With a decrease in the concentration of products, the equilibrium will shift. Chemical equilibrium shift

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 a chemical reaction obeys a pattern that was expressed in general view in 1885 by the French scientist Le Chatelier.

Factors affecting chemical equilibrium:

1) temperature

With an increase in temperature, chemical equilibrium shifts towards the endothermic (absorption) reaction, and with a decrease in the direction of an exothermic (release) reaction.

CaCO 3 = CaO + CO 2 -Q t →, t ↓ ←

N 2 + 3H 2 ↔2NH 3 + Q t ←, t ↓ →

2) pressure

With an increase in pressure, chemical equilibrium shifts towards a smaller volume of substances, and with a decrease in the direction of 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 ↓ →

1 mol = 1 mol + 1 mol

3) concentration of starting substances and reaction products

With an increase in the concentration of one of the initial substances, the chemical equilibrium shifts towards the reaction products, and with an increase in the concentration of the reaction products, towards the initial substances.

S 2 + 2O 2 = 2SO 2 [S], [O] →, ←

The catalysts do not affect the shift in chemical equilibrium!

Basic quantitative characteristics of chemical equilibrium: chemical equilibrium constant, degree of conversion, degree of dissociation, equilibrium yield. Explain the meaning of these values ​​using the example of specific chemical reactions.

In chemical thermodynamics, the law of the active masses connects the equilibrium activities of the initial substances and reaction products, according to the ratio:

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 (for initial substances it is taken negative, for products - positive);

Chemical equilibrium constant. The subscript "a" here means the use of the activity value in the formula.

The effectiveness of the reaction carried out is usually evaluated by calculating the yield of the reaction product (paragraph 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 turned into the target reaction product, for example, what part of SO 2 turned into SO 3 during the production of sulfuric acid, that is, find conversion rate starting material.

Let a short 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 proreag (A) - the amount of reagent substance A that reacted with the formation of product B, and n initial (A) - initial amount of reagent A.

Naturally, the degree of conversion can be expressed not only in terms of the amount of a substance, but also in terms of 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

An exception is reactions in which the initial substance is deliberately consumed for the formation of several products. So, for example, in the reaction

Cl 2 + 2KOH = KCl + KClO + H 2 O

chlorine (reagent) is equally converted to potassium chloride and potassium hypochlorite. In this reaction, even at a 100% yield of KClO, the degree of conversion of chlorine into it is 50%.

The quantity you know - the degree of protolysis (paragraph 12.4) - is a special case of the degree of conversion:

Within the framework of the 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 in accordance with the Ostwald dilution law.

Within the framework of the same theory, the hydrolysis equilibrium is characterized by degree of hydrolysis (h), in this case, the following expressions are used, connecting it with the initial concentration of the substance ( with) and dissociation constants of weak acids (K HA) and weak bases ( K MOH):

The first expression is valid for the hydrolysis of a salt of a weak acid, the second, for a salt of a weak base, and the third, for a salt of a weak acid and a weak base. All these expressions can be used only for dilute solutions with a degree of hydrolysis of no more than 0.05 (5%).

Usually, the equilibrium yield is determined by the known equilibrium constant, with which it is associated in each specific case by a certain ratio.

The product yield can be changed by shifting the equilibrium of the reaction in reversible processes, by the influence of factors such as temperature, pressure, concentration.

In accordance with Le Chatelier's principle, the equilibrium degree of conversion increases with increasing pressure in the course of simple reactions, while in other cases the volume of the reaction mixture does not change and the product yield does not depend on pressure.

The influence of temperature on the equilibrium yield, as well as on the equilibrium constant, is determined by the sign of the heat effect of the reaction.

For a more complete assessment of reversible processes, the so-called yield from the theoretical (yield from equilibrium) is used, which is equal to the ratio of the actually obtained product c to the amount that would have been obtained in a state of equilibrium.

THERMAL DISSOCIATION chemical

the reaction of reversible decomposition of a substance caused by an increase in temperature.

