Mass Action Expression
What is Mass Action Expression?
The mass action expression is the ratio of the concentrations (or partial pressures) of products to reactants, each raised to the power of its stoichiometric coefficient, for a given chemical reaction. For the reaction aA + bB ⇌ cC + dD, it is Q = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ. When Q equals the equilibrium constant K, the system is at equilibrium; when Q < K the reaction proceeds forward, and when Q > K it proceeds in reverse.
Key Facts
Frequently Asked Questions
The mass action expression is the ratio of the concentrations (or partial pressures) of products to reactants, each raised to the power of its stoichiometric coefficient, for a given chemical reaction. For the reaction aA + bB ⇌ cC + dD, it is Q = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ. When Q equals the equilibrium constant K, the system is at equilibrium; when Q < K the reaction proceeds forward, and when Q > K it proceeds in reverse.