Defined by:
where

is the
surface excess Helmholtz energy,

is the
surface excess Gibbs energy
is the interfacial Helmholtz energy,

is the interfacial Gibbs energy, and

is the surface area. The quantities thus defined can be shown to be identical, and
the conditions of equilibrium of component

in the system to be
where

and

are the
chemical potentials of

in the bulk phases
α and β.
(

or

have to be omitted from this equlibrium condition if component

is not present in the respective bulk phase.) The surface chemical potentials are
related to the
Gibbs energy functions by the equations
Source:
PAC, 1972, 31, 577
(Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix
II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry)
on page 602
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.