Thermodynamic properties of binary mixtures of hexane isomer and cyclohexane at 298.15 K

Excess molar enthalpies HmE and excess molar volumes VmE at 298.15 K are reported for binary mixtures of hexane isomer (1-hexane (Hx), 2-methylpentane (2MP), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB), 2,2-dimethylbutane (22DMB)) + cyclohexane (CH). The results of excess molar enthalpies are endothermic in the whole concentration for all the mixtures. On the other hand, the results of excess molar volumes are positive for Hx system, and are negative for 23DMB and 22DMB systems and change positive to negative with increase of the mole fraction of hexane isomer x for 2MP and 3MP systems. The values of HmE (x=0.5) of hexane isomer + cyclohexane mixtures are large in order HX>2MP>3MP>23DMB>22DMB. This order is reverse to those of decalin isomer+hexane isomer mixtures reported in our group previously [Fluid Phase Equilib. 46 (1989) 59]. These results were explained by using Flory theory and from solvation enthalpy of one component in the other component. The values of VmE (x=0.5) for these mixtures tend from positive values to negative one in the same order as HmE except for 2MP and 3MP. The results of VmE for these mixtures are explained by the differences of the free volume and the geometric packing between the component molecules. The solvation enthalpies of the component liquid are correlated to the excess partial molar volumes of the component liquid at infinite dilution.