#### Learning Objective

- Discuss the relationship between free energy and pressure.

#### Key Points

- Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature.
- The Gibbs free energy equation is dependent on pressure.
- It is a convenient criterion of spontaneity for processes with constant pressure and temperature.

#### Term

- chemical potentialIn thermodynamics, chemical potential, also known as partial molar free energy, is a form of potential energy that can be absorbed or released during a chemical reaction.

Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure. Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings. The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.

When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force. Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature. As such, it is a convenient criterion of spontaneity for processes with constant pressure and temperature. Therefore, Gibbs free energy is most useful for thermochemical processes at constant temperature and pressure.