Chemical equilibrium topic explanation. Chemical equilibrium. equilibrium shift

All chemical reactions are, in principle, reversible.
This means that both the interaction of reagents and the interaction of products occurs in the reaction mixture. In this sense, the distinction between reactants and products is conditional. The direction of a chemical reaction is determined by the conditions of its conduct (temperature, pressure, concentration of substances).
Many reactions have one preferential direction and to carry out such reactions in the opposite direction requires extreme conditions. In such reactions, almost complete conversion of reactants into products occurs.
Example. Iron and sulfur, when heated moderately, react with each other to form iron (II) sulfide; FeS is stable under such conditions and practically does not decompose into iron and sulfur:

At 200 atm and 400 0C, the maximum NH3 content in the reaction mixture is reached, equal to 36% (by volume). With a further increase in temperature, due to the increased occurrence of the reverse reaction, the volume fraction of ammonia in the mixture decreases.
Forward and reverse reactions occur simultaneously in opposite directions.

In all reversible reactions, the rate of the forward reaction decreases and the rate of the reverse reaction increases until both rates are equal and equilibrium is established.

In a state of equilibrium, the rates of forward and reverse reactions become equal.

LE CHATELIER'S PRINCIPLE. SHIFT OF CHEMICAL EQUILIBRIUM.

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 1884 by the French scientist Le Chatelier. The modern formulation of Le Chatelier's principle is as follows:

1. Effect of temperature. In each reversible reaction, one of the directions corresponds to an exothermic process, and the other to an endothermic process.

2. Effect of pressure. In all reactions involving gaseous substances, accompanied by a change in volume due to a change in the amount of substance during the transition from starting substances to products, the equilibrium position is affected by the pressure in the system.
The influence of pressure on the equilibrium position obeys the following rules:

Thus, during the transition from starting substances to products, the volume of gases was halved. This means that with increasing pressure, the equilibrium shifts towards the formation of NH3, as evidenced by the following data for the ammonia synthesis reaction at 400 0C:

3. Effect of concentration. The influence of concentration on the state of equilibrium is subject to the following rules:

>> Chemistry: Chemical equilibrium and methods for its displacement. In reversible processes, the rate of the direct reaction is initially maximum, and then decreases due to the fact that the concentrations of the starting substances consumed in the formation of reaction products decrease. On the contrary, the rate of the reverse reaction, minimal at the beginning, increases as the concentration of reaction products increases. Finally, a moment comes when the rates of the forward and reverse reactions become equal.

The state of a chemical reversible process is called chemical equilibrium if the rate of the forward reaction is equal to the rate of the reverse reaction.

Chemical equilibrium is dynamic (mobile), since when it occurs, the reaction does not stop, only the concentrations of the components remain unchanged, that is, per unit time the same amount of reaction products is formed as is converted into the starting substances. At constant temperature and pressure, the equilibrium of a reversible reaction can be maintained indefinitely.

In production, they are most often interested in the preferential occurrence of a direct reaction. For example, in the production of ammonia, sulfur oxide (VI). nitric oxide (II). How to derive a system from a state of equilibrium? How does a change in the external conditions under which this or that reversible chemical process occurs affect it?

Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year guidelines discussion programs Integrated Lessons

The chemical equilibrium in the reaction shifts towards the formation of the reaction product when

1) decrease in pressure

2) increasing temperature

3) adding a catalyst

4) adding hydrogen

Explanation.

Decreased pressure ( external influence) will lead to an intensification of pressure-increasing processes, which means that the equilibrium will shift towards more gaseous particles (which create pressure), i.e. towards the reagents.

When the temperature rises (external influence), the system will tend to lower the temperature, which means that the process of absorbing heat intensifies. the equilibrium will shift towards the endothermic reaction, i.e. towards the reagents.

The addition of hydrogen (external influence) will lead to an intensification of processes that consume hydrogen, i.e. the equilibrium will shift towards the reaction product

Answer: 4

Source: Yandex: Unified State Exam training work in chemistry. Option 1.

