute value of DN. The pressure interferes with etc., the more strongly, the greater
change (increase) in the number of moles (Di) of gaseous substances
the degree of dissociation does not depend on pressure. If solids are not
form solid solutions and are not in a highly dispersed state,
then the pressure etc. is uniquely determined by the temperature. To implement T.
d. solids (oxides, crystalline hydrates, etc.)
important to know
temperature at which the dissociation pressure becomes equal to the external one (in particular,
atmospheric) pressure. Since the gas released can overcome
ambient pressure, then upon reaching this temperature the decomposition process
immediately intensifies.
Dependence of the degree of dissociation on temperature: the degree of dissociation increases with increasing temperature (increasing temperature leads to an increase in the kinetic energy of dissolved particles, which promotes the disintegration of molecules into ions) 
The degree of conversion of starting substances and the equilibrium yield of the product. Methods for their calculation at a given temperature. What data is needed for this? Give a scheme for calculating any of these quantitative characteristics of chemical equilibrium using an arbitrary example.
The degree of conversion is the amount of reacted reagent divided by its original amount. For the simplest reaction, where is the concentration at the inlet to the reactor or at the beginning of the periodic process, is the concentration at the outlet of the reactor or the current moment of the periodic process. For a voluntary response, for example, 
, in accordance with the definition, the calculation formula is the same: . If there are several reagents in a reaction, then the degree of conversion can be calculated for each of them, for example, for the reaction 
The dependence of the degree of conversion on the reaction time is determined by the change in the concentration of the reagent over time. At the initial moment of time, when nothing has transformed, the degree of transformation is zero. Then, as the reagent is converted, the degree of conversion increases. For an irreversible reaction, when nothing prevents the reagent from being completely consumed, its value tends (Fig. 1) to unity (100%). 
Fig. 1 The greater the rate of reagent consumption, determined by the value of the rate constant, the faster the degree of conversion increases, as shown in the figure. If the reaction is reversible, then as the reaction tends to equilibrium, the degree of conversion tends to the equilibrium value, the value of which depends on the ratio of the rate constants of the forward and reverse reactions (on the equilibrium constant) (Fig. 2). 
Fig. 2 Yield of the target product Yield of the product is the amount of the target product actually obtained, divided by the amount of this product that would have been obtained if all the reagent had passed into this product (to the maximum possible amount of the resulting product). Or (through the reagent): the amount of the reagent actually converted into the target product, divided by the initial amount of the reagent. For the simplest reaction, the yield is , and keeping in mind that for this reaction, 
, i.e. For the simplest reaction, the yield and the degree of conversion are the same value. If the transformation takes place with a change in the amount of substances, for example, then, in accordance with the definition, the stoichiometric coefficient must be included in the calculated expression. In accordance with the first definition, the imaginary amount of product obtained from the entire initial amount of the reagent will be for this reaction two times less than the original amount of the reagent, i.e. , and the calculation formula. In accordance with the second definition, the amount of the reagent actually converted into the target product will be twice as large as this product was formed, i.e. , then the calculation formula is . Naturally, both expressions are the same. For a more complex reaction, the calculation formulas are written in exactly the same way in accordance with the definition, but in this case the yield is no longer equal to the degree of conversion. For example, for the reaction, 
. If there are several reagents in a reaction, the yield can be calculated for each of them; if there are also several target products, then the yield can be calculated for any target product for any reagent. As can be seen from the structure of the calculation formula (the denominator contains a constant value), the dependence of the yield on the reaction time is determined by the time dependence of the concentration of the target product. So, for example, for the reaction 
this dependence looks like in Fig. 3. 
Fig.3
The degree of conversion as a quantitative characteristic of chemical equilibrium. How will an increase in total pressure and temperature affect the degree of conversion of the reagent ... in a gas-phase reaction: ( the equation is given)? Provide a rationale for your answer and appropriate mathematical expressions.
The transition of a chemical system from one equilibrium state to another is called displacement (shift) of equilibrium. Due to the dynamic nature of chemical equilibrium, it is sensitive to external conditions and is able to respond to their changes.
The direction of the shift in the position of chemical equilibrium as a result of changes in external conditions is determined by the rule first formulated by the French chemist and metallurgist Henri Louis Le Chatelier in 1884 and named after him Le Chatelier's principle:
If an external influence is exerted on a system in a state of equilibrium, then a shift in equilibrium occurs in the system that weakens this influence.
There are three main parameters, changing which you can shift the chemical equilibrium. These are temperature, pressure and concentration. Let us consider their influence using the example of an equilibrium reaction:
1) Effect of temperature. Since for this reaction DH°<0, следовательно, прямая реакция идет с выделением тепла (+Q), а обратная реакция – с поглощением тепла (-Q):
2NO (G) + O 2 (G) 2NO 2 (G)
When the temperature rises, i.e. When additional energy is introduced into the system, the equilibrium shifts towards the reverse endothermic reaction, which consumes this excess energy. When the temperature decreases, on the contrary, the equilibrium shifts towards the reaction that occurs with the release of heat so that it compensates for the cooling, i.e. the equilibrium shifts towards the direct reaction.
