EXCESS MOLAR ENTHALPIES OF ETHANOL HEXANE, ETHANOL CYCLOHEXANE AND ETHANOL BENZENE FROM 453.5 TO 522.9 K AND UP TO 4.5 MPA

Flow calorimetric measurements of the excess molar enthalpy, H(m)E, of [0.5C2H5OH + 0.5C6H14](g), [0.5C2H5OH + 0.5C6H12](g) and [0.5C2H,OH 0.5C6H6](g) are reported. The measurements extend over the temperatur e range 453.5 to 522.9 K and are at pressures up to 4.5 MPa. Residual molar enthalpies of hexane, cyclohexane and benzene were calculated fr om the equation of state proposed by Kubic, and the residual molar ent halpy of ethanol was calculated from a modification of Kubic's equatio n proposed by Massucci and Wormald. For ethanol in its interaction wit h hexane or cyclohexane there is no hydrogen bonding, and the excess m olar enthalpy can be fitted by applying simple one-fluid mixing rules using a pseudo-critical temperature of 345 K and a pseudocritical pres sure of 4.65 MPa for ethanol. For ethanol-benzene the values of H(m)E calculated by this method are too large. Previous measurements of H(m) E for benzene with steam or methanol showed similar behaviour, and the difference between the experimental values of H(m)E and those calcula ted from an equation of state was attributed to association between th e steam or methanol and the benzene molecules. Using a similar approac h we attributed the difference between the experimental and calculated values of H(m)E for ethanol-benzene to weak association between the u nlike molecules, and obtained a value of the equilibrium constant K12 (298.15 K) = 0.2197 MPa-1 and a value of DELTAH12 = -14.0 kJ mol-1 for the enthalpy of the specific interaction between ethanol and benzene.