The equilibrium shifts towards the starting substances when

1) decreasing pressure

2) heating

3) introduction of a catalyst

4) adding hydrogen

Explanation.

Le Chatelier's principle - if a system in equilibrium is influenced from the outside by changing any of the equilibrium conditions (temperature, pressure, concentration), then processes in the system aimed at compensating for the external influence are enhanced.

A decrease in pressure (external influence) will lead to an intensification of processes that increase pressure, which means that the equilibrium will shift towards a larger number of gaseous particles (which create pressure), i.e. towards the reaction products.

The catalyst does not affect the equilibrium shift

The addition of hydrogen (external influence) will lead to an intensification of processes that consume hydrogen, i.e. the equilibrium will shift towards the starting substances

Answer: 4

Source: Yandex: Unified State Exam training work in chemistry. Option 2.

a shift of chemical equilibrium to the right will contribute to

1) decrease in temperature

2) increase in the concentration of carbon monoxide (II)

3) increase in pressure

4) reducing chlorine concentration

Explanation.

It is necessary to analyze the reaction and find out what factors will contribute to a shift in equilibrium to the right. The reaction is endothermic, occurs with an increase in the volume of gaseous products, is homogeneous, occurring in the gas phase. According to Le Chatelier's principle, a system has a reaction to an external action. Therefore, the equilibrium can be shifted to the right if the temperature is increased, the pressure is decreased, the concentration of the starting substances is increased, or the amount of reaction products is decreased. Having compared these parameters with the answer options, we select answer No. 4.

Answer: 4

Shift of chemical equilibrium to the left in a reaction

will contribute

1) reducing the concentration of chlorine

2) decreasing the concentration of hydrogen chloride

3) increase in pressure

4) decrease in temperature

Explanation.

The impact on a system in equilibrium is accompanied by resistance on its part. When the concentration of the starting substances decreases, the equilibrium shifts towards the formation of these substances, i.e. to the left.

Ekaterina Kolobova 15.05.2013 23:04

The answer is incorrect. It is necessary to reduce the temperature (as the temperature decreases, the equilibrium will shift towards exothermic evolution)

Alexander Ivanov

As the temperature decreases, the equilibrium will shift towards exothermic release, i.e. to the right.

So the answer is correct

A. When using a catalyst, there is no shift in the chemical equilibrium in this system.

B. As the temperature increases, the chemical equilibrium in this system will shift towards the starting substances.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

When using a catalyst, a shift in the chemical equilibrium in this system does not occur, because The catalyst accelerates both forward and reverse reactions.

As the temperature increases, the chemical equilibrium in this system will shift towards the starting substances, because the reverse reaction is endothermic. Increasing the temperature in the system leads to an increase in the rate of the endothermic reaction.

Answer: 3

will shift towards the opposite reaction if

1) increase blood pressure

2) add a catalyst

3) reduce concentration

4) increase the temperature

Explanation.

The chemical equilibrium in the system will shift towards the reverse reaction if the rate of the reverse reaction is increased. We reason as follows: the reverse reaction is an exothermic reaction that occurs with a decrease in the volume of gases. If you reduce the temperature and increase the pressure, the equilibrium will shift towards the opposite reaction.

Answer: 1

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. As the temperature decreases, the chemical equilibrium in a given system shifts

towards the reaction products.

B. When the methanol concentration decreases, the equilibrium in the system shifts towards the reaction products.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

As the temperature decreases, the chemical equilibrium in a given system shifts

towards the reaction products this is true, because the direct reaction is exothermic.

When the methanol concentration decreases, the equilibrium in the system shifts towards the reaction products, this is true because when the concentration of a substance decreases, the reaction as a result of which this substance is formed occurs faster

Answer: 3

In which system does a change in pressure have virtually no effect on the shift in chemical equilibrium?

Explanation.

To prevent equilibrium from shifting to the right when pressure changes, it is necessary that the pressure in the system does not change. Pressure depends on the amount of gaseous substances in a given system. Let's calculate the volumes of gaseous substances on the left and right sides of the equation (using coefficients).

