where 𝑅 $ is the universal gas constant, and 𝑇 is the temperature. Eq. 13 is entirely dependent on molar concentration, and not affected by the specific physical properties of the solute or solvent, so long as the condition of membrane semi-permeability is met. For mixed-solvent systems, however, the Van't Hoff equation loses accuracy if the solvent species exhibit non-ideal mixing behaviour towards the solute and each other (𝛾 , ≠ 1). In this case, in the spirit of its thermodynamic definition for a single-solvent system, 𝛥𝛱 may be identified by considering the pressure difference 𝛥𝑃 , for which the mechanical energy produced by reversible transfer of a volume 𝑉 balances the concurrent change in the chemical free energy. When the volume V includes Ni moles of solvent species 𝑖 transferred across the membrane, we obtain a free energy balance: