Free energy and equilibrium

Science

Definition

Gibbs free energy (G) determines whether a reaction is spontaneous. At equilibrium, ΔG = 0 and the system has no net change. The relationship between free energy and the equilibrium constant is given by ΔG° = −RT ln K.

Examples

  • A reaction with a large negative ΔG° has a large K and strongly favors products
  • At equilibrium, forward and reverse reaction rates are equal and ΔG = 0
  • ATP hydrolysis has a negative ΔG, making it spontaneous and useful for cellular work
Key Fact

ΔG° = −RT ln K; when ΔG = 0, the system is at equilibrium

Related Terms

Gibbs free energy Equilibrium constant Enthalpy Entropy

Study This Concept

Practice free energy and equilibrium with free review games in these units:

AP Chemistry Unit 9: Applications of Thermodynamics