If a system is in a state of equilibrium, then it will remain in it as long as external conditions remain constant. If the conditions change, the system will go out of equilibrium - the rates of the forward and reverse processes will change unequally - a reaction will occur. Highest value there are cases of imbalance due to changes in the concentration of any of the substances involved in the equilibrium, pressure or temperature.
Let's consider each of these cases.
Disturbance of equilibrium due to a change in the concentration of any of the substances participating in the reaction. Let hydrogen, hydrogen iodide and iodine vapor be in equilibrium with each other at a certain temperature and pressure. Let us introduce an additional amount of hydrogen into the system. According to the law of mass action, an increase in the concentration of hydrogen will entail an increase in the rate of the forward reaction - the HI synthesis reaction, while the rate of the reverse reaction will not change. The reaction will now proceed faster in the forward direction than in the reverse direction. As a result of this, the concentrations of hydrogen and iodine vapor will decrease, which will slow down the forward reaction, and the concentration of HI will increase, which will accelerate the reverse reaction. After some time, the rates of the forward and reverse reactions will become equal again, and a new equilibrium will be established. But at the same time, the concentration of HI will now be higher than it was before adding , and the concentration will be lower.
The process of changing concentrations caused by an imbalance is called a displacement or equilibrium shift. If at the same time there is an increase in the concentrations of substances on the right side of the equation (and, of course, at the same time a decrease in the concentrations of substances on the left), then they say that the equilibrium shifts to the right, i.e., in the direction of the direct reaction; when the concentrations change in the opposite direction, they speak of a shift in equilibrium to the left - in the direction of the reverse reaction. In the example considered, the equilibrium has shifted to the right. At the same time, the substance, the increase in concentration of which caused an imbalance, entered into a reaction - its concentration decreased.
Thus, with an increase in the concentration of any of the substances participating in the equilibrium, the equilibrium shifts towards the consumption of this substance; When the concentration of any substance decreases, the equilibrium shifts towards the formation of this substance.
Disturbance of equilibrium due to changes in pressure (by decreasing or increasing the volume of the system). When gases are involved in a reaction, equilibrium may be disrupted when the volume of the system changes.
Consider the effect of pressure on the reaction between nitrogen monoxide and oxygen:
Let a mixture of gases be in chemical equilibrium at a certain temperature and pressure. Without changing the temperature, we increase the pressure so that the volume of the system decreases by 2 times. At the first moment, the partial pressures and concentrations of all gases will double, but at the same time the ratio between the rates of forward and reverse reactions will change - the equilibrium will be disrupted.
In fact, before the pressure increased, the gas concentrations had equilibrium values , and , and the rates of the forward and reverse reactions were the same and were determined by the equations:
At the first moment after compression, the gas concentrations will double compared to their initial values and will be equal to , and , respectively. In this case, the rates of forward and reverse reactions will be determined by the equations:
Thus, as a result of increasing pressure, the rate of the forward reaction increased 8 times, and the reverse reaction only 4 times. The equilibrium in the system will be disrupted - the forward reaction will prevail over the reverse one. After the speeds become equal, equilibrium will be established again, but the quantity in the system will increase, and the equilibrium will shift to the right.
It is easy to see that the unequal change in the rates of forward and reverse reactions is due to the fact that on the left and right sides of the equation of the reaction under consideration the number of gas molecules is different: one molecule of oxygen and two molecules of nitrogen monoxide (three gas molecules in total) are converted into two gas molecules - nitrogen dioxide. The pressure of a gas is the result of its molecules hitting the walls of the container; other things being equal, the higher the number of molecules contained in a given volume of gas, the higher the gas pressure. Therefore, a reaction that occurs with an increase in the number of gas molecules leads to an increase in pressure, and a reaction that occurs with a decrease in the number of gas molecules leads to a decrease in pressure.
With this in mind, the conclusion about the effect of pressure on chemical equilibrium can be formulated as follows:
When the pressure increases by compressing the system, the equilibrium shifts towards a decrease in the number of gas molecules, i.e. towards a decrease in pressure; when the pressure decreases, the equilibrium shifts towards an increase in the number of gas molecules, i.e. towards an increase in pressure.