As the temperature rises, the equilibrium shifts towards an endothermic reaction, which involves the absorption of energy.
As the temperature decreases, the equilibrium shifts towards an exothermic reaction that releases energy.
2) Effect of volume. As the pressure increases, the rate of the reaction that occurs with a decrease in volume increases to a greater extent (DV<0). При понижении давления ускоряется реакция, протекающая с увеличением объема (DV>0).
When the reaction under consideration occurs, 2 moles of gases are formed from 3 moles of gaseous substances:
2NO (G) + O 2 (G) 2NO 2 (G)
3 moles of gas 2 moles of gas
V OUT > V PROD
DV = V PROD - V OUT<0
Therefore, as the pressure increases, the equilibrium shifts towards a smaller volume of the system, i.e. reaction products. As the pressure decreases, the equilibrium shifts towards the starting substances, which occupy a larger volume
As pressure increases, the equilibrium shifts toward the reaction that produces fewer moles of gaseous substances.
As the pressure decreases, the equilibrium shifts toward the reaction that produces more moles of gaseous substances.
3) Effect of concentration. As the concentration increases, the rate of reaction by which the injected substance is consumed increases. Indeed, when additional oxygen is introduced into the system, the system “consumes” it for a direct reaction to occur. When the concentration of O 2 decreases, this deficiency is compensated by the decomposition of the reaction product (NO 2) into the starting substances.
When the concentration of starting substances increases or the concentration of products decreases, the equilibrium shifts towards the direct reaction.
When the concentration of starting substances decreases or the concentration of products increases, the equilibrium shifts towards the reverse reaction.
The introduction of a catalyst into the system does not affect the shift in the position of chemical equilibrium, since the catalyst equally increases the rate of both forward and reverse reactions.
Chemical equilibrium is inherent reversible reactions and is not typical for irreversible chemical reactions.
Often, when carrying out a chemical process, the initial reactants are completely converted into reaction products. For example:
Cu + 4HNO 3 = Cu(NO 3) 2 + 2NO 2 + 2H 2 O
It is impossible to obtain metallic copper by carrying out the reaction in the opposite direction, because given the reaction is irreversible. In such processes, reactants are completely converted into products, i.e. the reaction proceeds to completion.
But the bulk of chemical reactions reversible, i.e. the reaction is likely to occur in parallel in the forward and reverse directions. In other words, the reactants are only partially converted into products and the reaction system will consist of both reactants and products. The system in this case is in the state chemical equilibrium.
In reversible processes, initially the direct reaction has a maximum speed, which gradually decreases due to a decrease in the amount of reagents. The reverse reaction, on the contrary, initially has a minimum speed, which increases as products accumulate. Eventually, a moment comes when the rates of both reactions become equal - the system reaches a state of equilibrium. When a state of equilibrium occurs, the concentrations of the components remain unchanged, but the chemical reaction does not stop. That. – this is a dynamic (moving) state. For clarity, here is the following figure:
Let's say there is a certain reversible chemical reaction:
a A + b B = c C + d D
then, based on the law of mass action, we write down expressions for directυ 1 and reverseυ 2 reactions:
v1 = k 1 ·[A] a ·[B] b
υ2 = k 2 ·[C] c ·[D] d
Able to chemical equilibrium, the rates of forward and reverse reactions are equal, i.e.:
k 1 ·[A] a ·[B] b = k 2 ·[C] c ·[D] d
we get
TO= k 1 / k 2 = [C] c [D] d ̸ [A] a [B] b
Where K =k 1 / k 2 – equilibrium constant.
For any reversible process, under given conditions k is a constant value. It does not depend on the concentrations of substances, because When the amount of one of the substances changes, the amounts of other components also change.
When the conditions of a chemical process change, the equilibrium may shift.
Factors influencing the shift in equilibrium:
- changes in concentrations of reagents or products,
- pressure change,
- temperature change,
- adding a catalyst to the reaction medium.
Le Chatelier's principle
All of the above factors influence the shift in chemical equilibrium, which obeys Le Chatelier's principle: If you change one of the conditions under which the system is in a state of equilibrium - concentration, pressure or temperature - then the equilibrium will shift in the direction of the reaction that counteracts this change. Those. equilibrium tends to shift in a direction leading to a decrease in the influence of the influence that led to a violation of the state of equilibrium.
So, let us consider separately the influence of each of their factors on the state of equilibrium.
