Quantitative interpretation of excess properties of n-alkane mixtures through Prigogine's solution theory

Abstract

A refinement of Prigogine's corresponding states theory for chain-molecule mixtures is presented. Explicit analytical expressions are derived for the excess free energy (g^E), activity coefficient (γ_A), excess enthalpy (h^E) and excess volume (ν^E), and the resulting equations applied to n-alkane mixtures. The proposed approach contains parameters that are physically realistic and in essential agreement with those determined purely through corresponding states arguments. The method employs only one adjustable parameter, the number of external degrees of freedom per segment (3c/r), which is determined empirically from available g.l.c. solute activity coefficients at infinite dilution (γ^∞ _A). The theoretical treatment leads to the following agreement with the observed excess properties of n-alkane mixtures (average difference between calculated and observed values quoted): γ^∞ _A(±0.006)γ_A(+0.010), equimolar h^E(±14 J mol^–1) and equimolar ν^E(±0.03 cm³ mol^–1). Also, the observed sign reversal in h^E at elevated temperatures is correctly predicted.