Reversible reaction, also called confrontation reaction, refers to the reaction that can be carried out in the direction of both positive reaction and reverse reaction under the same conditions.Most reactions are reversible. Some reactions are not reversible under general conditions, and changing conditions (such as placing reactants in a closed environment, high temperature reaction, etc.) will become reversible.
Chinese name
Reversible reaction
Foreign name
reversible reaction
Discipline
Chemistry
influence factor
Pressure, temperature, concentration, etc
Alias
Confrontation reaction
Features
Most reactions are reversible
Definition
Under the same conditions, the reaction can be carried out in both the positive reaction direction and the reverse reaction direction
Confrontal reaction, also called reversible reaction, refers to the reaction that can be carried out in the direction of both positive reaction and reverse reaction under the same conditions.Most reactions are reversible. Some reactions are not reversible under general conditions, and changing conditions (such as placing reactants in a closed environment, high temperature reaction, etc.) will become reversible.
characteristic
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1. The reaction cannot be carried out to the end.No matter how long the reversible reaction lasts, the reactants cannot be 100% converted into products.
2. The reversible reaction must be a reaction that can convert each other under the same conditions, for example, sulfur dioxide and oxygen generate sulfur trioxide under the conditions of catalyst and heating;Under the same conditions, sulfur trioxide can be decomposed into sulfur dioxide and oxygen.
3. In an ideal reversible process, there is no friction, resistance, hysteresis and other resistance, so there is no loss of active power.
4. A reaction that occurs at the same time.
5. The same increase and decrease.
6. When writing the chemical equation of reversible reaction, use the double arrows to indicate that the substances on both sides of the arrows are reactants and products of each other.Usually, the reaction from left to right is called positive reaction, and the reaction from right to left is called reverse reaction.
7. Two chemical reactions in a reversible reaction are simultaneously conducted in opposite directions under the same conditions, and the two chemical reactions form an opposing unity.Two chemical reactions that can go in opposite directions under different conditions cannot be called reversible reactions.
Balanced judgment
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(1) Ratevjust=vinverse（vNot 0)
(2) The percentage content of each substance remained unchanged;The concentration of each substance does not change with time;The amount of each substance does not change with time.
(3) In case of reaction with gas, the total pressure of mixed gas or the amount of total substance or the average density of gas does not change with time.(When gas metering at both ends of reactioncoefficientWhen the sum is unequal)
(4) In the case of a gas reaction, the average mass of the gas mixture remains unchanged.
(5) For the reversible reaction involving colored substances, if the color of the system remains unchanged, the reaction will reach an equilibrium state.
(6) Since any chemical reaction is accompanied by the change of energy, under other conditions, when the temperature of the total system is fixed, the reaction will reach equilibrium.
Judgment of balance moving direction
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(1) The root cause of balanced movement isvjust≠vinverse
vjust>vinverse: The balance moves towards the positive reaction direction.
vjust<vinverse: The balance moves in the direction of negative reaction.
(2) The balance movement direction can be judged according to Le Chatelier principle
If you change a condition that affects the balance (such as concentration, temperature, pressure, etc.), the balance will move in the direction that can weaken this change.
(3) Judgment of some special cases
1. Reversible reaction with constant volume before and after reaction, volume decreases or increases, and equilibrium does not move
2. Inert gas filling (refers to the substance that does not react with the substance in the system)
a、Inert gas is filled at constant temperature and volume. Although the total pressure of the system increases, the concentration of each component of the original equilibrium mixture does not change, and the equilibrium does not move
b、When inert gas is filled at constant temperature and pressure, the volume increases, and the concentration of each component of the equilibrium mixture decreases, which is equivalent to reducing the pressure, and the equilibrium moves to the direction of volume increase
Identical balance
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Content: For a reversible reaction, under certain conditions, the same equilibrium state can be established whether the reaction starts from the positive reaction or the reverse reaction, that is, the same equilibrium state can be reached under different starting conditions.There are two kinds of equilibrium states here:
(1) When the temperature and volume are fixed, the amount of each substance is the same in equilibrium.At this time, the different initial states are actually equivalent to one initial state.
The judgment method is to completely classify the products into reactants or products according to the equation. If the quantity is the same, it is the same equilibrium state. If the quantity is different, it is not the same equilibrium state.
(2) When the temperature and pressure are fixed (that is, the volume is variable), the concentration or percentage content of each substance is the same in equilibrium.At this time, the different initial states will reach the same equilibrium state as long as the ratio of reactants is the same after the products are returned to zero.
(3) For reactions with the same volume of gas before and after the reaction.In addition to meeting the above conditions, it is also possible to have the same percentage content of each substance in equilibrium but different concentrations under constant temperature and constant volume conditions.At this time, the different initial states will reach the same equilibrium state as long as the ratio of reactants is the same after the products are returned to zero.