Influence changes in concentrations of reactants or products let's show with an example Haber process:
N 2(g) + 3H 2(g) = 2NH 3(g)
If, for example, nitrogen is added to an equilibrium system consisting of N 2 (g), H 2 (g) and NH 3 (g), then the equilibrium should shift in a direction that would contribute to a decrease in the amount of hydrogen towards its original value, those. in the direction of the formation of additional ammonia (to the right). At the same time, the amount of hydrogen will decrease. When hydrogen is added to the system, the equilibrium will also shift towards the formation of a new amount of ammonia (to the right). Whereas the introduction of ammonia into the equilibrium system, according to Le Chatelier's principle , will cause a shift in equilibrium towards the process that is favorable for the formation of starting substances (to the left), i.e. The ammonia concentration should decrease through the decomposition of some of it into nitrogen and hydrogen.
A decrease in the concentration of one of the components will shift the equilibrium state of the system towards the formation of this component.
Influence pressure changes makes sense if gaseous components take part in the process under study and there is a change in the total number of molecules. If the total number of molecules in the system remains permanent, then the change in pressure no effect on its balance, for example:
I 2(g) + H 2(g) = 2HI (g)
If the total pressure of an equilibrium system is increased by decreasing its volume, then the equilibrium will shift towards decreasing volume. Those. towards decreasing the number gas in the system. In reaction:
N 2(g) + 3H 2(g) = 2NH 3(g)
from 4 gas molecules (1 N 2 (g) and 3 H 2 (g)) 2 gas molecules are formed (2 NH 3 (g)), i.e. the pressure in the system decreases. As a result, an increase in pressure will contribute to the formation of an additional amount of ammonia, i.e. the equilibrium will shift towards its formation (to the right).
If the temperature of the system is constant, then a change in the total pressure of the system will not lead to a change in the equilibrium constant TO.
Temperature change system affects not only the displacement of its equilibrium, but also the equilibrium constant TO. If additional heat is imparted to an equilibrium system at constant pressure, then the equilibrium will shift towards the absorption of heat. Consider:
N 2(g) + 3H 2(g) = 2NH 3(g) + 22 kcal
So, as you can see, the direct reaction proceeds with the release of heat, and the reverse reaction with absorption. As the temperature increases, the equilibrium of this reaction shifts towards the decomposition reaction of ammonia (to the left), because it appears and weakens the external influence - an increase in temperature. On the contrary, cooling leads to a shift in equilibrium in the direction of ammonia synthesis (to the right), because the reaction is exothermic and resists cooling.
Thus, an increase in temperature favors a shift chemical equilibrium towards the endothermic reaction, and the temperature drop towards the exothermic process . Equilibrium constants all exothermic processes decrease with increasing temperature, and endothermic processes increase.
The equilibrium state for a reversible reaction can last indefinitely (without outside intervention). But if an external influence is exerted on such a system (change the temperature, pressure or concentration of final or initial substances), then the state of equilibrium will be disrupted. The speed of one of the reactions will become greater than the speed of the other. Over time, the system will again occupy an equilibrium state, but the new equilibrium concentrations of the initial and final substances will differ from the original ones. In this case, they talk about a shift in chemical equilibrium in one direction or another.
If, as a result of an external influence, the rate of the forward reaction becomes greater than the rate of the reverse reaction, this means that the chemical equilibrium has shifted to the right. If, on the contrary, the rate of the reverse reaction becomes greater, this means that the chemical equilibrium has shifted to the left.
When the equilibrium shifts to the right, the equilibrium concentrations of the starting substances decrease and the equilibrium concentrations of the final substances increase compared to the initial equilibrium concentrations. Accordingly, the yield of reaction products also increases.
A shift of chemical equilibrium to the left causes an increase in the equilibrium concentrations of the starting substances and a decrease in the equilibrium concentrations of the final products, the yield of which will decrease.
The direction of the shift in chemical equilibrium is determined using Le Chatelier’s principle: “If an external influence is exerted on a system in a state of chemical equilibrium (change temperature, pressure, concentration of one or more substances participating in the reaction), this will lead to an increase in the rate of that reaction, the occurrence of which will compensate (reduce) the impact."
For example, as the concentration of starting substances increases, the rate of the forward reaction increases and the equilibrium shifts to the right. When the concentration of the starting substances decreases, on the contrary, the rate of the reverse reaction increases, and the chemical equilibrium shifts to the left.
When the temperature increases (i.e. when the system is heated), the equilibrium shifts towards the endothermic reaction, and when it decreases (i.e. when the system cools) - towards the exothermic reaction. (If the forward reaction is exothermic, then the reverse reaction will necessarily be endothermic, and vice versa).
It should be emphasized that an increase in temperature, as a rule, increases the rate of both forward and reverse reactions, but the rate of an endothermic reaction increases to a greater extent than the rate of an exothermic reaction. Accordingly, when the system is cooled, the rates of forward and reverse reactions decrease, but also not to the same extent: for an exothermic reaction it is significantly less than for an endothermic one.
