We are being asked to calculate the equilibrium constant, K_{p}, for this reaction:

2 SO_{2}(g) + O_{2}(g) ⇌ 2 SO_{3}(g)

Recall that the ** equilibrium constant** is the ratio of the products and reactants. We use

$\overline{){{\mathbf{K}}}_{{\mathbf{p}}}{\mathbf{=}}\frac{{\mathbf{P}}_{\mathbf{products}}}{{\mathbf{P}}_{\mathbf{reactants}}}}$

▪ **only aqueous and gaseous species** are included in the equilibrium expression

▪ the **coefficient** of each compound in the reaction equation will be the **exponent **of the concentrations in the equilibrium expression

Consider the reaction: 2SO_{2}(g) + O_{2}(g) ⇌ 2SO_{3}(g)

When 0.60 atm of SO_{2} and 0.40 atm of O_{2} are placed in a container, the reaction proceeds and it is found that 0.50 atm of SO_{3} is produced at equilibrium. Calculate the value of K_{p} for this reaction.

A. 75

B. 33

C. 90

D. 120

E. 170