Question

The equilibrium below is established by placing solid NH₄HS in an evacuated container at 25 ⁰C. At equilibrium, some solid NH₄HS remains in the container.

                       NH₄HS(s) « NH₃(g) + H₂S(g) delta H⁰ = +93 kilojoules

Predict and rationalize, using LCP only, each of the following.

1. The effect on the equilibrium partial pressure of NH₃ gas when additional solid H₂S is introduced into the container.
2. The effect on the mass of solid NH₄HS present when the volume of the container is decreased.
3. The effect on the mass of solid NH₄HS present when the temperature is increased.

Answer 1

Part (i).

There is no effect on the equilibrium partial pressure of NH₃ gas when additional solid H₂S is introduced into the container.

Explanation: Solids won't affect the equilibrium as their contribution is negligible when compared to the effect of gases.

Part (ii).

There is no effect on the mass of solid NH₄HS present when the volume of the container is decreased.

Explanation: The mass of solid won't be affected as they occupy very less space/volume.

Part (iii).

There is no effect on the mass of solid NH₄HS present when the temperature is increased.

Explanation: The mass of solid won't be affected as the solid term is not involved in the equilibrium expression.

Note: Kp = P_NH3 * P_H2S