Consider the following equilibrium:

4KO2 (s) + 2H2O (g) 4KOH (s) + 3O2 (g)

Which of the following is a correct equilibrium expression?

A.

'"K"_ ("eq") = (["KOH"]^4["O"_2]^3) / (["KO"_2]^4["H"_2"O"]^2) '

B.

'"K"_ ("eq") = (["H"_2"O"]^2) / (["O"_2]^3) '

C.

'"K"_ ("eq") = (["KO"_2]^4["H"_2"O"]^2) / (["KOH"]^4["O"_2]^3) '

D.

'"K"_ ("eq") = (["O"_2]^3) / (["H"_2"O"]^2) '

Keq = [KOH]^4 [O2]^3/[[KO2]^4

Explanation:

4KO2 (s) + 2H2O (l) → 4KOH (s) + 3O2 (g)

Looking at the equation, the correct equilibrium expression is shown in the answer. The equilibrium constant for a reaction is given by the active masses of species involved in the reaction. The relative molar coefficients of species are raised to the power of their molar concentrations to give the active mass of each specie. This active mass now goes into the equilibrium equation.

Water is not included in the equilibrium equation because, as a solvent, it is present in large excess.