Excess chemical potential

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 ). The chemical potential of a particle species ${\displaystyle i}$ is therefore given by an ideal part and an excess part.

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

For a system of diameter ${\displaystyle L}$ and volume ${\displaystyle V}$, at constant temperature :${\displaystyle T}$, the classical canonical partition function ${\displaystyle Q(N,V,T)={\frac {V^{N}}{\Lambda ^{dN}N!}}\int _{0}^{1}\ldots \int _{0}^{1}ds^{N}\exp[-\beta U(s^{N};L)]}$ with ${\displaystyle s}$ a scaled coordinate.

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