This will be reaction number 3

Answer: 3

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. When the pressure decreases, the chemical equilibrium in this system will shift

towards the reaction product.

B. With increasing concentration carbon dioxide the chemical equilibrium of the system will shift towards the reaction product.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

The addition of carbon dioxide (external influence) will lead to an intensification of processes that consume carbon dioxide, i.e., the equilibrium will shift towards the reagents. Statement B is incorrect.

Answer: both statements are incorrect.

Answer: 4

Chemical equilibrium in the system

shifts towards the starting substances as a result

1) increasing the concentration of hydrogen

2) temperature rise

3) increase in pressure

4) use of a catalyst

Explanation.

The direct reaction is exothermic, the reverse reaction is endothermic, therefore, as the temperature increases, the equilibrium will shift towards the starting substances.

Answer: 2

Explanation.

In order for the equilibrium to shift to the right when the pressure increases, it is necessary that the direct reaction occurs with a decrease in the volume of gases. Let's calculate the volumes of gaseous substances. on the left and right sides of the equation.

This will be reaction number 3

Answer: 3

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. As the temperature increases, the chemical equilibrium in this system will shift

towards the reaction products.

B. When the concentration of carbon dioxide decreases, the equilibrium of the system will shift towards the reaction products.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

The forward reaction is exothermic, the reverse reaction is endothermic, therefore, as the temperature increases, the equilibrium will shift towards the reverse reaction. (the first statement is false)

With an increase in the concentration of the starting substances, the equilibrium will shift towards the forward reaction; with an increase in the concentration of the reaction products, the equilibrium will shift towards the reverse reaction. When the concentration of a substance decreases, the reaction as a result of which this substance is formed occurs faster. (second statement is true)

Answer: 2

Anton Golyshev

No - the explanation is written correctly, read more carefully. As the concentration of carbon dioxide decreases, the equilibrium will shift towards the reaction of its formation - towards the products.

Lisa Korovina 04.06.2013 18:36

The assignment says:

B. As the concentration of carbon dioxide decreases, the equilibrium of the system will shift towards the reaction products... As I understand it, Right side in a reaction, these are the reaction products. It follows that both options are correct!

Alexander Ivanov

It follows that the second statement is true.

In system

A shift of chemical equilibrium to the left will occur when

1) decrease in pressure

2) decreasing temperature

3) increasing oxygen concentration

4) adding a catalyst

Explanation.

Let's calculate the amount of gaseous products in the right and left sides of the reaction (using coefficients).

3 and 2. From this we can see that if the pressure is lowered, then the equilibrium will shift to the left, because the system strives to restore equilibrium in the system.

Answer: 1

In system

1) increase in pressure

2) increase in the concentration of carbon monoxide (IV)

3) decrease in temperature

4) increase in oxygen concentration

Explanation.

An increase in pressure (external influence) will lead to an intensification of processes that reduce pressure, which means that the equilibrium will shift towards a smaller number of gaseous particles (which create pressure), i.e. towards the reaction products.

The addition of carbon monoxide (IV) (external influence) will lead to an intensification of processes that consume carbon monoxide (IV), i.e. the equilibrium will shift towards the starting substances

When the temperature decreases (external influence), the system will tend to increase the temperature, which means that the process that releases heat intensifies. The equilibrium will shift towards the exothermic reaction, i.e. towards the reaction products.

The addition of oxygen (external influence) will lead to an increase in processes that consume oxygen, i.e. the equilibrium will shift towards the reaction products.

Answer: 2

A. When the temperature increases in this system, the chemical equilibrium does not shift,

B. As the hydrogen concentration increases, the equilibrium in the system shifts towards the starting substances.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

According to Le Chatelier’s rule, since heat is released in a direct reaction, when it increases, the equilibrium will shift to the left; Also, since hydrogen is a reagent, when the hydrogen concentration increases, the equilibrium in the system shifts towards the products. Thus, both statements are incorrect.

