Write the balanced chemical equation
Include only gaseous substances in the expression
Use partial pressures for each gas
Put products in the numerator
Put reactants in the denominator
Raise each pressure term to its stoichiometric coefficient
Omit pure solids and pure liquids
Use (K_p) for the pressure equilibrium constant
Example form: (K_p = dfrac{(P_{text{products}})^{text{coefficients}}}{(P_{text{reactants}})^{text{coefficients}}})