Question

A sample of gas in which [h2s] = 3.50 m is heated to 1400 k in a sealed vessel. after chemical equilibrium has been achieved, what is the value of [h2s]? assume no h2 or s2 was present in the original sample.

Answer 1

The value of Kc for the thermal decomposition of H₂S is 2.2 x 10⁻⁴ at 1400 K:
                        2 H₂S(g) ↔     2 H₂(g) + S₂(g)
initial                  3.5 M               0           0
at equilibrium     3.5 M - 2x       2x          x
Kc             = [S₂][H₂]² / [H₂S]² 
2.2 X 10⁻⁴ = x(2x)² / (3.5 - 2x)²
2.2 x 10⁻⁴ = 4 x³ / (3.5)² Assuming x <<<<< 3.5
x = 0.088
Thus [H₂S] = 3.324 M