In the case when the reaction proceeds without changing the number of gas molecules, the equilibrium is not disturbed during compression or expansion of the system. For example, in the system
equilibrium is not disturbed when volume changes; the HI output is independent of pressure.
Disequilibrium due to temperature changes. The equilibrium of the vast majority of chemical reactions shifts with temperature changes. The factor that determines the direction of the equilibrium shift is the sign of the thermal effect of the reaction. It can be shown that when the temperature increases, the equilibrium shifts in the direction of the endothermic reaction, and when it decreases, in the direction of the exothermic reaction.
Thus, ammonia synthesis is an exothermic reaction
Therefore, as the temperature increases, the equilibrium in the system shifts to the left - towards the decomposition of ammonia, since this process occurs with the absorption of heat.
Conversely, the synthesis of nitric oxide (II) is an endothermic reaction:
Therefore, as the temperature increases, the equilibrium in the system shifts to the right - towards the formation.
The patterns that appear in the considered examples of chemical imbalance are special cases general principle, which determines the influence various factors to equilibrium systems. This principle, known as Le Chatelier's principle, when applied to chemical equilibria, can be formulated as follows:
If any impact is exerted on a system that is in equilibrium, then as a result of the processes occurring in it, the equilibrium will shift in such a direction that the impact will decrease.
Indeed, when one of the substances participating in the reaction is introduced into the system, the equilibrium shifts towards the consumption of this substance. “When the pressure increases, it shifts so that the pressure in the system decreases; when the temperature increases, the equilibrium shifts towards the endothermic reaction - the temperature in the system drops.
Le Chatelier's principle applies not only to chemical, but also to various physicochemical equilibria. A shift in equilibrium when the conditions of processes such as boiling, crystallization, and dissolution change occurs in accordance with Le Chatelier’s principle.
If the external conditions of a chemical process do not change, then the state of chemical equilibrium can remain indefinitely. By changing the reaction conditions (temperature, pressure, concentration) you can achieve displacement or shift in chemical equilibrium in the required direction.
A shift of equilibrium to the right leads to an increase in the concentration of substances whose formulas 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 move to a new state of equilibrium, characterized by other values of equilibrium concentrations of reaction participants.
The shift in chemical equilibrium caused by changing conditions obeys the rule formulated in 1884 by the French physicist A. Le Chatelier (Le Chatelier's principle).
Le Chatelier's Principle:if a system in a state of chemical equilibrium is subject to any influence, for example, by changing temperature, pressure or concentrations 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 Le Chatelier's principle An increase in the concentration of any of the reaction participants causes a shift in equilibrium towards the reaction that leads to a decrease in the concentration of this substance.
The influence of concentration on the state of equilibrium is subject to the following rules:
As the concentration of one of the starting substances increases, the rate of the forward reaction increases and the equilibrium shifts towards the formation of reaction products and vice versa;
As the concentration of one of the reaction products increases, the rate of the reverse reaction increases, which leads to a shift in the equilibrium in the direction of the formation of the starting 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 of equilibrium to the right, which will lead to the consumption of starting substances and an increase in the concentration of reaction products. A new equilibrium state will be established with new equilibrium concentrations of the starting 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 advantage will be given to the direct reaction, leading to an increase in the concentration of reaction products.
The influence of pressure changes on the shift of chemical equilibrium.
According to Le Chatelier's principle an increase in pressure leads to a shift in equilibrium towards the formation of fewer gaseous particles, i.e. towards smaller volume.
For example, in a reversible reaction:
2NO 2 (g) 2NO (g) + O 2 (g)
from 2 mol NO 2 2 mol NO and 1 mol O 2 are formed. Stoichiometric coefficients in front of the formulas of gaseous substances indicate that the occurrence of a forward reaction leads to an increase in the number of moles of gases, and the occurrence of a reverse reaction, on the contrary, reduces the number of moles of a gaseous substance. If an external influence is exerted on such a system by, for example, increasing pressure, then the system will react in such a way as to weaken this influence. The pressure can decrease if the equilibrium of a given reaction shifts toward fewer moles of the gaseous substance, and therefore a smaller volume.
