Fugacities
Let us start from the definitions of Helmholtz and Gibbs free energies A and G using the inner energy U, the enthalpy H and the entropy S.
(1)
(2)
In the following the partial derivatives of A and G in respect to P and T at constant composition ni
(3)
(4)
(5)
and the chemical potentials µi
(6)
are used.
