Le chatelier's principle

Science

Definition

Le Chatelier's principle states that if a stress is applied to a system at equilibrium, the system will shift in the direction that partially counteracts the stress and re-establishes equilibrium. Stresses include changes in concentration, pressure, volume, or temperature.

Examples

  • Adding more N₂ to the Haber process shifts equilibrium toward producing more NH₃
  • Increasing temperature of an exothermic reaction shifts equilibrium toward the reactants
  • Decreasing volume of a gas-phase reaction shifts equilibrium toward the side with fewer moles of gas
Key Fact

The system shifts to oppose the applied stress; a catalyst does NOT shift equilibrium—it only speeds up both directions equally.

Related Terms

Equilibrium constant Ice tables Reaction rates Concentration

Study This Concept

Practice Le Chatelier's principle with free review games in these units:

AP Chemistry Unit 7: Equilibrium