Equilibrium constant has units if

Explanation

The equilibrium constant (Kc for concentration-based, Kp for pressure-based) has units only when the number of moles of reactants and products in the balanced chemical equation are not equal.Kc and Kp expressions:Kc = [products]^coefficients / [reactants]^coefficients (units of (mol/L))Kp = (products)^coefficients / (reactants)^coefficients (units of (atm))Units cancellation:If the number of moles of reactants and products is equal, their stoichiometric coefficients will also be equal. When these coefficients are multiplied by their respective concentrations or pressures, the units will cancel out, resulting in a unitless Kc or Kp.Units when mole numbers are unequal:If the number of moles of reactants and products is unequal, their stoichiometric coefficients won't necessarily be equal. Consequently, the units won't cancel out completely, and Kc or Kp will have units determined by the difference in stoichiometric coefficients (Δn) in the balanced equation:Kc: (mol/L)^(Δn)Kp: (atm)^(Δn)Example:Consider the reaction: N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)At equilibrium, Kc has units of (mol/L)^(-2) because Δn = (2 mol NH₃) - (1 mol N₂ + 3 mol H₂) = -2.