Issue 16, 2002

Sulfur dioxide–benzene association. Second virial cross coefficients for sulfur dioxide–benzene and sulfur dioxide–cyclohexane derived from gas phase excess enthalpy measurements

Abstract

A flow mixing calorimeter has been used to measure the excess molar enthalpy HEm of gaseous (sulfur dioxide + benzene) and (sulfur dioxide + cyclohexane) at the mole fraction y = 0.5, at standard atmospheric pressure, and over the temperature range 363.15 K to 473.15 K. The measurements were analysed in terms of the virial equation of state. The cross coefficient B12 was calculated using the arithmetic mean rule for collision diameters and the rule ε12 = (1 − k12)(ε11ε22)1/2 for the depth of the potential well. The HEm measurements on (sulfur dioxide + cyclohexane) were fitted to within experimental error by the choice (1 − k12) = 1.01 but this value did not fit the measurements on (sulfur dioxide + benzene). The difference was attributed to a specific interaction which was analysed in terms of a quasi-chemical association model in which B12 = Bns12 − (RTK12)/2. The non-specific term Bns12 was calculated using (1 − k12) = 1.01, and values of the equilibrium constant K12 were determined from the difference between the calculated and experimental excess enthalpies. A plot of ln K12 against reciprocal temperature yielded an enthalpy of formation ΔH12 of the sulfur dioxidebenzene complex and this was found to be −(8.7 ± 2) kJ mol−1. The sum of the specific and non-specific contributions is −(13.8 ± 3) kJ mol−1. As this energy is an average taken over all orientations it should be less than the binding energy of the van der Waals complex in the minimum energy configuration computed by ab initio methods. Taleb-Bendiab et al. (A. Taleb-Bendiab, K. W. Hillig and R. L. Kuczkowski, J. Chem. Phys., 1992, 97, 2996) computed an ab initio value of −12 kJ mol−1, which is smaller than our value. Grover et al. (J. R. Grover, E. A. Walters, J. K. Newman and M. G. White, J. Am. Chem. Soc, 1985, 107, 7329) used photoionisation spectroscopy and obtained −(16.7 ± 0.8) kJ mol−1, which is in better agreement.

Article information

Article type
Paper
Submitted
07 Feb 2002
Accepted
17 May 2002
First published
09 Jul 2002

Phys. Chem. Chem. Phys., 2002,4, 4008-4013

Sulfur dioxidebenzene association. Second virial cross coefficients for sulfur dioxidebenzene and sulfur dioxidecyclohexane derived from gas phase excess enthalpy measurements

C. J. Wormald, Phys. Chem. Chem. Phys., 2002, 4, 4008 DOI: 10.1039/B201404C

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