Question

At a certain temperature, the Kp for the decomposition of H2S is 0.754. Initially, only H2S is present at a pressure of 0.139 atm in a closed container. What is the total pressure in the container at equilibrium?

Answer 1

The decomposition of H2S happens in the following reaction scheme.

It is given that the equilibrium constant Kp is

For a generic reaction of gases.

The expression of Kp in terms of the partial pressure of the reactant and products at equilibrium is

For us initial partial pressure of H2S = 0.139 atm. There are no H2 or S2 present initially.

We can create an ICE table to determine the equilibrium partial pressures of all species.

Initial, atm	0.139	0	0
Change, atm	-2x	+2x	+x
Equilibrium, atm	0.139-2x	2x	x

Hence, the Kp expression for our equilibrium is

Hence, total pressure at equilibrium is