When so, from one substance, several (2H2H + OCaO + CO) or one simpler

The equilibrium of etc. is established according to the law of the acting masses. It

can be characterized either by an equilibrium constant or by the degree of dissociation

(the ratio of the number of disintegrated molecules to the total number of molecules). V

in most cases, etc. are accompanied by heat absorption (an increment

enthalpy

DN> 0); therefore, in accordance with the Le Chatelier-Brown principle

heating enhances it, the degree of displacement, etc., with temperature is determined

the absolute value of the DN. The pressure hinders the etc., the more the more

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.

e. solid substances (oxides, crystalline hydrates, etc.)

it's important to know

temperature, at which the dissociation pressure becomes equal to the external one (in particular,

atmospheric) pressure. Since the evolved gas 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 (an increase in temperature leads to an increase in the kinetic energy of dissolved particles, which contributes to the decomposition of molecules into ions)

Conversion of starting materials and equilibrium product yield. Methods for calculating them at a given temperature. What data is required 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 reagent reacted relative to its initial amount. For the simplest reaction, where is the concentration at the inlet to the reactor or at the beginning of a batch process, is the concentration at the outlet of the reactor or the current moment of the batch process. For an arbitrary reaction, for example , in accordance with the definition, the calculation formula is the same:. If there are several reagents in the reaction, then the degree of conversion can be considered 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 on time. At the initial moment of time, when nothing has changed, the degree of conversion is zero. Then, as the reagent is converted, the conversion increases. For an irreversible reaction, when nothing prevents the reagent from being consumed completely, its value tends (Fig. 1) to unity (100%). Fig.1 The higher the rate of consumption of the reagent, determined by the value of the rate constant, the faster the degree of conversion grows, which is shown in the figure. If the reaction is reversible, then as the reaction tends to equilibrium, the degree of conversion tends to an 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 The yield of the product is the amount of actually obtained target product, referred to the amount of this product, which would have been obtained if all the reagent had passed into this product (to the maximum possible amount of the resulting product). Or (via the reagent): the amount of the reagent actually transferred to the target product, referred to the initial amount of the reagent. For the simplest reaction, the output, and bearing in mind that for this reaction, , i.e. for the simplest reaction, the yield and conversion are one and 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 should be included in the calculated expression. In accordance with the first definition, the imaginary amount of the product obtained from the entire initial amount of the reagent will be two times less for this reaction than the initial amount of the reagent, i.e. , and calculation formula... In accordance with the second definition, the amount of reagent actually transferred to the target product will be twice as much as the amount of this product formed, i.e. , then the calculation formula. 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 a reaction, ... If there are several reagents in the reaction, the yield can be calculated for each of them; if, in addition, there are several target products, then the yield can be considered for any target product for any reagent. As can be seen from the structure of the calculation formula (there is a constant in the denominator), the dependence of the yield on the reaction time is determined by the dependence on the time of the concentration of the target product. So, for example, for the reaction this dependence looks like in Fig. 3. Fig. 3

Conversion degree 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 the justification for the answer and the corresponding mathematical expressions.

To determine dependence K 0 on temperature in differential form, we use the Gibbs-Helmholtz equation (III, 41)

and equation (V, 11)

Combining the above equations, we get

or (V, 12)

Equation (V, 12) is called the Van't Hoff equation or isobar reaction equation(the process is carried out at P = const).

For a small temperature range T 1 T 2 the thermal effect of the reaction can be assumed constant. After integration, taking into account the assumption made, equation (V, 12) takes the form

(V, 13)

Expression (V, 13) allows you to calculate the equilibrium constant at one of the temperatures, if you know its value at another temperature, as well as the thermal effect of the reaction.

With indefinite integration of Eq. (V, 12), we obtain

(V, 14)

where V- constant of integration.

According to Eq. (V, 14), the dependence ln K 0 from the reciprocal temperature is expressed by a straight line, the slope of which is equal to.

This method of calculating the heat effect is usually used if its direct determination (or calculation according to Hess's law) is difficult, for example, in cases where the reaction is carried out only at high temperatures.

According to equation (V, 14), the influence of temperature on the equilibrium constant is determined by the sign of the thermal effect.

If D H 0> 0 (endothermic process), then in coordinates ln K 0 - the tangent of the angle of inclination of the straight line will have a negative value (the angle of inclination is obtuse), therefore, with increasing temperature, the constant will increase, i.e., the chemical equilibrium is shifted towards the reaction products (see Fig. 19).

