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When the species is the component of mixture phases, the concentration of the species will be calculated for the respective points and will be given in the Chemical Potential Table or the List of Points.

For simplicity, we consider the ideal asssociation mixture; the Gibbs energy of this mixture can be written as follows;

G_mix(AxByCz) = l μ(AB) + m μ(BC) + n μ(AC)        (1)
Here, the mixture consists of the components, AB, BC, and AC.
The chemical potentials of AB, BC, and AC can be written in terms of the elemental chemical potential values, μ(A) ... as folllows;

μ(AB) = μ(A) + μ(B)        (2)
μ(BC) = μ(B) + μ(C)        (3)
μ(AC) = μ(A) + μ(C)        (4)

Furthermore, the logrithmic activity of component AB can be calculated as
RT ln a(AB) = μ(AB) - μ°(AB)        (5)
The total Gibbs energy of the mixture can be written as
G_mix(AxByCz) = l μ°(AB) + m μ°(BC) + n μ°(AC)

+RT{l ln a(AB) +m ln a(BC) +n ln a(AC) }        (6)
In the ideal mixture, the concetration is equal to the activity. Thus, the above equation becomes for the ideal mixture in which the concetration of respective components is given as the activity.

Therefore, at the equilibrium point, all species can have the fixed chemical potential values. In equaatiaon (1), the constants, l, m, and n are related to the concentrations of these constituents. Actually, l/(l+m+n), m/(l+m+n), n/(l+m+n) are the concetrations of respective constituents, AB, BC, and AC at the point.

Note that even when the mixture cannot exist as the stable phase, the chemical potential values and also the concentrations can be evaluated and will be shown.