On the contrary, an increase in pressure in this system is associated with a shift in 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 during 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 react:
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 pressure changes.
The influence of temperature changes on the shift of chemical equilibrium.
In each reversible reaction, one of the directions corresponds to an exothermic process, and the other to an endothermic process. So in the reaction of ammonia synthesis, the forward 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 forward and reverse reactions change, however, the rate changes do not occur to the same extent. According to the Arrhenius equation in to a greater extent An endothermic reaction, characterized by great value activation energies.
Therefore, to assess the influence of temperature on the direction of shift 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 based on G. Hess's law. It should be noted that a change in temperature leads to a change in the value of the chemical equilibrium constant (K p).
According to Le Chatelier's principle An increase in temperature shifts the equilibrium towards an endothermic reaction. As the temperature decreases, the equilibrium shifts towards 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 advantage is given to the reverse reaction, which occurs with the absorption of heat.
Chemical equilibrium in the reaction is shifted towards the formation of the reaction product at
1) decrease in pressure
2) increasing temperature
3) adding a catalyst
4) adding hydrogen
Explanation.
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 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.
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 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 that is 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. As the concentration of carbon dioxide increases, 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.
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 reagents. Statement A is incorrect.
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 increase
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.
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.
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 of an ester will contribute to
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, with increasing pressure, 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 are talking 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) pressure reduction
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) pressure reduction
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 affect1) 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, with increasing pressure, 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) pressure reduction
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. As pressure increases, the chemical equilibrium shifts toward 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 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.
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.
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.
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
Match the equation chemical reaction and the direction of the shift in 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.
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.
As pressure increases, the equilibrium will shift toward 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.
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.
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.
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.
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 reactions can be reversible or irreversible.
those. if some reaction A + B = C + D is irreversible, this 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) occur simultaneously ).
Essentially, because both direct and reverse reactions occur with reagents (starting substances) in the case reversible reactions Both the substances on the left side of the equation and the substances on the right side of the equation can be named. 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 condition is called state of balance.
At equilibrium, the concentrations of both all reactants and all products are constant. The concentrations of products and reactants at equilibrium are called equilibrium concentrations.
Shift in chemical equilibrium under the influence of various factors
Due to external influences on the system, such as changes in temperature, pressure or concentration of starting substances or products, the equilibrium of the system may be disrupted. However, after the cessation of this external influence, the system will, after some time, move to a new state of equilibrium. Such a transition of a system from one equilibrium state to another equilibrium state is called displacement (shift) of chemical equilibrium .
In order to be able to determine how the chemical equilibrium shifts under a particular type of influence, it is convenient to use Le Chatelier’s principle:
If any external influence is exerted on a system in a state of equilibrium, then the direction of the shift in chemical equilibrium will coincide with the direction of the reaction that weakens the effect of the influence.
The influence of temperature on the state of equilibrium
When temperature changes, the equilibrium of any chemical reaction shifts. This is due to the fact that any reaction has a thermal effect. Moreover, the thermal effects of the forward and reverse reactions are always directly opposite. Those. if the forward 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 a certain system that is in a state of equilibrium, then the equilibrium will shift towards the reaction during which the temperature decreases, i.e. towards an 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 increase, i.e. towards an exothermic reaction.
For example, consider the following reversible reaction and indicate where its equilibrium will shift as the temperature decreases:
As can be seen from the equation above, the forward reaction is exothermic, i.e. As a result of its occurrence, heat is released. Consequently, the reverse reaction will be endothermic, that is, it occurs with the absorption of heat. According to the condition, the temperature is reduced, therefore, the equilibrium will shift to the right, i.e. towards 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 equilibrium towards the reaction as a result of which the reagents are consumed, i.e. towards direct reaction.
And vice versa, if the concentration of the reactants is reduced, then the equilibrium will shift towards the reaction as a result of which the reactants are formed, i.e. side of the reverse reaction (←).
