Helmholtz free energy

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Helmholtz free energy

(Also called Helmholtz function, work function.) A thermodynamic function of state that, in a reversible isothermal process, increases with work done on the system.

In typical notation the Helmholtz free energy is
ams2001glos-He10
where F is the Helmholtz free energy (sometimes designated as A), U is the internal energy, T is temperature, and S is the entropy. By use of the first law of thermodynamics for reversible processes, the rate of change of the Helmholtz free energy is given by
ams2001glos-He11
where W is the work done by the system.
Compare Gibbs function.