medium effect

https://doi.org/10.1351/goldbook.M03815
The medium effect on ionic species B due to transfer from solvent S1 to solvent S2 (number) is defined by R T lnγS1S2(B)=μBo,S2μBo,S1 where R is the gas constant, T is the thermodynamic temperature and μBo,Si is the standard chemical potential of B in solvent Si (where i = 1 or 2), the reference states being the same in both solvents. γS1S2(B) is not an exactly measurable quantity.
Source:
PAC, 1974, 37, 499. (Electrochemical nomenclature) on page 508 [Terms] [Paper]