Excess properties, g[superscript E] and v[superscript E] six binary liquid mixtures at 25°C of six normal and isomeric alkanes (C₅ and C₆) and of perfluorobenzene and toluene

Abstract

The density measurements and total vapor pressure measurements as a function of com position were carried out at 25°C for six liquid mixtures of non-electrolytes, including n-hexane + n-pentane, n-hexane + 2-methylpentane, n-hexane + 3-methylpentane, n-hexane + 2,2-dimethylbutane, n-hexane + 2,3, - dimethylbutane, and hexafluorobenzene + toluene. The molar excess volumes v[superscript E] were found to be negative and small for the alkane systems and positive and slightly larger for the fluorinated aromatic + aromatic hydrocarbon system. The molar excess E Gibbs energies g[superscript E] for the six systems at 25°C were calculated from the isothermal data on total vapor pressures and liquid compositions according to Barker's method. The values of g[superscript E] are positive for n-hexane + 2-methylpentane and n-hexane + 3-methylpentane, but negative for the other four systems. The objective of this study w as to investigate the contribution of a methyl group in different chemical environments to the excess properties. The analysis revealed that the isomeric variation procedure may be applied to v[superscript E] but not to g[superscript E]. It appears from the experimental results that the donor-acceptor interaction in the system hexafluorobenzene + toluene dominates, particularly in the hexafluorobenzene-rich region, and may be due to formation of complexes. The experimental results are discussed in the light of the current theories of solutions due to Hildebrand-Scott, Flory et al., and Prigogine.