Free Energy

Gibbs Free Energy

Gibbs free energy is the amount of energy available to do work on a system. Given by

$G=H-TS$ $H$ represents the enthalpy of the system, $T$ is the temperature and $S$ is the entropy. This is used when a system is at constant pressure.

Hemholtz Free Energy

Helmholtz free energy is the amount of energy available to do work on a system. Given by

$F=U-TS$

$U$ represents the internal energy of the system, $T$ is the temperature and $S$ is the entropy. This is used when a system is at constant volume.