Helmholtz Free Energy

The Helmholtz free energy is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal).

The equation for the Helmholtz free energy is F = U – TS, where U is the internal energy, T is the temperature, and S is the entropy.

The difference between the Helmholtz free energy and the Gibbs free energy is that the Helmholtz free energy is defined at constant temperature and volume, while the Gibbs free energy is defined at constant temperature and pressure.

The applications of the Helmholtz free energy include determining the equilibrium state of a system, calculating the maximum amount of work that a system can do, and predicting the spontaneity of a reaction.

For more information, please see the following resources:

• Wikipedia article on Helmholtz free energy
• Khan Academy tutorial on Helmholtz free energy
• Texas A&M University lecture notes on Helmholtz free energy