# Which of the following is incorrect about relationship between $K_p$ and $K_c$?

(a) When, $\Delta n_g = 0, K_p = K_c$

(b) When, $\Delta n_g > 0, K_p > K_c$

(c) When, $\Delta n_g < 0, K_p < K_c$

(d) When, $\Delta n_g > 0, K_p < K_c$

Toolbox:
• $K_p = K_c (RT)^{\Delta n_g}$

Answer: When, $\Delta n_g > 0, K_p < K_c$

Here, $\Delta n_g$ = change in the number of gaseous moles

When, $\Delta n_g = 0, K_p = K_c$
e.g., $H_2 (g) + I_2 (g) \rightleftharpoons 2HI (g)$

When, $\Delta n_g > 0, K_p > K_c$
e.g., $PCl_5 (g) \rightleftharpoons PCl_3 (g) Cl_2 (g); \Delta n_g = 2 - 1 = 1$

When, $\Delta n_g < 0, K_p < K_c$
e.g., $N_2 (g) + 3H_2 (g) \rightleftharpoons 2NH_3 (g); \Delta n_g = 2 - 4 = -2$

edited Nov 23, 2013