Answer: 4

In system

a shift in chemical equilibrium towards the formation ester will contribute

1) adding methanol

2) increase in pressure

3) increasing the concentration of ether

4) adding sodium hydroxide

Explanation.

When adding (increasing the concentration) of any starting substance, the equilibrium shifts towards the reaction products.

Answer: 1

In which system, as the pressure increases, will the chemical equilibrium shift towards the starting substances?

Explanation.

An increase or decrease in pressure can shift the equilibrium only in processes in which gaseous substances participate and which occur with a change in volume.

To shift the equilibrium towards the starting substances with increasing pressure, conditions are necessary for the process to proceed with an increase in volume.

This is process 2. (Starting substances are 1 volume, reaction products are 2)

Answer: 2

In which system does an increase in hydrogen concentration shift the chemical equilibrium to the left?

Explanation.

If an increase in hydrogen concentration shifts the chemical equilibrium to the left, then we're talking about about hydrogen as a reaction product. The reaction product is hydrogen only in option 3.

Answer: 3

In system

A shift in chemical equilibrium to the right is facilitated by

1) increase in temperature

2) decrease in pressure

3) increase in chlorine concentration

4) reducing the concentration of sulfur oxide (IV)

Explanation.

An increase in the concentration of any of the starting substances shifts the chemical equilibrium to the right.

Answer: 3

a shift in chemical equilibrium towards the starting substances will contribute to

1) decrease in pressure

2) decrease in temperature

3) increase in concentration

4) decrease in concentration

Explanation.

This reaction proceeds with a decrease in volume. As the pressure decreases, the volume increases, therefore, the equilibrium shifts towards increasing volume. In this reaction towards the starting substances, i.e. to the left.

Answer: 1

Alexander Ivanov

If you decrease the SO 3 concentration, the equilibrium will shift towards the reaction that increases the SO 3 concentration, that is, to the right (towards the reaction product)

Chemical equilibrium in the system

shifts to the right when

1) increasing pressure

2) decreasing temperature

3) increasing concentration

4) increasing temperature

Explanation.

With an increase in pressure, a decrease in temperature or an increase in concentration, the equilibrium, according to Le Chatelier's rule, will shift to the left, only with an increase in temperature will the equilibrium shift to the right.

Answer: 4

On the state of chemical equilibrium in the system

does not affect

1) increase in pressure

2) increase in concentration

3) increase in temperature

4) decrease in temperature

Explanation.

Since this is a homogeneous reaction not accompanied by a change in volume, an increase in pressure does not affect the state of chemical equilibrium in this system.

Answer: 1

In which system, as the pressure increases, will the chemical equilibrium shift towards the starting substances?

Explanation.

According to Le Chatelier's rule, with increasing pressure the chemical equilibrium will shift towards the starting substances in a homogeneous reaction, accompanied by an increase in the number of moles of gaseous products. There is only one such reaction - number two.

Answer: 2

On the state of chemical equilibrium in the system

does not affect

1) increase in pressure

2) increase in concentration

3) increase in temperature

4) decrease in temperature

Explanation.

Changes in temperature and concentration of substances will affect the state of chemical equilibrium. In this case, the amount of gaseous substances on the left and right is the same, therefore, even though the reaction occurs with the participation of gaseous substances, an increase in pressure will not affect the state of chemical equilibrium.

Answer: 1

Chemical equilibrium in the system

shifts to the right when

1) increasing pressure

2) increasing concentration

3) lowering the temperature

4) increasing temperature

Explanation.

Since this is not a homogeneous reaction, a change in pressure will not affect it; an increase in the concentration of carbon dioxide will shift the equilibrium to the left. Since heat is absorbed in a direct reaction, its increase will lead to a shift of equilibrium to the right.

Answer: 4

In which system does a change in pressure have virtually no effect on the shift in chemical equilibrium?

Explanation.

In the case of homogeneous reactions, a change in pressure has virtually no effect on the shift in chemical equilibrium in systems in which there is no change in the number of moles of gaseous substances during the reaction. IN in this case This is reaction number 3.

