# Free Energy

## Definition - What does Free Energy mean?

A system that operates thermodynamically possesses free energy, which is the amount of work that can be done by this thermodynamic system. Free energy can also be stated as the difference between the internal energy and un-useful energy that cannot be used to perform any work. Per the first law of thermodynamics, free energy is that energy that is available to perform any sort of work.

## Corrosionpedia explains Free Energy

The first law of thermodynamics states that the total energy of any isolated system is constant, which means that energy can neither be created nor can it be destroyed, but it can be converted from one form to another (i.e., the energy is always conserved). Some of the various measures of free energy functions are:

- Helmholtz free energy – Per this free energy system, at a constant volume and temperature, the free energy can be converted into work. This system is expressed by the equation:

A = U – T x S

where A is Helmholtz free energy

U is the internal energy of the system

S is entropy

T is absolute temperature

- Gibbs free energy – Per this free energy system, at a constant pressure and temperature, the free energy can be converted into work. This system is expressed by the equation:

G = H – T x S

where G is Gibbs energy

H is enthalpy

S is entropy

T is absolute temperature