Page 184 - Chemical equilibria Volume 4

160 Chemical Equilibria
X is the partial molar value corresponding to variable X.
i
Let us now apply this relation to the reference solution. We obtain:
∂μ i 0 =− X 0 [A1.23]
∂ Y i

Such a relation applies, for example, to the influence of the pressure.
Remembering that variable Y is –P, we find:
∂μ i 0 = V 0 [A1.24]
∂ P i

V i 0 is the partial molar volume of the component in the reference
solution. In the case of reference (I), it is simply the molar volume of the
0
pure substance v .
i
A1.3. Characterization of the imperfection of a real solution by
the excess Gibbs energy

A second technique, which is being used increasingly widely, to define a
solution is to define its difference from the perfect solution by the excess
Gibbs energy.

A1.3.1. Definition of the excess values

*
Consider an extensive property J of a solution and call J the value that
the property would have in the given conditions of temperature and pressure
xs
if that solution were perfect. The excess value of J is the value J defined
by:

J xs = J − J * [A1.25]

xs
J is indeed characteristic of the difference of our real solution in
comparison to a perfect solution.