
Excess molar quantity
Encyclopedia
Excess molar quantities are properties of mixtures which characterize the nonideal behaviour of real mixtures. They are the difference between the partial molar property of a component in a mixture and that of the pure component. The most frequently used excess molar quantities are the excess molar volume, excess molar enthalpies and heat capacities, excess chemical potential
.

Here
denotes the pure substance,
the excess molar property, and
corresponds to the specific property under consideration. From the definition of partial molar properties,

substitution yields:
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 ....
.
Definition
By definition, excess properties of a mixture are related to those of the pure substance by:
Here




substitution yields:
