Question

When sulphur in the form of $S_8$ is heated at $900K$ and constant volume, the initial pressure of $1atm$ increases by $27$% at equilibrium. This is because of conversion of some $S_8$ to $S_2$. Find the value of the equilibrium constant for this reaction.

Answer 1

$S_8\left(g\right)\rightleftharpoons 4S_2\left(g\right)$
Initial mole: $1$ $0$
At $e{q}^m$: $1-x$ $4x$

$\therefore$ Total Pressure $=1+3x=1.27$

$\Rightarrow x=0.09$
Applying law of mass action,
$K_p=\frac{{\left[p_{S_2}\right]}^4}{\left[p_{S_2}\right]}=\frac{{0.36}^4}{0.91}=0.01846$