Question

An amount of solid $NH_4HS$ is placed in a flask already containing ammonia gas at a certain temperature and 0.50 atm. pressure. Ammonium hydrogen sulphide decomposes to yield $NH_3$ and $H_2S$ 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 $NH_4HS$ decomposition at this temperature is

• A. 0.3
• B. 0.18
• C. 0.17
• D. 0.11

Answer 1

Answer: (D)

0.11

Answer 2

${NH_4HS (s) <=> NH_3(g) + H_2S (g)}$ If $x$ is the partial pressure of $H_2S$ formed at equilibrium. $(p_{NH_3})_{eqm} = (0.50 + x) atm$ $(p_{H_2})_{eqm} = x \,atm$ $(p_{NH_3})_{eqm} + (p_{H_2S})_{eqm} = 0.50 + x + x = 0.84$ $x 0.17$ atm $K_p = (p_{NH_3})_{eqm} \times (p_{H_2s})_{eqm}$ = (0.50 + 0.17) $\times$ 0.17 = 0.1139 = 0.11