Question

For which one of the following reactions $K_p=K_c?$

• A. $PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$
• B. $N_2+O_2\rightleftharpoons 2NO$
• C. $N_2+3H_2\rightleftharpoons 2N{H}_3$
• D. $2S{O}_3\rightleftharpoons 2S{O}_2+O_2$

Answer 1

Answer: (B)

$K_p=K_c(RT{)}^{\Delta n_g}$
$K_p=K_c$ only when $(RT{)}^{\Delta n}=0$
(a) $PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$
$\Delta n_g=n_p-n_g$
$=2-1$
$=1$
$\therefore \Delta K_p\ne K_c$
(b) $N_2+3O_2\rightleftharpoons 2NO$
$\Delta n_g=2-2$
$=0$
$\therefore K_p=K_c$
(c) $N_2+3H_2\rightleftharpoons 2N{H}_3$
$\Delta n_g=2-4$
$=-2$
$\therefore K_p\ne K_c$
(d) $2S{O}_3\rightleftharpoons 2S{O}_2+O_2$
$\Delta n_g=3-2=1$
$\therefore K_p\ne K_c$