Question

For, $Zn\left(s\right)+2HCl\left(aq\right)\rightleftharpoons ZnC{l}_2\left(aq\right)+H_2\left(g\right)$
what will be the expression of $K_c$:

• A. $K_c$ = $\left[H_2\right]$
• B. $K_c$ = $\frac{\left[H_2\right]\left[ZnC{l}_2\right]}{[HCl{]}^2}$
• C. $K_c$ = $\frac{\left[H_2\right]}{\left[HCl\right]}$
• D. $K_c$ = $\frac{\left[H_2\right]\left[ZnC{l}_2\right]}{\left[HCl\right]\left[Zn\right]}$

Answer 1

The correct option is B $K_c$ = $\frac{\left[H_2\right]\left[ZnC{l}_2\right]}{[HCl{]}^2}$

This is an example of heterogenous reaction.
So, considering active masses for pure solids as constant.
$K_c$ is written as using law of mass action :

$K_c$ = $\frac{\left[H_2\right]\left[ZnC{l}_2\right]}{[HCl{]}^2}$