Excess chemical potential

In thermodynamics, the excess chemical potential is defined as the difference between the chemical potential of a given species and that of an ideal gas under the same conditions (in particular, at the same pressure, temperature, and composition). The chemical potential of a particle species ${\displaystyle i}$ is therefore given by an ideal part and an excess part.

${\displaystyle \mu _{i}=\mu _{i}^{\text{ideal}}+\mu _{i}^{\text{excess}}}$

Chemical potential of a pure fluid can be estimated by the Widom insertion method.