where µ 0 i (T ; P 0 ) is the species ideal-gas (IG) chemical potential at T and reference state pressure P 0 = 1 bar, P is expressed in bar, and ρ solv is the density of the pure solvent. (ρ solv denotes its expression in kg m -3 ). µ † i (T, P ) is numerically equal to the species chemical potential in a hypothetical ideal solution of unit molality.