Question

Consider the following equilibria:
(1) $N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2N{H}_3\left(g\right)$
(2) $N_2\left(g\right)+O_2\left(g\right)\rightleftharpoons 2NO\left(g\right)$
(3) $PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$
Choose the correct statement(s):

• A. Addition of an inert gas at constant volume has no effect on equilibria in (2).
• B. Addition of an inert gas at constant pressure favours the forward reaction in (3), backward reaction in (1) and has no effect on (2).
• C. Addition of an inert gas at constant pressure has no effect on equilibrium (2), but favours the forward reaction in (1) and backward reaction in (3).
• D. Addition of inert gas has no effect on all the three equilibria at constant temperature and also at constant pressure.

Answer 1

Answer: (A), (B)

Addition of an inert gas at constant volume has no effect on equilibria in (2).
Addition of an inert gas at constant pressure favours the forward reaction in (3), backward reaction in (1) and has no effect on (2).

The addition of the inert gas at constant volume, has no effect on the equilibrium of the reaction (2). This is because, the number of moles of reactants and products is same.
When inert gas is added at constant presure, the equilibrium will shift in the direction in which there is increase in the number of moles of gases.
The number of moles increases for the forward reaction in (3) and backward reaction in (1). But the number of moles of reactants and products are same for (2).
Hence, addition of an inert gas at constant pressure favors the forward reaction in (3), backward reaction in (1) and has no effect on (2).