A change in the concentration of reaction products has a similar effect. If the concentration of 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 reduced, then the equilibrium will shift towards the direct reaction (→), so that the concentration of products increases.
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 for 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 equilibrium state only in the case of the 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 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 here, in particular, it follows that if there are no gaseous substances among both the reactants and products, then a change in pressure will not in any way affect the current state of equilibrium. For example, pressure will not affect the equilibrium state of the reaction:
If, on the left and right, the amount of gaseous substances differs, 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 a shift in the equilibrium, as a result of which the volume of gases increases.
Effect of a catalyst on chemical equilibrium
Since a catalyst equally accelerates both forward and reverse reactions, its presence or absence has no effect to a state of equilibrium.
The only thing a catalyst can affect is the rate of transition of the system from a nonequilibrium state to an equilibrium one.
The impact of all the above factors on chemical equilibrium is summarized below in a cheat sheet, which you can initially look at when performing equilibrium tasks. However, it will not be possible to use it in the exam, so after analyzing several examples with its help, you should learn it and practice solving equilibrium problems without looking at it:
Designations: T - temperature, p - pressure, With – concentration, – increase, ↓ – decrease
|
T |
T - equilibrium shifts towards the endothermic reaction |
| ↓T - equilibrium shifts towards the exothermic reaction | |
|
p |
p - equilibrium shifts towards the reaction with a smaller sum of coefficients in front of gaseous substances |
| ↓p - the equilibrium shifts towards the reaction with a larger amount coefficients for gaseous substances | |
|
c |
c (reagent) – the equilibrium shifts towards the direct reaction (to the right) |
| ↓c (reagent) – the equilibrium shifts towards the reverse reaction (to the left) | |
| c (product) – equilibrium shifts towards the reverse reaction (to the left) | |
| ↓c (product) – the equilibrium shifts towards the direct reaction (to the right) | |
| Doesn't affect balance!!! |
Studying the parameters of a system including starting materials and reaction products, makes it possible to find out which factors shift the chemical equilibrium and lead to the desired changes. Industrial technologies are based on the conclusions of Le Chatelier, Brown and other scientists about methods of carrying out reversible reactions, which make it possible to carry out processes that previously seemed impossible and obtain economic benefits.
Variety of chemical processes
Based on the characteristics of the thermal effect, many reactions are classified as exo- or endothermic. The first come with the formation of heat, for example, the oxidation of carbon, the hydration of concentrated sulfuric acid. The second type of change is associated with the absorption of thermal energy. Examples of endothermic reactions: decomposition of calcium carbonate with the formation of slaked lime and carbon dioxide, formation of hydrogen and carbon during the thermal decomposition of methane. In the equations of exo- and endothermic processes, it is necessary to indicate the thermal effect. The redistribution of electrons between the atoms of the reacting substances occurs in redox reactions. Four types of chemical processes are distinguished according to the characteristics of the reagents and products:
To characterize the processes, the completeness of the interaction of the reacting compounds is important. This feature underlies the division of reactions into reversible and irreversible.
Reversibility of reactions
Reversible processes make up the majority of chemical phenomena. The formation of final products from reactants is a direct reaction. In the reverse, the starting substances are obtained from the products of their decomposition or synthesis. In the reacting mixture, a chemical equilibrium arises in which the same number of compounds is obtained as the original molecules decompose. In reversible processes, instead of the “=” sign between reactants and products, the symbols “↔” or “⇌” are used. The arrows may be unequal in length, which is due to the dominance of one of the reactions. In chemical equations, you can indicate the aggregate characteristics of substances (g - gases, g - liquids, t - solids). Huge practical significance have scientifically proven methods of influencing reversible processes. Thus, the production of ammonia became profitable after creating conditions that shifted the equilibrium towards the formation of the target product: 3H 2 (g) + N 2 (g) ⇌ 2NH 3 (g). Irreversible phenomena lead to the appearance of an insoluble or slightly soluble compound and the formation of a gas that leaves the reaction sphere. Such processes include ion exchange and the breakdown of substances.
