Excluded volume contribution to deviations from ideality in liquid mixtures: Consequences for engineering models

The contribution from volume exclusion to departures from ideality in binary liquid mixtures is assessed in the case of mixtures of noble gases (Ar+KrAr+Kr and Kr+XeKr+Xe), and of ‘simple’, i.e. symmetric-top, molecules (chloromethane+fluoromethanechloromethane+fluoromethane: CH3Cl+CH3FCH3Cl+CH3F and trichloromethane (chloroform) + acetonitrile: CHCl3+CH3CNCHCl3+CH3CN). In the first case, this is done by estimating the equivalent hard sphere diameter of the atoms. In the second case, a description of the liquid mixtures is developed within the Padé approximation applied to dipolar–quadrupolar molecules. Excess chemical potentials and activity coefficients of the species in the mixture are determined using data for vapor–liquid equilibria. It is found that volume exclusion constitutes a large contribution to deviations from ideality in the mixtures studied.