Question

Which is the correct statement if${N_2}$ is added to equilibrium condition?

A. The equilibrium will shift to forward direction because according to the second law of thermodynamics the entropy must increase in the direction of the spontaneous reaction.
B. The condition for equilibrium is ${G_{{N_2}}} + 3{G_{{H_2}}} = 2{G_{N{H_3}}}$ where Gibbs free energy per mole of the gaseous species measured at the partial pressure. The condition of equilibrium is unaffected by the use of a catalyst, which increases the rate of both the forward and backward reactions to the same extent.
C. the catalyst will increase the rate of forward reaction by $\alpha$ and that of the backward reaction by $\beta$
D. catalyst will not alter the rate of either of the reactions.

Answer 1

the above equation is an example of chemical equilibrium that is the concentration of reactant and product does not change with time. The equilibrium is dynamic and can continue in both forward and backward directions, though the rate of forward reaction is equal to the rate of backward reaction.

Complete step by step solution: Let’s analyze the statement one by one. Since we are given a condition where we add nitrogen to the equation hence we are increasing the concentration of reactants in the state of equilibrium then according to Le Chatelier's Principle on increasing the concentration of reactants the equilibrium shifts in forward direction and on increasing the concentration of products the equilibrium shifts in the backward direction to nullify the effect of the added reactant. Hence option A is wrong as the equilibrium shifts in forward direction but not due to the second law of thermodynamics.

As stated Gibbs energy is measured in thermodynamics to interrogate the spontaneity of the reaction it is zero if the reaction has achieved equilibrium and there is no longer any energy to drive the reaction in forward or backward direction hence the catalyst does not affect the equilibrium in this particular condition. Hence the correct option is option B.

A catalyst can fasten the approach of equilibrium but does not alter the state of equilibrium. Since the concentration of products and reactants remain the same after attaining equilibrium but nitrogen is added to increase the concentration of the reactants the catalyst will increase the rate of reaction in both the directions by the same extent.
Hence the only correct option is B.

Note: If the reaction is spontaneous and proceeds in forward direction then Gibbs energy is negative and if the reaction is non spontaneous then Gibbs energy is positive.