2026 EquilibriumRelationship between $K_p$ and $K_c$ Medium Question 4 of 104 in Equilibrium

Given below are certain reactions. Identify the reaction for which $K_p \neq K_c$.

A $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$
B $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$
C $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$
D $H_2O(g) + CO(g) \rightleftharpoons H_2(g) + CO_2(g)$

The answer is C.

Solution

$K_p = K_c(RT)^{\Delta n_g}$; $K_p \neq K_c$ only when $\Delta n_g \neq 0$ $N_2(g) + O_2(g) \rightleftharpoons 2NO(g)$: $\Delta n_g = 0$ $H_2O(g) + CO(g) \rightleftharpoons H_2(g) + CO_2(g)$: $\Delta n_g = 0$ $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$: $\Delta n_g = -2$ $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$: $\Delta n_g = 0$ So $K_p \neq K_c$ for $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

Equilibrium in past papers

104 questions from this chapter have appeared across 27 exam years.