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#### A

Thermodynamic excess properties defined relative to a Gibbs surface.

Surface excess energy ( ) is defined by

where and satisfy the condition

the total volume of the system.

and are the energy densities in the two bulk phases where and are the mean molar energies and and are the mean molar volumes of the two phases.

Surface excess entropy ( ) is defined by

and are the entropy densities in the two bulk phases, where and are the mean molar entropies of the two phases.

Surface excess Helmholtz energy ( ) is defined by

Surface excess enthalpy ( ) is defined by

Surface excess Gibbs energy ( ) is defined by

When the thermodynamics of surfaces is discussed in terms of excess quantities, . There is thus only one way of defining the excess surface enthalpy and excess surface Gibbs energy (cf. case B, below).

The corresponding excess quantities per unit area may be denoted by lower case letters:

Quantities invariant to the choice of dividing surface may be defined as follows:

Relative (excess) surface energy (with respect to component 1)

Analogous equations hold for , , and .

Reduced (excess) surface energy

where is the total adsorption relative to an arbitrary choice of dividing surface and and are the total concentrations of the two phases.

Analogous equations hold for , , and .

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2002-09-05