Rice. 19. Dependence of the logarithm of the equilibrium constant of the endothermic reaction on the reciprocal temperature (D H 0 > 0).

When D H 0 < 0 (экзотермическая реакция) тангенс угла наклона прямой будет иметь положительное значение (угол наклона - острый). С повышением температуры константа равновесия будет уменьшаться и химическое равновесие смещается в сторону исходных веществ (смотри рис.20).

Rice. 20. Dependence of the logarithm of the equilibrium constant of an exothermic reaction on the reciprocal temperature (D H 0 < 0)

§ 7. Le Chatelier-Brown principle

The system, taken out of the state of equilibrium, again returns to the state of equilibrium. Le Chatelier and Brown put forward a simple principle that can be used to predict in which direction a system will respond to a disturbance that throws it out of equilibrium.

Le Chatelier formulated this principle as follows:

"Any system in equilibrium undergoes, as a result of a change in one of the factors governing equilibrium, a compensating change in such a direction that, if this change were the only one, it would cause a change in the factor in question in the opposite direction."

As an example, consider the equilibrium

N 2 + 3H 2 «2 NH 3

In this reaction, when the reactants are converted into products, the number of moles decreases, which leads to a decrease in pressure at a fixed temperature. If in such a system, which is in a state of equilibrium, suddenly increase the pressure, then the system will react to such a disturbance by production more NH 3, causing the pressure to drop. The compensating change in the system will occur in the opposite direction to the disturbance. The new state of equilibrium will have more NH 3. The ammonia synthesis reaction is exothermic. Consequently, if heat is supplied to the system, then the equilibrium will shift towards the formation of the initial substances, and the content NH 3 in the equilibrium mixture will decrease.

(Note that we have already discussed the nature of the influence of pressure and temperature on equilibrium earlier (see §§4 and 6, chapter V.) in the form of the principle formulated by them).

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

1) lowering pressure

2) rise in temperature

3) adding catalyst

4) adding hydrogen

Explanation.

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 reagents.

As the temperature rises (external influence), the system will tend to lower the temperature, which means that the process of absorbing heat is intensified. 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 the processes that consume hydrogen, i.e. the equilibrium will shift towards the reaction product

Answer: 4

Source: Yandex: Training work of the exam in chemistry. Option 1.

The equilibrium shifts towards the starting substances when

1) decrease in pressure

2) heating

3) the introduction of the catalyst

4) adding hydrogen

Explanation.

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

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.

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

Catalyst does not affect equilibrium displacement

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

Answer: 4

Source: Yandex: Training work of the exam in chemistry. Option 2.

a shift in chemical equilibrium to the right will contribute

1) decrease in temperature

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

3) increase in pressure

4) decrease in chlorine concentration

Explanation.

It is necessary to analyze the reaction and find out what factors will contribute to the shift of the balance to the right. The reaction is endothermic, proceeds with an increase in the volume of gaseous products, homogeneous, proceeding in the gas phase. According to Le Chatelier's principle, the system has a reaction to the external action. Therefore, the equilibrium can be shifted to the right by increasing the temperature, decreasing the pressure, increasing the concentration of the starting materials, or decreasing the amount of reaction products. Comparing these parameters with the answer options, choose the answer number 4.

Answer: 4

Shifting chemical equilibrium to the left in a reaction

will contribute to

1) decrease in chlorine concentration

2) a decrease in the concentration of hydrogen chloride

3) increase in pressure

4) decrease in temperature

Explanation.

The impact on the system, which is in equilibrium, is accompanied by opposition from its side. With a decrease in the concentration of the starting substances, 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 (with decreasing temperature, the equilibrium will shift towards exothermic release)

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, a shift in the chemical equilibrium in this system does not occur.

B. With an increase in temperature, the chemical equilibrium in this system will shift towards the initial substances.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

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

With an increase in temperature, the chemical equilibrium in this system will shift towards the initial substances, because the reverse reaction is endothermic. An increase in temperature in the system leads to an increase in the rate of endothermic reaction.

Answer: 3

will shift in the direction of the reverse reaction if

1) increase the pressure

2) add catalyst

3) reduce concentration

4) increase the temperature

Explanation.

The chemical equilibrium in the system will shift in the direction of the reverse reaction if the rate of the reverse reaction is increased. We argue as follows: the reverse reaction is an exothermic reaction that occurs with a decrease in the volume of gases. If the temperature decreases and the pressure increases, the equilibrium will shift in the direction of the reverse reaction.

Answer: 1

Are the following judgments about the shift of chemical equilibrium in the system true?

A. With decreasing temperature, the chemical equilibrium in a given system shifts

towards the reaction products.

B. With a decrease in the concentration of methanol, the equilibrium in the system shifts towards the reaction products.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

With a decrease in temperature, the chemical equilibrium in a given system shifts

in the direction of reaction products, this is true, since direct reaction is exothermic.

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

Answer: 3

In which system, the change in pressure practically does not affect the shift in chemical equilibrium

Explanation.

So that when the pressure changes, the equilibrium does not shift to the right, it is necessary that the pressure in the system does not change. The pressure depends on the amount of gaseous substances in the system. Let's calculate the volumes of gaseous substances in the left and right sides equations (by coefficients).

This will be reaction # 3

Answer: 3

Are the following judgments about the shift of chemical equilibrium in the system true?

A. With decreasing pressure, 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 true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

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

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

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

Answer: both judgments are wrong.

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) pressure rise

4) using a catalyst

Explanation.

The direct reaction is exothermic, the reverse is endothermic, therefore, with an increase in temperature, the equilibrium will shift towards the starting substances.

Answer: 2

Explanation.

In order for the equilibrium to shift to the right with increasing pressure, it is necessary that the direct reaction proceeds 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 # 3

Answer: 3

Are the following judgments about the shift of chemical equilibrium in the system true?

A. As the temperature rises, the chemical equilibrium in a given system will shift

towards the reaction products.

B. With a decrease in the concentration of carbon dioxide, the equilibrium of the system will shift towards the reaction products.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

The direct reaction is exothermic, the reverse is endothermic, therefore, with an increase in temperature, the equilibrium will shift in the direction of the reverse reaction. (first statement is false)

With an increase in the concentration of the starting substances, the equilibrium will shift towards the direct reaction; with an increase in the concentration of the reaction products, the equilibrium will shift towards the reverse reaction. With a decrease in the concentration of a substance, the reaction proceeds faster, as a result of which this substance is formed. (the second statement is correct)

Answer: 2

Anton Golyshev

No - the explanation is written correctly, read carefully. With a decrease in the concentration of carbon dioxide, the equilibrium will shift towards the reaction of its formation - towards the products.

Liza Korovina 04.06.2013 18:36

In the task they write:

B. With a decrease in the concentration of carbon dioxide, the equilibrium of the system will shift towards the reaction products ... As I understand it, the right side in the reaction is the reaction products. Hence it follows - both options are correct!

Alexander Ivanov

Hence it follows that the second statement is true.

In system

A shift of chemical equilibrium to the left will occur when

1) lowering pressure

2) lowering the temperature

3) an increase in oxygen concentration

4) adding catalyst

Explanation.

Let's count the number gaseous products in the right and left parts of the reaction (by coefficients).

3 and 2. From this it can be seen that if the pressure is reduced, then the equilibrium will shift to the left, since the system seeks to restore balance in the system.

Answer: 1

In system

1) increase in pressure

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

3) decrease in temperature

4) an increase in oxygen concentration

Explanation.

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

An increase in pressure (external influence) will lead to an intensification of the 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 intensification of processes consuming carbon monoxide (IV), i.e. the equilibrium will shift towards the starting materials

With a decrease in temperature (external influence), the system will tend to increase the temperature, which means that the process of generating heat is intensified. The equilibrium will shift towards an exothermic reaction, i.e. towards the reaction products.

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

Answer: 2

A. With an increase in temperature in a given system, a shift in chemical equilibrium does not occur,

B. With an increase in the concentration of hydrogen, the equilibrium in the system shifts towards the initial substances.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

According to Le Chatelier's rule, since heat is released in a direct reaction, then with its increase the equilibrium will shift to the left; also, since hydrogen is a reagent, with an increase in hydrogen concentration, the equilibrium in the system shifts towards the products. Thus, both statements are wrong.

Answer: 4

In system

shift of chemical equilibrium towards formation ester will contribute to

1) adding methanol

2) pressure increase

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, with increasing pressure, the chemical equilibrium will shift towards the starting substances?

Explanation.

An increase or decrease in pressure can shift the equilibrium only in processes in which gaseous substances are involved, and which proceed with a change in volume.

To shift the equilibrium towards the initial substances with increasing pressure, it is necessary that the process proceeds with an increase in volume.

This is process 2. (Initial substances of 1 volume, reaction products - 2)

Answer: 2

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

Explanation.

If an increase in the concentration of hydrogen shifts the chemical equilibrium to the left, then it comes about hydrogen as a reaction product. The reaction product hydrogen is only in variant 3.

Answer: 3

In system

The shift of chemical equilibrium to the right is facilitated

1) increase in temperature

2) decrease in pressure

3) an increase in the concentration of chlorine

4) a decrease in the concentration of sulfur (IV) oxide

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 materials will contribute to

1) decrease in pressure

2) decrease in temperature

3) increased concentration

4) decrease in concentration

Explanation.

This reaction proceeds with a decrease in volume. With a decrease in pressure, the volume increases, therefore, the equilibrium shifts towards an increase in volume. In this reaction, towards the starting materials, i.e. to the left.

Answer: 1

Alexander Ivanov

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

Chemical equilibrium in the system

shifts to the right at

1) increasing pressure

2) lowering the temperature

3) increasing concentration

4) rise in 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 when the temperature rises, the equilibrium will shift to the right.

Answer: 4

On the state of chemical equilibrium in the system

1) increase in pressure

2) increased 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, with increasing pressure, the chemical equilibrium will shift towards the starting substances?

Explanation.

According to Le Chatelier's rule, with an increase in 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) increased concentration

3) increase in temperature

4) decrease in temperature

Explanation.

Changes in temperature and concentration of substances will affect the state of chemical equilibrium. At the same time, the amount of gaseous substances on the left and on the right is the same, therefore, even though the reaction takes place 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 at

1) increasing pressure

2) increasing concentration

3) lowering the temperature

4) rise in temperature

Explanation.

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

Answer: 4

In which system, the change in pressure has practically no effect on the shift in chemical equilibrium?

Explanation.

In the case of homogeneous reactions, a change in pressure practically does not affect the shift in chemical equilibrium in systems in which there is no change in the amount of mol of gaseous substances during the reaction. In this case, this is reaction number 3.

Answer: 3

In the system, the shift of chemical equilibrium towards the initial substances will be promoted by

1) decrease in pressure

2) decrease in temperature

3) decrease in concentration

4) increased concentration

Explanation.

Since this reaction is homogeneous and is accompanied by a decrease in the number of moles of gaseous substances, with a decrease in pressure, 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. With increasing pressure, the chemical equilibrium shifts towards the reaction product.

B. With a decrease in temperature, the chemical equilibrium in this system will shift towards the reaction product.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

Since this is a homogeneous reaction, accompanied by a decrease in the number of moles of gases, when the pressure increases, the chemical equilibrium shifts towards the reaction product. In addition, heat is released during the direct reaction, therefore, with a decrease in temperature, the chemical equilibrium in this system will shift towards the reaction product. Both are true.

Answer: 3

In system

a shift of chemical equilibrium to the right will occur when

1) increasing pressure

2) rise in temperature

3) an increase in the concentration of sulfur oxide (VI)

4) adding 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 proceeds, a decrease in pressure occurs, therefore an increase in pressure will cause a shift in 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 rises, the chemical equilibrium in this system will shift towards the starting materials.

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

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

Since heat is released in this system, then according to Le Chatelier's rule, with an increase in temperature, the chemical equilibrium in this system will indeed shift towards the initial substances. Since nitric oxide (II) is a reagent, with an increase in its concentration, the equilibrium will shift towards the products.

Answer: 1

Are the following judgments about the shift of chemical equilibrium in the system true?

A. With a decrease in temperature, the chemical equilibrium in this system will shift towards the reaction products.

B. With a decrease in the concentration of carbon monoxide, the equilibrium of the system will shift towards the reaction products.

1) only A is true

2) only B is true

3) both statements are true

4) both judgments are wrong

Explanation.

In this reaction, heat is released, therefore, with a decrease in temperature, the chemical equilibrium in this system will indeed shift towards the reaction products. Insofar as carbon monoxide- a reagent, then a decrease in its concentration will cause an equilibrium shift towards its formation - that is, towards the reagents.

Answer: 1

In system

a shift of chemical equilibrium to the right will occur when

1) increasing pressure

2) rise in temperature

3) an increase in the concentration of sulfur oxide (VI)

4) adding catalyst

Explanation.

In this homogeneous reaction, a decrease in the number of moles of gaseous substances occurs, therefore, a shift in chemical equilibrium to the right will occur with an increase in pressure.

Answer: 1

Chemical equilibrium in the system

shifts to the right at

1) increasing pressure

2) increasing concentration

3) lowering the temperature

4) rise in temperature

Explanation.

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

Answer: 4

With increasing pressure, the yield of the product (s) in the 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 (s) + 4H 2 O (g) Fe 3 O 4 (s) + 4H 2 (g)

Explanation.

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

Here it is necessary to find a reaction in which the equilibrium will shift to the left with increasing pressure. In this reaction, the number of moles of gaseous substances on the right should be greater than on the left. This is reaction number 3.

Answer: 3

shifts towards the reaction products at

1) lowering the temperature

2) lowering pressure

3) using a catalyst

4) rise in temperature

Explanation.

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

The equilibrium of the endothermic reaction shifts to the right with increasing temperature.

Answer: 4

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

Explanation.

A) 1) towards the reaction products

Answer: 1131

Match the equation chemical reaction and the direction of the displacement of the chemical equilibrium with increasing pressure in the system:

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

Explanation.

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

With increasing pressure, the equilibrium will shift towards a smaller amount of gaseous substances.

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 chemical reaction equation and the direction of displacement of chemical equilibrium with increasing pressure in the system:

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

Explanation.

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

With increasing pressure, the equilibrium will shift towards the reaction with a smaller amount of gaseous substances.

B) 2) towards the starting substances

B) 3) practically does not shift

D) 1) towards the reaction products

Answer: 2231

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

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

Explanation.

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

With increasing pressure, the equilibrium will shift towards the reaction with a smaller amount of gaseous substances.

A) 2) towards the starting substances

B) 1) towards the reaction products

B) 3) practically does not shift

D) 2) towards the starting substances

Answer: 2132

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

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

If external conditions chemical process do not change, then the state of chemical equilibrium can be maintained for an arbitrarily long time. By changing the reaction conditions (temperature, pressure, concentration), you can achieve displacement or shift of chemical equilibrium in the required direction.

A shift in equilibrium to the right leads to an increase in the concentration of substances, the formulas of which are on the right side of the equation. A shift in equilibrium to the left will lead to an increase in the concentration of substances whose formulas are on the left. In this case, the system will enter a new equilibrium state characterized by other values ​​of the equilibrium concentrations of the reaction participants.

The shift in chemical equilibrium caused by a change in conditions obeys a rule formulated in 1884 by the French physicist A. Le Chatelier (Le Chatelier's principle).

Le Chatelier's principle:if an effect is exerted on a system in a state of chemical equilibrium, for example, to change the temperature, pressure or concentration of reagents, then the equilibrium will shift in the direction of the reaction that weakens the effect .

The effect of changes in concentration on the shift in chemical equilibrium.

According to the Le Chatelier principle an increase in the concentration of any of the participants in the reaction causes a shift in equilibrium towards the reaction that leads to a decrease in the concentration of this substance.

The effect of concentration on equilibrium is governed by the following rules:

With an increase in the concentration of one of the initial substances, the rate of the direct reaction increases and the equilibrium shifts in the direction of the formation of the reaction products and vice versa;

With an increase in the concentration of one of the reaction products, the rate of the reverse reaction increases, which leads to a shift in equilibrium in the direction of the formation of the initial substances and vice versa.