A change in pressure affects the shift in chemical equilibrium only if two conditions are met:
it is necessary that at least one of the substances participating in the reaction be in a gaseous state, for example:
CaCO 3 (s) CaO (s) + CO 2 (g) - a change in pressure affects the displacement of the equilibrium.
CH 3 COOH (liquid) + C 2 H 5 OH (liquid) CH 3 COOC 2 H 5 (liquid) + H 2 O (liquid) – a change in pressure does not affect the shift in chemical equilibrium, because none of the starting or final substances is in a gaseous state;
if several substances are in the gaseous state, it is necessary that the number of gas molecules on the left side of the equation for such a reaction is not equal to the number of gas molecules on the right side of the equation, for example:
2SO 2 (g) + O 2 (g) 2SO 3 (g) – pressure changes affect the equilibrium shift
I 2(g) + H 2(g) 2НI (g) – pressure change does not affect the equilibrium shift
When these two conditions are met, an increase in pressure leads to a shift in equilibrium towards a reaction, the occurrence of which reduces the number of gas molecules in the system. In our example (catalytic combustion of SO 2) this will be a direct reaction.
A decrease in pressure, on the contrary, shifts the equilibrium towards the reaction that occurs with the formation of a larger number of gas molecules. In our example, this will be the opposite reaction.
An increase in pressure causes a decrease in the volume of the system, and therefore an increase in the molar concentrations of gaseous substances. As a result, the rate of forward and reverse reactions increases, but not to the same extent. A decrease in pressure according to a similar scheme leads to a decrease in the rates of forward and reverse reactions. But at the same time, the reaction rate, towards which the equilibrium shifts, decreases to a lesser extent.
The catalyst does not affect the equilibrium shift, because it speeds up (or slows down) both the forward and reverse reactions to the same extent. In its presence, chemical equilibrium is only established faster (or slower).
If a system is affected by several factors simultaneously, then each of them acts independently of the others. For example, in the synthesis of ammonia
N 2(gas) + 3H 2(gas) 2NH 3(gas)
the reaction is carried out by heating and in the presence of a catalyst to increase its speed. But the effect of temperature leads to the fact that the equilibrium of the reaction shifts to the left, towards the reverse endothermic reaction. This causes a decrease in the output of NH 3. To compensate for this undesirable effect of temperature and increase the yield of ammonia, the pressure in the system is simultaneously increased, which shifts the equilibrium of the reaction to the right, i.e. towards the formation of fewer gas molecules.
In this case, the most optimal conditions for the reaction (temperature, pressure) are selected experimentally, at which it would proceed at a sufficiently high speed and give an economically viable yield of the final product.
Le Chatelier's principle is similarly used in the chemical industry in the production of a large number of different substances of great importance for the national economy.
Le Chatelier's principle is applicable not only to reversible chemical reactions, but also to various other equilibrium processes: physical, physicochemical, biological.
The adult human body is characterized by the relative constancy of many parameters, including various biochemical indicators, including the concentrations of biologically active substances. However, such a state cannot be called equilibrium, because it is not applicable to open systems.
The human body, like any living system, constantly exchanges various substances with the environment: it consumes food and releases products of their oxidation and decay. Therefore, it is typical for an organism steady state, defined as the constancy of its parameters at a constant rate of exchange of matter and energy with the environment. To a first approximation, a stationary state can be considered as a series of equilibrium states interconnected by relaxation processes. In a state of equilibrium, the concentrations of substances participating in the reaction are maintained due to the replenishment of the initial products from the outside and the removal of the final products to the outside. A change in their content in the body does not lead, unlike closed systems, to a new thermodynamic equilibrium. The system returns to its original state. Thus, the relative dynamic constancy of the composition and properties of the internal environment of the body is maintained, which determines the stability of its physiological functions. This property of a living system is called differently homeostasis.
During the life of an organism in a stationary state, in contrast to a closed equilibrium system, an increase in entropy occurs. However, along with this, the reverse process also occurs simultaneously - a decrease in entropy due to the consumption of nutrients with a low entropy value from the environment (for example, high-molecular compounds - proteins, polysaccharides, carbohydrates, etc.) and the release of decomposition products into the environment. According to the position of I.R. Prigogine, the total production of entropy for an organism in a stationary state tends to a minimum.
A major contribution to the development of nonequilibrium thermodynamics was made by I. R. Prigozhy, Nobel Prize winner in 1977, who argued that “in any nonequilibrium system there are local areas that are in an equilibrium state. In classical thermodynamics, equilibrium refers to the entire system, but in nonequilibrium, only to its individual parts.”
It has been established that entropy in such systems increases during embryogenesis, during regeneration processes and the growth of malignant neoplasms.