Write the balanced chemical equation
Identify the equilibrium concentrations or partial pressures of reactants and products
Use the equilibrium expression for the reaction
For a general reaction aA + bB ⇌ cC + dD, write Keq = [C]^c[D]^d / [A]^a[B]^b
Use concentrations in mol/L for Kc
Use partial pressures for Kp
Substitute the equilibrium values into the expression
Calculate the ratio
Exclude pure solids and pure liquids from the expression
Keep each concentration or pressure raised to its stoichiometric coefficient
If needed, convert between Kp and Kc using Kp = Kc(RT)^(Δn)
Use the equilibrium constant at the specified temperature only