For example, if in an equilibrium system:

SO 2 (g) + NO 2 (g) SO 3 (g) + NO (g)

increase the concentration of SO 2 or NO 2, then, in accordance with the law of mass action, the rate of the direct reaction will increase. This will lead to a shift in the equilibrium to the right, which will lead to the consumption of the starting materials and an increase in the concentration of the reaction products. A new state of equilibrium will be established with new equilibrium concentrations of the initial substances and reaction products. When the concentration of, for example, one of the reaction products decreases, the system will react in such a way as to increase the concentration of the product. The direct reaction will be advantageous, leading to an increase in the concentration of the reaction products.

The effect of pressure changes on the shift in chemical equilibrium.

According to the Le Chatelier principle an increase in pressure leads to a shift in equilibrium towards the formation of a smaller amount of gaseous particles, i.e. towards a smaller volume.

For example, in a reversible reaction:

2NO 2 (g) 2NO (g) + O 2 (g)

from 2 mol of NO 2, 2 mol of NO and 1 mol of O 2 are formed. The stoichiometric coefficients in front of the formulas of gaseous substances indicate that the course of the direct reaction leads to an increase in the number of moles of gases, and the course of the reverse reaction, on the contrary, decreases the number of moles of the gaseous substance. If an external influence is exerted on such a system by, for example, by increasing the pressure, then the system will react in such a way as to weaken this influence. The pressure can decrease if the equilibrium of this reaction shifts towards a smaller number of moles of a gaseous substance, and therefore a smaller volume.

On the contrary, an increase in pressure in this system is associated with a shift of equilibrium to the right - towards the decomposition of NO 2, which increases the amount of gaseous matter.

If the number of moles of gaseous substances before and after the reaction remains constant, i.e. the volume of the system does not change in the course of the reaction, then a change in pressure equally changes the rates of forward and reverse reactions and does not affect the state of chemical equilibrium.

For example, in a reaction:

H 2 (g) + Cl 2 (g) 2HCl (g),

the total number of moles of gaseous substances before and after the reaction remains constant and the pressure in the system does not change. The equilibrium in this system does not shift when the pressure changes.

The effect of temperature change on the shift in chemical equilibrium.

In each reversible reaction, one of the directions corresponds to an exothermic process, and the other to an endothermic one. So in the reaction of ammonia synthesis, the direct reaction is exothermic, and the reverse reaction is endothermic.

N 2 (g) + 3H 2 (g) 2NH 3 (g) + Q (-ΔH).

When the temperature changes, the rates of both direct and reverse reactions change, however, the rate change does not occur to the same extent. According to the Arrhenius equation in to a greater extent an endothermic reaction, characterized by great value activation energy.

Consequently, to assess the effect of temperature on the direction of the displacement of chemical equilibrium, it is necessary to know the thermal effect of the process. It can be determined experimentally, for example, using a calorimeter, or calculated on the basis of Hess's law. It should be noted that a change in temperature leads to a change in the value of the constant of chemical equilibrium (K p).

According to the Le Chatelier principle an increase in temperature shifts the equilibrium towards an endothermic reaction. As the temperature decreases, the equilibrium shifts in the direction of the exothermic reaction.

Thus, temperature increase in the ammonia synthesis reaction will lead to a shift in equilibrium towards endothermic reactions, i.e. to the left. The reverse reaction with heat absorption gains the advantage.

Chemical reactions are reversible and irreversible.

those. if some reaction A + B = C + D is irreversible, it means that the reverse reaction C + D = A + B does not occur.

i.e., for example, if a certain reaction A + B = C + D is reversible, this means that both the reaction A + B → C + D (direct) and the reaction C + D → A + B (reverse ).

In fact, since both direct and reverse reactions take place; in the case of reversible reactions, both the substances on the left side of the equation and the substances on the right side of the equation can be called reagents (starting materials). The same goes for products.

For any reversible reaction, a situation is possible when the rates of the forward and reverse reactions are equal. This state is called state of equilibrium.

In a state of equilibrium, the concentrations of both all reagents and all products are unchanged. The concentrations of products and reagents in equilibrium are called equilibrium concentrations.

