Question

Consider the following reaction:

2CH4(g)⇌C2H2(g)+3H2(g)

The reaction of CH4 is carried out at some temperature with an initial concentration of [CH4]=0.085M. At equilibrium, the concentration of H2 is 0.018 M.

Find the equilibrium constant at this temperature.

Express your answer using two significant figures.

Answer 1

Let's prepare the ICE table

[CH4] [C2H2] [H2]

initial 0.085 0 0

change -2x +1x +3x

equilibrium 0.085-2x +1x +3x

To find x, we will use the equilibrium concentration provided in the question

[H2] = 0.018

+3x = 0.018

x = 0.006

Equilibrium constant expression is

Kc = [C2H2][H2]^3/[CH4]^2

Kc = (+1x)(+3x)^3/(0.085-2x)^2

Kc = (+1*0.006)(+3*0.006)^3/(0.085-2*0.006)^2

Kc = 6.57*10^-6

Answer: 6.6*10^-6