Answer: 3

In the system, a shift in chemical equilibrium towards the starting substances will be facilitated by

1) decrease in pressure

2) decrease in temperature

3) decrease in concentration

4) increase in concentration

Explanation.

Since this reaction is homogeneous and is accompanied by a decrease in the number of moles of gaseous substances, as the pressure decreases, the equilibrium in this system will shift to the left.

Answer: 1

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. When pressure increases, the chemical equilibrium shifts towards the reaction product.

B. When the temperature decreases, the chemical equilibrium in this system will shift towards the reaction product.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

Since this is a homogeneous reaction, accompanied by a decrease in the number of moles of gases, with increasing pressure the chemical equilibrium shifts towards the reaction product. In addition, when a direct reaction occurs, heat is released, so when the temperature decreases, the chemical equilibrium in this system will shift towards the reaction product. Both judgments are correct.

Answer: 3

In system

a shift of chemical equilibrium to the right will occur when

1) increasing pressure

2) increasing temperature

3) increasing the concentration of sulfur oxide (VI)

4) adding a catalyst

Explanation.

The amount of gaseous substances in this system on the left is greater than on the right, that is, when a direct reaction occurs, the pressure decreases, so an increase in pressure will cause a shift in the chemical equilibrium to the right.

Answer: 1

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. As the temperature increases, the chemical equilibrium in this system will shift towards the starting substances.

B. With an increase in the concentration of nitric oxide (II), the equilibrium of the system will shift towards the starting substances.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

Since heat is released in this system, according to Le Chatelier’s rule, with increasing temperature, the chemical equilibrium in this system will actually shift towards the starting substances. Since nitric oxide (II) is a reactant, as its concentration increases, the equilibrium will shift towards the products.

Answer: 1

Are the following judgments about the shift in chemical equilibrium in the system correct?

A. As the temperature decreases, the chemical equilibrium in this system will shift towards the reaction products.

B. When the concentration of carbon monoxide decreases, the equilibrium of the system will shift towards the reaction products.

1) only A is correct

2) only B is correct

3) both judgments are correct

4) both judgments are incorrect

Explanation.

In this reaction, heat is released, so as the temperature decreases, the chemical equilibrium in this system will actually shift towards the reaction products. Since carbon monoxide is a reagent, a decrease in its concentration will cause a shift in the equilibrium towards its formation - that is, towards the reagents.

Answer: 1

In system

a shift in chemical equilibrium to the right will occur when

1) increasing pressure

2) increasing temperature

3) increasing the concentration of sulfur oxide (VI)

4) adding a catalyst

Explanation.

In this homogeneous reaction, the number of moles of gaseous substances decreases, so a shift of chemical equilibrium to the right will occur with increasing pressure.

Answer: 1

Chemical equilibrium in the system

shifts to the right when

1) increasing pressure

2) increasing concentration

3) lowering the temperature

4) increasing temperature

Explanation.

With increasing pressure, increasing concentration or decreasing temperature, the equilibrium will shift towards a decrease in these effects - that is, to the left. And since the reaction is endothermic, only with increasing temperature will the equilibrium shift to the right.

Answer: 4

As the pressure increases, the yield of product(s) in a reversible reaction will decrease

1) N 2 (g) + 3H 2 (g) 2NH 3 (g)

2) C 2 H 4 (g) + H 2 O (g) C 2 H 5 OH (g)

3) C (tv) + CO 2 (g) 2CO (g)

4) 3Fe (tv) + 4H 2 O (g) Fe 3 O 4 (tv) + 4H 2 (g)

Explanation.

According to Le Chatelier’s principle, if a system in a state of chemical equilibrium is influenced from the outside by changing any of the equilibrium conditions (temperature, pressure, concentration), then the equilibrium in the system will shift in the direction that reduces the influence.

Here we need to find a reaction in which the equilibrium will shift to the left as the pressure increases. In this reaction, the number of moles of gaseous substances on the right must be greater than on the left. This is reaction number 3.