Displacement of chemical equilibrium under the influence of various factors

Due to such external influences on the system as changes in temperature, pressure or concentration of starting substances or products, the equilibrium of the system can be disturbed. However, after the termination of this external influence, the system, after some time, will pass into a new state of equilibrium. Such a transition of the system from one equilibrium state to another equilibrium state is called shift (shift) of chemical equilibrium .

In order to be able to determine how the chemical equilibrium shifts under a particular type of action, it is convenient to use Le Chatelier's principle:

If an external influence is exerted on the system in a state of equilibrium, then the direction of the displacement of the chemical equilibrium will coincide with the direction of the reaction that weakens the effect of the influence exerted.

Effect of temperature on equilibrium

As the temperature changes, the equilibrium of any chemical reaction shifts. This is due to the fact that any reaction has a thermal effect. In this case, the thermal effects of direct and reverse reactions are always directly opposite. Those. if the direct reaction is exothermic and proceeds with a thermal effect equal to + Q, then the reverse reaction is always endothermic and has a thermal effect equal to –Q.

Thus, in accordance with Le Chatelier's principle, if we increase the temperature of some system in equilibrium, then the equilibrium will shift towards the reaction, during which the temperature decreases, i.e. towards the endothermic reaction. And similarly, if we lower the temperature of the system in a state of equilibrium, the equilibrium will shift towards the reaction, as a result of which the temperature will rise, i.e. towards an exothermic reaction.

For example, consider the following reversible reaction and indicate where its equilibrium will shift with decreasing temperature:

As you can see from the equation above, the direct reaction is exothermic, i.e. as a result of its flow, heat is released. Consequently, the reverse reaction will be endothermic, that is, it takes place with heat absorption. By condition, the temperature is lowered; therefore, the equilibrium will shift to the right, i.e. towards a direct reaction.

Effect of concentration on chemical equilibrium

An increase in the concentration of reagents in accordance with Le Chatelier's principle should lead to a shift in the equilibrium towards the reaction as a result of which the reagents are consumed, i.e. towards a direct reaction.

Conversely, if the concentration of the reagents is lowered, then the equilibrium will shift towards the reaction, as a result of which the reagents are formed, i.e. side of the reverse reaction (←).

The change in the concentration of the reaction products has a similar effect. If the concentration of the products is increased, the equilibrium will shift towards the reaction, as a result of which the products are consumed, i.e. towards the reverse reaction (←). If, on the contrary, the concentration of products is lowered, then the equilibrium will shift towards the direct reaction (→), in order for the concentration of products to increase.

Effect of pressure on chemical equilibrium

Unlike temperature and concentration, changes in pressure do not affect the equilibrium state of every reaction. In order for a change in pressure to lead to a shift in chemical equilibrium, the sums of the coefficients in front of gaseous substances on the left and right sides of the equation must be different.

Those. of two reactions:

a change in pressure can affect the state of equilibrium only in the case of a second reaction. Since the sum of the coefficients in front of the formulas of gaseous substances in the case of the first equation on the left and on the right is the same (equal to 2), and in the case of the second equation, it is different (4 on the left and 2 on the right).

From this, in particular, it follows that if there are no gaseous substances among both the reagents and the products, then the change in pressure will in no way affect Current state balance. For example, pressure will have no effect on the equilibrium state of the reaction:

If, on the left and right, the amount of gaseous substances is different, then an increase in pressure will lead to a shift in equilibrium towards the reaction, during which the volume of gases decreases, and a decrease in pressure will lead to the direction of the reaction, as a result of which the volume of gases increases.

Effect of a catalyst on chemical equilibrium

Since the catalyst equally accelerates both forward and reverse reactions, its presence or absence does not affect in any way to a state of equilibrium.

The only thing that a catalyst can affect is the rate of transition of the system from a nonequilibrium state to an equilibrium one.

The impact of all of the above factors on chemical equilibrium is summarized below in a cheat sheet, which you can first peep into when performing equilibrium tasks. However, she will not be able to use it on the exam, therefore, after analyzing several examples with her help, she should be learned and trained to solve balance tasks, no longer peeping into her:

Legend: T - temperature, p - pressure, with - concentration, - increase, ↓ - decrease