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, $\tau$ is the thickness or excess volume of unit area of the interphase, $p$ is the external pressure, $\gamma$ is the interfacial tension, ${\sigma }^{\alpha }$ is the free surface charge density on phase $\alpha$ (areal amount of charge on the surface of phase $\alpha$), $E$ is the generalized potential, ${\mathit{\Gamma }}_j$ is the surface excess, ${\mu }_j$ 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.