**Problem:**

For the reaction

H

_{2}(g) + I

_{2}(g) ↔ 2 HI(g)

At equilibrium, the concentrations are found to be

[H

_{2}] = 0.106 M

[I

_{2}] = 0.035 M

[HI] = 1.29 M

What is the equilibrium constant of this reaction?

**Solution**

The equilibrium constant (K) for the chemical equation

aA + bB ↔ cC + dD

can be expressed by the concentrations of A,B,C and D at equilibrium by the equation

K = [C]

^{c}[D]

^{d}/[A]

^{a}[B]

^{b}

For this equation, there is no dD so it is left out of the equation.

K = [C]

^{c}/[A]

^{a}[B]

^{b}

Substitute for this reaction

K = [HI]

^{2}/[H

_{2}][I

_{2}]

K = (1.29 M)

^{2}/(0.106 M)(0.035 M)

K = 4.49 x 10

^{2}

**Answer:**

The equilibrium constant of this reaction is 4.49 x 10

^{2}.