BENZENE-CHLOROFORM ASSOCIATION - EXCESS MOLAR ENTHALPY OF (CYCLOHEXANE PLUS CHLOROFORM)(G) AND (BENZENE PLUS CHLOROFORM)(G) AT TEMPERATURESFROM 353.2 TO 423.2 K

A flow-mixing calorimeter has been used to measure the excess molar en thalpy H-m(E) of (cyclohexane + chloroform)(g) and (benzene + chlorofo rm)(g) at standard atmospheric pressure over the temperature range 353 .2-423.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the chloroform using the Stoc kmayer potential. Cross-terms were calculated using the equation epsil on(1/2) = (1-k(12))(epsilon(11)epsilon(12))(1/2) and to fit the measur ements on (cyclohexane + chloroform)(g) the value (1-k(12)) = 0.965 wa s needed. This value was used to calculate H-m(E) for (benzene + chlor oform)(g), and the calculated values were found to be positive and to be similar to those for (cyclohexane + chloroform)(g). However, the ex perimental values are negative, and about 35 J mol(-1) below the value s for (cyclohexane + chloroform)(g). The difference between the calcul ated and experimental values was described in terms of a quasichemical model that, for the benzene-chloroform interaction, yielded a value o f the equilibrium constant K-12(298.15 K) = 0.373 MPa-1 and an enthalp y of association Delta H-12 = -(16.1 +/- 2) kJ mol(-1). This value of Delta H-12 is attributed to a charge transfer between the benzene and the chloroform that is not present in the cyclohexane-chloroform inter action.