An amount of solid NH4HS is placed in a flask already containing ammonia

Discussion Forum : Chemical Equilibrium

Question -

An amount of solid $N H_{4} H S$ is placed in a flask already containing ammonia gas at a certain temperature and $0.50$ atm pressure. Ammonium hydrogen sulphide decomposes to yield $N H_{3}$ and $H_{2} S$ gases in the flask. When the decomposition reaction reaches equilibrium, the total pressure in the flask rises to $0.84$ atm. The equilibrium constant for $N H_{4} H S$ decomposition at this temperature is

Options:

A . 0.30

B . 0.18

C . 0.17

D . 0.11

Answer: Option D
:
D

$N H_{4} H S (s) ⇋ N H_{3} (g) + H_{2} S (g)$
$\begin{matrix} I n i t i a l l y, & a & 0.5 a t m & 0 a t e q u i l i b r i u m & . . . . . . & 0.5 + x & x \end{matrix}$
Total Pressure at eqilibrium $= 0.5 + x + x = 0.84$
$\Rightarrow x = 0.17$
$K_{p} = P_{N H_{3}} (g) \times P_{H_{2} S} (g) = (0.5 + x) x = (0.5 + 0.17) \times 0.17 = 0.1139 a t m^{2}$

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