Consider the following reaction:

NH4HS (s) ⇌NH3 (g) + H2S (g)

An equilibrium mixture of this reaction at a certain temperature was found to have [NH3] = 0.276 M and [H2S] = 0.370 M. What is the value of the equilibrium constant (Kc) at this temperature?

Kc = 0.102

Explanation:

NH₄HS (s) ⇌ NH₃ (g) + H₂S (g)

The equilibrium constant for the above reaction, can be written as the product of the concentration of product raised to the power of stoichiometric coefficients in a balanced equation of dissociation divided by the product of the concentration of reactant raised to the power of stoichiometric coefficients in the balanced equation of dissociation.

Hence,

Kc = [ NH₃ (g) ][ H₂S (g) ] / [ NH₄HS (s) ]

Since, the state of NH₄HS is solid so, it's concentration will remain constant, hence, the equation can be rearranged as -

Kc = [ NH₃ (g) ][ H₂S (g) ]

From the question,

[ NH₃ (g) ] = 0.276 M

[ H2S (g) ] = 0.370 M

Now, putting it in the above equation,

Kc = [ NH₃ (g) ][ H₂S (g) ]

Kc = 0.276 * 0.370

Kc = 0.102