Answer: 3

shifts towards the reaction products when

1) decreasing temperature

2) decrease in pressure

3) using a catalyst

4) increasing temperature

Explanation.

The equilibrium of an endothermic reaction will shift to the right as the temperature increases.

Answer: 4

Source: Unified State Exam in Chemistry 06/10/2013. Main wave. Far East. Option 2.

REACTION EQUATION

2) towards the starting substances

3) practically does not move

A	B	IN	G

Explanation.

A) 1) towards the reaction products

Answer: 1131

Establish a correspondence between the equation of a chemical reaction and the direction of displacement of the chemical equilibrium with increasing pressure in the system:

REACTION EQUATION

DIRECTION OF CHEMICAL EQUILIBRIUM SHIFT

1) towards the reaction products

2) towards the starting substances

3) practically does not move

Write down the numbers in your answer, arranging them in the order corresponding to the letters:

A	B	IN	G

Explanation.

As pressure increases, the equilibrium will shift towards fewer gases.

A) - towards the reaction products (1)

B) - towards the reaction products (1)

B) - towards the starting substances (2)

D) - towards the reaction products (1)

Answer: 1121

Establish a correspondence between the equation of a chemical reaction and the direction of displacement of the chemical equilibrium with increasing pressure in the system:

REACTION EQUATION

DIRECTION OF CHEMICAL EQUILIBRIUM SHIFT

1) towards the reaction products

2) towards the starting substances

3) practically does not move

Write down the numbers in your answer, arranging them in the order corresponding to the letters:

A	B	IN	G

Explanation.

As the pressure increases, the equilibrium will shift towards the reaction with less gaseous substances.

B) 2) towards the starting substances

B) 3) practically does not move

D) 1) towards the reaction products

Answer: 2231

Establish a correspondence between the equation of a chemical reaction and the direction of displacement of the chemical equilibrium with increasing pressure in the system:

REACTION EQUATION

DIRECTION OF CHEMICAL EQUILIBRIUM SHIFT

1) towards the reaction products

2) towards the starting substances

3) practically does not move

Write down the numbers in your answer, arranging them in the order corresponding to the letters:

A	B	IN	G

Explanation.

As the pressure increases, the equilibrium will shift towards the reaction with less gaseous substances.

A) 2) towards the starting substances

B) 1) towards the reaction products

B) 3) practically does not move

D) 2) towards the starting substances

Answer: 2132

Establish a correspondence between the equation of a chemical reaction and the direction of displacement of the chemical equilibrium when the pressure in the system decreases:

REACTION EQUATION

DIRECTION OF CHEMICAL EQUILIBRIUM SHIFT

1) towards the reaction products

2) towards the starting substances

3) practically does not move

Write down the numbers in your answer, arranging them in the order corresponding to the letters:

A	B	IN	G

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 maximum speed, which gradually decreases due to a decrease in the number of reagents. The reverse reaction, on the contrary, initially has 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 straightυ 1 and reverseυ 2 reactions:

v1 = k 1 ·[A] a ·[B] b

v2 = k 2 ·[C] c ·[D] d

Able 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 does not affect 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 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.

Most chemical reactions are reversible, that is, they occur simultaneously in opposite directions. In cases where the forward and reverse reactions proceed at the same rate, chemical equilibrium occurs.

When chemical equilibrium occurs, the number of molecules of substances that make up the system stops changing and remains constant over time under constant external conditions.

The state of the system in which the rate of the forward reaction is equal to the rate of the reverse reaction is called chemical equilibrium.

For example, the equilibrium of the reaction H 2 (g) + I 2 (g) ⇆ 2HI (g) occurs when exactly the same number of hydrogen iodide molecules are formed per unit time by the direct reaction as they are decomposed by the reverse reaction into iodine and hydrogen.

The ability of a reaction to proceed in opposite directions is called kinetic reversibility.

In a reaction equation, reversibility is indicated by two opposite arrows (⇆) instead of an equal sign between the left and right sides of the chemical equation.

