Practice Problem Answers

Write an equilibrium expression for each of the following reactions.

1) 3O2 ⇌ 2O3

Keq=[O3]2[O2]3

2) N2 + 3H2 ⇌ 2NH3

Keq=[NH3]2[N2][H2]3

3) H2 + I2 ⇌ 2HI

Keq=[HI]2[H2][I2]

4) PCl5 ⇌ PCl3 + Cl2

Keq=[PCl3][Cl2][PCl5]

5) SO2 + (1/2)O2 ⇌ SO3

Keq=[SO3][SO2][O2]1/2

Notice that this last problem (#5) is the second example equation in the tutorial, with the coefficients divided through by 2. The result is the square root of each concentration value and so the value to the Keq in #5 is the square root of the value in the second example problem.

What's the point? Well, the point is that, when discussing an equilibrium constant, the relevant chemical equation must also be included in the discussion.