Free Energy and Useful Work

The term represents the portion of an energy change (H) that is available to do useful work. If H is the total energy in a reaction, then G = H -TS indicates that part of H is alway dissipated as heat (the TS term) and is therefore unavailable for other things, such as muscle contraction, ion transport, or tissue growth. The remaining amount () is available for useful work, but may not actually be fully utilized for useful work because the efficiency of a process (the ratio of work actually accomplished to , the maximum work available) is always less than 100%.

See also: Internal Energy (E), Enthalpy, Interplay of Enthalpy and Entropy