Chemical equilibrium and conditions for its displacement
The characteristics of the forward and reverse processes are influenced by several factors. One of them is time. The concentration of the substance taken for the reaction gradually decreases, and the final compound increases. The forward reaction is slower and slower, and the reverse process is gaining speed. At a certain interval, two opposing processes occur synchronously. Interactions between substances occur, but concentrations do not change. The reason is the dynamic chemical equilibrium established in the system. Its preservation or change depends on:
- temperature conditions;
- concentrations of compounds;
- pressure (for gases).
Chemical equilibrium shift
In 1884, the outstanding scientist from France A.L. Le Chatelier proposed a description of ways to remove a system from the state dynamic equilibrium. The method is based on the principle of leveling the action external factors. Le Chatelier noticed that processes arise in the reacting mixture that compensate for the influence of extraneous forces. The principle formulated by the French researcher states that a change in conditions in a state of equilibrium favors the occurrence of a reaction that weakens external influences. The equilibrium shift obeys this rule; it is observed when the composition, temperature conditions and pressure change. Technologies based on the findings of scientists are used in industry. Many chemical processes, considered practically impracticable, are carried out thanks to methods of shifting the equilibrium.
Effect of concentration
A shift in equilibrium occurs if certain components are removed from the interaction zone or additional portions of a substance are introduced. Removing products from the reaction mixture usually causes an increase in the rate of their formation; adding substances, on the contrary, leads to their preferential decomposition. In the esterification process, sulfuric acid is used for dehydration. When it is introduced into the reaction sphere, the yield of methyl acetate increases: CH 3 COOH + CH 3 OH ↔ CH 3 COOCH 3 + H 2 O. If you add oxygen that interacts with sulfur dioxide, the chemical equilibrium shifts towards the direct reaction of the formation of sulfur trioxide. Oxygen binds into SO 3 molecules, its concentration decreases, which is consistent with Le Chatelier's rule for reversible processes.
Temperature change
Processes that involve the absorption or release of heat are endothermic and exothermic. To shift the equilibrium, heating or heat removal from the reacting mixture is used. An increase in temperature is accompanied by an increase in the rate of endothermic phenomena, in which additional energy is absorbed. Cooling leads to the advantage of exothermic processes that occur with the release of heat. When carbon dioxide interacts with coal, heating is accompanied by an increase in the concentration of monoxide, and cooling leads to the predominant formation of soot: CO 2 (g) + C (t) ↔ 2CO (g).
Effect of pressure
Pressure change - important factor for reacting mixtures including gaseous compounds. You should also pay attention to the difference in volumes of the original and resulting substances. A decrease in pressure leads to a preferential occurrence of phenomena in which the total volume of all components increases. An increase in pressure directs the process towards a decrease in the volume of the entire system. This pattern is observed in the reaction of ammonia formation: 0.5N 2 (g) + 1.5 N 2 (g) ⇌ NH 3 (g). A change in pressure will not affect the chemical equilibrium in those reactions that occur at a constant volume.
Optimal conditions for the chemical process
Creating conditions for a shift in equilibrium largely determines the development of modern chemical technologies. Practical use scientific theory contributes to optimal production results. Most shining example- obtaining ammonia: 0.5N 2 (g) + 1.5 N 2 (g) ⇌ NH 3 (g). An increase in the content of N 2 and H 2 molecules in the system is favorable for the synthesis of complex substances from simple ones. The reaction is accompanied by the release of heat, so a decrease in temperature will cause an increase in the concentration of NH 3. Volume original components more than the target product. An increase in pressure will ensure an increase in the yield of NH 3.
Under production conditions, the optimal ratio of all parameters (temperature, concentration, pressure) is selected. In addition, it has great importance area of contact between reagents. In solid heterogeneous systems, an increase in surface area leads to an increase in the reaction rate. Catalysts increase the rate of forward and reverse reactions. The use of substances with such properties does not lead to a shift in chemical equilibrium, but accelerates its onset.