A form of the Gibbs adsorption equation which includes an expression of the phenomenon of electrocapillarity: \[s\ \mathrm{d}T- \tau \ \mathrm{d}p+\mathrm{d}\gamma +\sigma ^{\alpha }\ \mathrm{d}E+\sum \mathit{\Gamma }_{j}\ \mathrm{d}\mu _{j}=0\] where s is the surface excess of entropy of unit area of interphase, T is the temperature, τ is the thickness or excess volume of unit area of the interphase, p is the external pressure, γ is the interfacial tension, σ^α is the free surface charge density on phase α (areal amount of charge on the surface of phase α), E is the generalized potential, Γj is the surface excess, µj is the chemical potential and j is an electrically neutral component of one or other of the phases; the sum is over all the components but one in each phase.