In thermodynamics, four different quantities, measured in units of energy, are called thermodynamic potentials:
- Internal energy U, which is the energy needed to create a system
- Helmholtz free energy F, given by F=U-TS
- Enthalpy H, given by H=U+pV
- Gibbs free energy G, given by G=U+pV-TS
Constant V | Constant p | |
---|---|---|
Constant S | ΔU | ΔH |
Constant T | ΔF | ΔG |
Most commonly one considers reactions at constant p and T, so the Gibbs free energy is the most useful potential in studies of chemical reactions.