Lippman's equation

https://doi.org/10.1351/goldbook.L03577
An equation which gives the
electric charge
per unit area of an
interface
(electrode): (γEA)T,p,μiμ=QA where γ is the
interfacial tension
, EA is the potential of a cell in which the
reference electrode
has an interfacial equilibrium with one of the ionic components of A, QA is the charge on unit area of the
interface
, μi is the
chemical potential
of the combination of species i whose net charge is zero, T is the
thermodynamic temperature
and p is the external pressure. Since more than one type of
reference electrode
may be chosen, more than one quantity Q may be obtained. Consequently Q cannot be considered as equivalent to the physical charge on a particular region of the
interphase
. It is in fact an alternative way of expressing a
surface excess
or combination of
surface excess
of charged species.
Sources:
PAC, 1974, 37, 499. (Electrochemical nomenclature) on page 508 [Terms] [Paper]
PAC, 1986, 58, 437. (Interphases in systems of conducting phases (Recommendations 1985)) on page 445 [Terms] [Paper]