Question

For which of the following reaction, $K_p=K_c$ ?

• A. $2\mathrm{NOCl}(\mathrm{g})\rightleftharpoons 2\mathrm{NO}(\mathrm{g})+{\mathrm{Cl}}_2(\mathrm{g})$
• B. ${\mathrm{N}}_2(\mathrm{g})+3{\mathrm{H}}_2(\mathrm{g})\rightleftharpoons 2{\mathrm{NH}}_3(\mathrm{g})$
• C. ${\mathrm{H}}_2(\mathrm{g})+{\mathrm{Cl}}_2(\mathrm{g})\rightleftharpoons 2\mathrm{HCl}(\mathrm{g})$
• D. ${\mathrm{PCl}}_3(\mathrm{g})+{\mathrm{Cl}}_2(\mathrm{g})\rightleftharpoons {\mathrm{PCl}}_5(\mathrm{g})$

Answer 1

Answer: (C)

${\mathrm{K}}_{\mathrm{p}}={\mathrm{K}}_{\mathrm{c}}\times (\mathrm{RT}{)}^{\Delta {\mathrm{n}}_{(\mathrm{g})}}$

$\Delta n_{(g)}=$ Sum of gaseous products $-$ Sum of gaseous reactants $K_p=K_c$ when $\Delta n_{(g)}=0$

$\Delta n_{(g)}=2-2=0$

So the correct option is $H_2(g)+C{l}_2(g)\rightleftharpoons 2HCl(g)$

In rest other options $K_p$ and $K_c$ can not be equal as $\Delta n_{(g)}$ is not zero.