Kp = Kc × (RT)^Δn
For gas-phase reactions, the equilibrium constant can be expressed in terms of partial pressures: Kp = Πp(products)^coeff / Πp(reactants)^coeff. Kp relates to Kc by Kp = Kc(RT)^Δn, where Δn = total moles of gaseous products minus gaseous reactants, R = 0.08206 L·atm/(mol·K). When Δn = 0, Kp = Kc. Kp is dimensionless only when pressures are divided by the standard pressure (1 atm or 1 bar). Like Kc, Kp depends only on temperature and is related to Gibbs energy: ΔG° = −RT ln(Kp). For the Haber process N₂ + 3H₂ ⇌ 2NH₃, Δn = 2−4 = −2, so high pressure favors products (Le Chatelier's principle), which is why industrial synthesis operates at 150-300 atm.