A
thermodynamic potential is a
scalar quantity used to represent the
thermodynamic state of a
system. The concept of thermodynamic potentials was introduced by
Pierre Duhem in 1886.
Josiah Willard Gibbs in his papers used the term
fundamental functions. One main thermodynamic potential that has a physical interpretation is the
internal energy . It is the energy of configuration of a given system of
conservative forces (that is why it is a potential) and only has meaning with respect to a defined set of references (or data). Expressions for all other thermodynamic energy potentials are derivable via
Legendre transforms from an expression for . In
thermodynamics, certain forces, such as
gravity, are typically disregarded when formulating expressions for potentials. For example, while all the
working fluid in a
steam engine may have higher energy due to gravity while sitting on top of
Mount Everest than it would at the bottom of the
Mariana Trench, the
gravitational potential energy term in the formula for the internal energy would usually be ignored because
changes in gravitational potential within the engine during operation would be negligible.