Chemical equilibrium is dynamic (mobile). When external conditions change, the equilibrium shifts and returns to its original state if external conditions acquire constant values. The influence of external factors on the chemical equilibrium causes its displacement.

The position of chemical equilibrium depends on the following reaction parameters:

Temperatures;

Pressure;

Concentrations.

The influence that these factors have on a chemical reaction is subject to a pattern that was expressed in general terms in 1884 by the French scientist Le Chatelier (Fig. 1).

Rice. 1. Henri Louis Le Chatelier

Modern formulation of Le Chatelier's principle

If an external influence is exerted on a system that is in equilibrium, then the equilibrium shifts to the side that weakens this influence.

1. Effect of temperature

In each reversible reaction, one of the directions corresponds to an exothermic process, and the other to an endothermic process.

Example: industrial production ammonia. Rice. 2.

Rice. 2. Ammonia production plant

Ammonia synthesis reaction:

N 2 + 3H 2 ⇆ 2NH 3 + Q

The forward reaction is exothermic, and the reverse reaction is endothermic.

The effect of temperature changes on the position of chemical equilibrium obeys the following rules.

As the temperature increases, the chemical equilibrium shifts in the direction of the endothermic reaction, and as the temperature decreases, in the direction of the exothermic reaction.

To shift the equilibrium towards the production of ammonia, the temperature must be lowered.

2. Effect of pressure

In all reactions involving gaseous substances, accompanied by a change in volume due to a change in the amount of substance during the transition from starting substances to products, the equilibrium position is influenced by the pressure in the system.

The influence of pressure on the equilibrium position obeys the following rules.

With increasing pressure, the equilibrium shifts towards the formation of substances (initial or products) with a smaller volume; as pressure decreases, the equilibrium shifts towards the formation of substances with a larger volume.

In the reaction of ammonia synthesis, with increasing pressure, the equilibrium shifts towards the formation of ammonia, because the reaction proceeds with a decrease in volume.

3. Effect of concentration

The influence of concentration on the state of equilibrium is subject to the following rules.

When the concentration of one of the starting substances increases, the equilibrium shifts towards the formation of reaction products; When the concentration of one of the reaction products increases, the equilibrium shifts towards the formation of the starting substances.

In the reaction producing ammonia, in order to shift the equilibrium towards the production of ammonia, it is necessary to increase the concentration of hydrogen and nitrogen.

Summing up the lesson

In the lesson, you learned about the concept of “chemical equilibrium” and how to shift it, what conditions affect the displacement of chemical equilibrium and how the “Le Chatelier principle” works.

Bibliography

Novoshinsky I.I., Novoshinskaya N.S. Chemistry. Textbook for 10th grade general education. establishment Profile level. - M.: LLC "TID" Russian word- RS", 2008. (§§ 24, 25)
Kuznetsova N.E., Litvinova T.N., Levkin A.N. Chemistry: 11th grade: Textbook for general education students. establishment ( profile level): in 2 parts. Part 2. M.: Ventana-Graf, 2008. (§ 24)
Rudzitis G.E. Chemistry. Fundamentals of general chemistry. 11th grade: educational. for general education establishment: a basic level of/ G.E. Rudzitis, F.G. Feldman. - M.: Education, OJSC “Moscow Textbooks”, 2010. (§ 13)
Radetsky A.M. Chemistry. Didactic material. 10-11 grades. - M.: Education, 2011. (p. 96-98)
Khomchenko I.D. Collection of problems and exercises in chemistry for high school. - M.: RIA “New Wave”: Publisher Umerenkov, 2008. (p. 65-68)

Hemi.nsu.ru ().
Alhimikov.net ().
Prosto-o-slognom.ru ().

Homework

With. 65-66 No. 12.10-12.17 from the Collection of problems and exercises in chemistry for secondary school (Khomchenko I.D.), 2008.
In what case will a change in pressure not cause a shift in the chemical equilibrium in reactions involving gaseous substances?
Why does the catalyst not shift the chemical equilibrium?