Second virial coefficient of methanol from measurements of the excess molar enthalpy of methanol–nitrogen

Abstract

Flow calorimetric measurements of the excess molar enthalpy, H^E_m, of [xCH₃OH–(1 –x)N₂]_g are reported. The measurements extend over the range 338.2–423.2 K at pressures from 53.8 to 99.8 kPa. These are analysed in terms of an assocciation model involving dimer, trimer and tetramer equilibria. Dispersion and dipolar forces were estimated by using fluoromethane as a homomorph for methanol. Cross-term virial coefficients were small, and could be adequately estimated on this basis. As preliminary calculations showed that the measurements could be fitted by assuming only dimer and tetramer equilibria, this model was adopted. The dimer–tetramer model was found to fit literature values of the isobaric heat capacity measured at several temperatures and pressures. Second virial coefficients derived from the analysis are in good agreement with previous work at temperatures above 400 K, and are less negative at lower temperatures.