transfer activity coefficient, γ t

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 $Δ t G ° = ν R T ln γ t$ where $Δ t G °$ is the transfer Gibbs energy and $ν$ is the number of ions in the solute.

Notes:

It should not be confused with the mass transfer coefficient which represents the specific rate of transfer of a species from one phase to another.
It does not necessarily imply the physical transfer of a solute between two liquid phases.