This page develops the Helmholtz free energy from the point of view of thermal and statistical physics. For applications to chemistry, see work content.

The Helmholtz free energy is a state function of a system defined as

F = U - TS

where F is the Helmholtz free energy in joules,

U is the energy of the system in joules,

T is the temperature in kelvin,

and S is the entropy in joules per kelvin.

Note: in some literature, this quantity is referred to as A.