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When the conditions of the chemical equilibrium system change, the equilibrium state may be destroyed and the system changes from equilibrium to imbalance
.
Under changed conditions, the reversible reaction will proceed in a certain direction until a new equilibrium state is reached
According to Le Chatelier's principle, if an external force is applied to the balance system, the balance will move in a direction that reduces its influence
.
4.
3.
1 The effect of concentration on balance
Reaction in solution
If [A], [B], [G], [H] are the equilibrium concentrations of each substance, the standard equilibrium constant of the reaction is
Obviously, when the concentration of reactants is increased in the equilibrium system, the value of the reaction relative quotient Q Θ decreases due to the increase of its denominator, so Q Θ <K Θ , the reaction proceeds in the positive reaction direction, that is, the equilibrium is in the positive reaction direction Move
.
In the same way, increase the concentration of the product, and the balance moves in the direction of the reverse reaction
4.
3.
2 The influence of pressure on balance
Gas phase reaction
If pA, pB, pG, pH are used to represent the equilibrium partial pressure of each substance, the standard equilibrium constant is
Assuming that the total pressure of the reaction system increases by n times (n>1), the instantaneous partial pressure of each substance is npA, npB, npG, and npH
.
Then, the relative quotient of the response at this time is
Put the value of n, get
Organize, get
Q Θ =K Θ ×n (g+h)-(a+b)
which is
Q Θ =K Θ ×n △v
When △v=0, Q Θ =K
.
In other words, for a chemical reaction in which gas participates and the stoichiometric number of gaseous substances does not change before and after the reaction, changes in pressure have no effect on the balance
When △v≠0, Q Θ ≠K Θ , the balance will move
.
(1) If Δv>0 (the stoichiometric number of gaseous molecules in the reaction system increases), then Q Θ >K Θ
.
Increasing the pressure (n>1) balance will move to the opposite reaction direction, that is, move to the direction where the number of gaseous molecules decreases
(2) If △v<0 (the stoichiometric number of gaseous molecules in the reaction system decreases), then Q Θ <K Θ , increasing the pressure (n>1) will move the balance in the direction of the positive reaction, that is, toward the increase in the number of gaseous molecules Move in the direction
.
Therefore, for chemical reactions involving gaseous substances, when the pressure of the system increases, the equilibrium moves in the direction of decreasing the number of gaseous molecules; when the pressure of the system decreases, the equilibrium moves in the direction of increasing the number of gaseous molecules
.
[Example 4-5] At a certain temperature, the decomposition reaction of N 2 O 4 is
N at a total pressure of 100 kPa 2 O .
4 Solutions of from 20%, at a total pressure of N seek time of 200 kPa 2 O .
4 Solution of ex
Set the initial amount of N 2 O 4 as 1 mol, and the equilibrium dissociation degree as a
If the temperature does not change, when p total = 200 kPa
Substituting into the above formula, we get
a=0.
14
The degree of dissociation of N 2 O 4 decreased, indicating that the pressure increased and the equilibrium moved in the direction of decreasing the number of gas molecules
.
The change in volume also has an impact on the chemical balance.
The change in volume is usually attributed to a change in concentration or pressure, that is, an increase in volume is equivalent to a decrease in concentration or pressure, and a decrease in volume is equivalent to an increase in concentration or pressure