6 Nitrogen and hydrogen react according to the reaction belo

6. Nitrogen and hydrogen react according to the reaction below to form ammonia: N2(g) 3H2 (g) 2 NH3 (g) Kc= 4.51 x 10-5 at 450°C + The concentration of ammonia is 0.250M. Calculate the equilibrium concentration of H2.

Solution

For the given reaction,

Kc = [NH3]^2/[N2][H2]^3 = 4.51 x 10^-5

ICE chart

            N2 + 3H2 <====>   2NH3

I            -          -                    0.250

C         +x       +3x                    -2x

E           x        3x                 0.250-2x

So,

4.51 x 10^-5 = (0.250-2x)^2/(x)(3x)^3

1.22 x 10^-3x^3 - 4x^2 + x - 0.0625 = 0

x = 0.125 M

So,

equilibrium concentration of [H2] = 3 x 0.125 = 0.375 M