Equilibrium constant

Science

Definition

A value (K) that expresses the ratio of product concentrations to reactant concentrations at chemical equilibrium, each raised to the power of their coefficients. A large K means products are favored; a small K means reactants are favored.

Examples

  • The formation of water from hydrogen and oxygen has a very large K, favoring products
  • The dissociation of a weak acid like acetic acid has a small Ka
  • Comparing Q (reaction quotient) to K to predict which direction a reaction will shift
Key Fact

K = [products]^coefficients / [reactants]^coefficients at equilibrium

Related Terms

Le chatelier's principle Ice tables Free energy and equilibrium Reaction rates

Study This Concept

Practice equilibrium constant with free review games in these units:

AP Chemistry Unit 7: Equilibrium