Effect of Change in Concentration (Le Chatelier’s Principle)

For the reaction, (ce{A<=>B} )

Addition or removal of reactants or products from a reaction equilibrium disturbs the equilibrium conditions and triggers a forward or backward reaction. The forward or backward reaction takes place as per the Le chatelier’s Principle.

Change in Concentration of Reactants

If additional amount of reactant (A) is added to the reaction equilibrium, the reaction moves in such a way to counter the increase in reactant amount . This happens if the reaction takes place in forward reaction that consumes the reactant. Similarly, if some amount of reactant (A) is taken out of the equilibrium, the system tries to generate the reactant. And, this can happen only if the net reaction is in backward direction.

Mathematically (at equilibrium),

(Q_c = {[B] over [A] }) = (K_c)

If ([A]) increases, the denominator of (Q_c) increases bringing down the value of (Q_c). This makes (Q_c < K_c). Hence, net reaction moves in forward direction.

Similarly, if ([A]) decreases, the denominator of (Q_c) decreases bringing up the value of (Q_c). This makes (Q_c > K_c). Hence, net reaction moves in backward direction.

Change in Concentration of Products

If additional amount of product (B) is added to the reaction equilibrium, the reaction moves in such a way to counter the increase in product. This happens if the reaction takes place in backward reaction that consumes the product. Similarly, if some amount of product(B) is taken out of the equilibrium, the system tries to generate the product. And, this can happen only if the net reaction is in forward direction.

(Q_c = {[B] over [A] }) = (K_c)

If ([B]) increases, the numerator of (Q_c) increases bringing up the value of (Q_c). This makes (Q_c > K_c). Hence, net reaction moves in backward direction.

Similarly, if ([B]) decreases, the numerator of (Q_c) decreases bringing down the value of (Q_c). This makes (Q_c < K_c). Hence, net reaction moves in forward direction.