2ND VIRIAL-COEFFICIENTS OF BENZENE AND CYCLOHEXANE FROM MEASUREMENTS OF THE EXCESS MOLAR ENTHALPY OF (0.5N(2)+0.5C(6)H(6)) AND (0.5N(2)+0.5C(6)H(12)) FROM 333.2 K TO 433.2 K

Values of the second virial coefficient B of benzene and cyclohexane h ave been obtained from measurements of the excess molar enthalpy H-m(E ) of {yN(2) + (1 - y)C6H6} and {yN(2) + (1 - y)C6H12} measured at stan dard atmospheric pressure over the temperature range 333.2 to 433.2 K. In a hypothetical mixture of an ideal gas with benzene or cyclohexane a measurement of H-m(E) is equivalent to a measurement of the isother mal Joule-Thomson coefficient phi 22 of the hydrocarbon. In a mixture of the nearly ideal gas nitrogen with hydrocarbon, phi(11) for nitroge n is small. The cross term isothermal Joule-Thomson coefficient phi(12 ) is also small and can be calculated with adequate accuracy using an established combining rule. Potential parameters which fit B-22 and ph i(22) for the hydrocarbon can then be calculated from the H-m(E) measu rements. It is shown that the H-m(E) measurements yield values of phi( 22) for benzene and cyclohexane which are in good agreement with value s obtained from throttling experiments, and that values of B-22 agree well with those obtained from (p, rho(n), T). It is suggested that H-m (E) measurements on these mixtures might be useful for testing the per formance of mixing calorimeters, and empirical equations which fit the measurements at mole fraction y = 0.5 are given. (C) 1996 Academic Pr ess Limited