The medium effect on ionic species B due to transfer from solvent \(\text{S}_{1}\) to solvent \(\text{S}_{2}\) (number) is defined by \[R\ T\ \ln \gamma _{\text{S}_{1}}^{\text{S}_{2}}\left(\text{B}\right)=\mu _{\text{B}}^{\text{o},\text{S}_{2}}- \mu _{\text{B}}^{\text{o},\text{S}_{1}}\] where \(R\) is the @G02579@, \(T\) is the @T06321@ and \(\mu _{\text{B}}^{\text{o},\text{S}_{i}}\) is the standard @C01032@ of B in solvent \(\text{S}_{i}\) (where \(i\) = 1 or 2), the reference states being the same in both solvents. \(\gamma _{\text{S}_{1}}^{\text{S}_{2}}(\text{B})\) is not an exactly @M03788@.