A term used to quantify the difference in the free energy of a solute ion in two different standard states often in two different liquid phases. The relationship is ${\mathrm{\Delta }}_{\text{t}}{G}^{\text{⚬}}=\nu RT\ln {\gamma }_{\text{t}}$ where ${\mathrm{\Delta }}_{\text{t}}{G}^{\text{⚬}}$ is the transfer Gibbs energy and $\nu$ is the number of ions in the solute.