BENZENE-DICHLOROMETHANE ASSOCIATION - THE EXCESS MOLAR ENTHALPY OF (CYCLOHEXANE PLUS DICHLOROMETHANE)(G) AND (BENZENE PLUS DICHLOROMETHANE)(G) FROM THE TEMPERATURE 353.2 K TO 453.2

A flow-mixing calorimeter has been used to measure the excess molar en thalpy H-m(E) of (cyclohexane + dichloromethane)(g) and (benzene + dic hloromethane)(g) at standard atmospheric pressure over the temperature range (353.2 to 453.2) K. The non-ideality of the cyclohexane and ben zene was fitted using the Kihara potential, and that of the dichlorome thane using the Stockmayer potential. Cross-terms were calculated usin g the equation epsilon(12) = (1 - k(12))(epsilon(11)epsilon(22))(1/2), and to fit the measurements on (cyclohexane + dichloromethane)(g) the value (1 - k(12)) = 1.005 was needed. This value was used to calculat e H-m(E) for (benzene + dichloromethane)(g), and the calculated values were found to be positive and about as large as those for (cyclohexan e + dichloromethane)(g). However the experimental values are negative, and at T = 353.2 K are about 50 J.mol(-1) below the values for (cyclo hexane + dichloromethane)(g). The difference between the calculated an d experimental values was described in terms of a quasi-chemical model which, for the benzene-dichloromethane interaction, yielded a value o f the equilibrium constant K-12 (298.15 K) = 0.323 MPa-1 and an enthal py of association Delta H-12 = -(12.8 +/- 3) kJ.mol(-1) This value of Delta H-12 is attributed to charge transfer between benzene and dichlo romethane which is not present in the cyclohexane-dichloromethane inte raction. (C) 1998 Academic Press.