BENZENE-DIMETHYL KETONE ASSOCIATION - EXCESS MOLAR ENTHALPY OF (CYCLOHEXANE PLUS DIMETHYL KETONE)(G) AND (BENZENE PLUS DIMETHYL KETONE)(G) FROM TEMPERATURES OF 353.2 TO 403.2 K

A differential flow mixing calorimeter has been used to measure the ex cess molar enthalpy H-m(E) of (cyclohexane + dimethyl ketone(g) and (b enzene + dimethyl ketone)(g) at standard atmospheric pressure over the temperature range 353.2-403.2 K. The non-ideality of the cyclohexane and benzene was fitted using the Kihara potential, and that of the dim ethyl ketone using the Stockmayer potential. Cross terms were calculat ed using the equation epsilon(12) = (1 - k(12))(E11E22)(1/2) and to fi t the measurements on (cyclohexane + dimethyl ketone)(g) the value (1 - k(12)) = 1.175 was needed. None of the usual combining rules give th is value. The measurements on (benzene + dimethyl ketone)(g) could not be fitted by adjusting the value of (1 - k(12)), though an approximat e fit could be obtained using the value 1.38. The difference between t he experimental values of HEm for (benzene + dimethyl ketone)(g) and t hose calculated using (1 - k(12)) = 1.175, the value appropriate to (c yclohexane + dimethyl ketone)(g), was described in terms of a quasi-ch emical model, which, for the benzene-dimethyl ketone interaction, yiel ded a value of the equilibrium constant K-12(298.15 K) = 0.349 MPa-1 a nd an enthalpy of association Delta H-12 = -(16.4 +/- 2) kJ mol(-1). T his value of Delta H is attributed to a charge transfer interaction be tween the benzene and dimethyl ketone molecules which is not present i n the cyclohexane-dimethyl ketone interaction.