Chemical and Ionic Equilibrium 1 Question 42
44. When $3.06 \mathrm{~g}$ of solid $\mathrm{NH}_{4} \mathrm{SH}$ is introduced into a two litre evacuated flask at $27^{\circ} \mathrm{C}, 30 %$ of the solid decomposes into gaseous ammonia and hydrogen sulphide.
(i) Calculate $K_{c}$ and $K_{p}$ for the reaction at $27^{\circ} \mathrm{C}$.
(ii) What would happen to the equilibrium when more solid $\mathrm{NH}_{4} \mathrm{SH}$ is introduced into the flask?
$(1999,7 \mathrm{M})$
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Solution:
- (i) Mole of solid $\mathrm{NH}_{4} \mathrm{HS}$ taken initially $=\frac{3.06}{51}=0.06$
$$ \begin{aligned} & \text { At equilibrium } \mathrm{NH}{4} \mathrm{HS}(s) \rightleftharpoons \underset{0.018}{\mathrm{NH}{3}(g)+} \mathrm{H}{2} \mathrm{~S}(g) \ & K{c}=\left(\frac{0.018}{2}\right)^{2}=8.1 \times 10^{-5} \ & p\left(\mathrm{NH}{3}\right)=\frac{0.018 \times 0.082 \times 300}{2}=0.22 \mathrm{~atm} \ & K{p}=(0.22)^{2}=4.84 \times 10^{-2} \end{aligned} $$
(ii) Addition of solid $\mathrm{NH}_{4} \mathrm{HS}$ will have no effect on equilibrium.
