A Thermodynamic Test for the Internal Consistency of Experimental Data on Volatility Ratios

Abstract

An important measurable parameter in the study of vapour-liquid equilibria in two-phase binary mixtures is the volatility ratio (α) defined by N₁^g.N₂/N₁.N₂^g, where N₁^g is the mol fraction of component 1 in the vapour and N₂ that of component 2, while N₁ and N₂ are the corresponding quantities for the liquid. In view of the difficulties inherent in the determination of α, the need for a thermodynamic test of the reliability of experimental data has been expressed¹. In this note such a test will be described and also a method given for deriving δG^E from the curve of α plotted against N₁ where δG^E is the excess 4 free energy of formation of the mixture over an ideal mixture of the same composition. A study of this quantity (δG^E) is fundamental to the investigation of the structure of liquid mixtures.