The equilibrium pressure of ${\text{NH}}_{\text{4}}\text{CN(s)}\underset{ }{\overset{ }{\rightleftharpoons }}{\text{NH}}_{\text{3}}\left(\text{g}\right)+\text{HCN(g)}$ is 0.298 atm. If  $N{H}_{4}CN\left(s\right)$ is allowed to decomposed in presence of  ${\text{NH}}_{\text{3}}$ at  $\text{0.25}$ atm. Calculate partial pressure of  $\text{HCN}$ at equilibrium

${\text{NH}}_4\text{CN}\left(\text{s}\right)\underset{ }{\rightleftharpoons }\underset{\text{P}}{{\text{NH}}_3}\left(\text{ g}\right)+\underset{\text{P}}{\text{HCN}}\left(\text{g}\right)$

At eq.
$\therefore$ Total pressure  $=2\text{P}=0.298\text{ atm p}=0.149$
Also  ${\text{K}}_{\text{P}}={\text{P}}_{{\text{NH}}_3}^1\times {\text{P}}_{\text{HCN}}^1=0.149\times 0.149=0.022{\text{ atm}}^2$
Now ${\text{P}}_{{\text{NH}}_3}=0.25\text{ atm}$

${\text{NH}}_4\text{CN}\left(\text{s}\right)\rightleftharpoons {\text{NH}}_3\left(\text{ g}\right)+\text{HCN}\left(\text{g}\right)$

$\begin{array}{lll}\text{ Initial }& 0.25& 0\\ \text{ At eq }& 0.25+{\text{P}}^1& {\text{P}}^1\\ {\text{ K}}_{\text{P}}={\text{P}}^1(0.25+{\text{P}}^1)& & \\ {\text{P}}^1=0.0694\text{ atm}& & \end{array}$