Relation between Kp and Kc

For a general gas phase reaction at equilibrium:

a A (g) + b B (g) ⇌ c C (g) + d D (g)

For a gaseous substance i, the ideal gas equation is

piV = niRT

ci = ni/V

pi = ciRT

This relation can be used for replacing the partial pressure terms in the expression for Kp.

where Δng is the change in the moles of gaseous substances in the reaction and is equal to the difference in the moles of gaseous products nP and the moles of gaseous reactants, nR. It may be zero, positive or negative.