Question

Kc for the reaction of hydrogen and iodine to produce hydrogen iodide. H2(g) + I2(g) ⇌ 2HI(g) is 54.3 at 430 ° C. Calculate the equilibrium concentrations of H2, I2, and HI at 430 ° C if the initial concentrations are [H2] = [I2] = 0 M, and [HI] = 0.445 M.

Answer 1

H2 (g)    +   I2 (g)   <—>   2 HI (g)

0           0           0.445       (initial)

x           x           0.445-2x   (at equilibrium)

Kc = [HI]^2 / [H2][I2]

54.3 = (0.445-2x)^2 / x^2

sqrt(54.3) = (0.445-2x) / x

7.37 = (0.445-2x) / x

7.37*x = 0.445 - 2x

9.37*x = 0.445

x = 0.0475 M

At equilibrium:

[H2] = x = 0.0475 M

[I2] = x = 0.0475 M

[HI] = 0.445 - 2x = 0.445 - 2*0.0475 = 0.350 M