Measure of the total combined energies within a system, derived from heats of transformation, disorder, and other forms of internal energy (e.g., electrostatic charges).
A system will change spontaneously to achieve a lower total free energy. Thus, free energy is the driving force toward equilibrium conditions. The change in free energy between an initial and a final state is useful in evaluating certain thermodynamic processes and can be used to judge whether transformations will occur spontaneously. There are two forms of free energy, with different definitions and applications: the Helmholtz (see Hermann von Helmholtz ) free energy, sometimes called the work function, and the Gibbs (see J. Willard Gibbs ) free energy.