Chemical and Ionic Equilibrium - Result Question 100
####44. When $3.06 g$ of solid $NH _4 SH$ is introduced into a two litre evacuated flask at $27^{\circ} C, 30 %$ of the solid decomposes into gaseous ammonia and hydrogen sulphide.
(i) Calculate $K _c$ and $K _p$ for the reaction at $27^{\circ} C$.
(ii) What would happen to the equilibrium when more solid $NH _4 SH$ is introduced into the flask?
$(1999,7 M)$
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Solution:
- (i) Mole of solid $NH _4 HS$ taken initially $=\frac{3.06}{51}=0.06$
$$ \begin{aligned} & \text { At equilibrium } NH _4 HS(s) \rightleftharpoons \underset{0.018}{NH _3(g)+} H _2 S(g) \ & K _c=\left(\frac{0.018}{2}\right)^{2}=8.1 \times 10^{-5} \ & p\left(NH _3\right)=\frac{0.018 \times 0.082 \times 300}{2}=0.22 atm \ & K _p=(0.22)^{2}=4.84 \times 10^{-2} \end{aligned} $$
(ii) Addition of solid $NH _4 HS$ will have no effect on equilibrium.
