Question

Consider the reaction for the decomposition of hydrogen disulfide:

2H2S(g)⇌2H2(g)+S2(g),  Kc=1.67×10−7 at 800∘C

The reaction is carried out at the same temperature with the following initial concentrations:

[H2S][H2][S2]===4.50×10−4M0.00M0.00M

Find the equilibrium concentration of S2.

Answer 1

From the data,

ICE chart

              2H2S (g) <=====> 2H2 (g) + S2 (g)

I          4.5 x 10^-4                   -               -

C             -2x                         +2x            +x

E       4.5 x 10^-4 - 2x             2x              x

So,

Kc = [H2]^2.[S2]/[H2S]^2

1.67 x 10^-7 = (2x)^2(x)/(4.5 x 10^-4 - 2x)^2

4x^3 - 6.7 x 10^-7x^2 + 3 x 10^-10x - 3.4 x 10^-14 = 0         

x = 1.9 x 10^-5 M

Equilibrium concentration of [S2] = 1.9 x 10^-5 M