Enthalpy of sublimation of benzoic acid and dimerization in the vapor phase in the temperature range from 320 to 370 K

Abstract The enthalpy of sublimation has been determined for benzoic acid as a function of temperature in the temperature range from 320 to 370 K by use of a sublimation-calorimetric system incorporating a Calvet microcalorimeter. From analysis of the effect of the (monomer + dimer) equilibria in the vapor on the observed enthalpies of sublimation, the degree of dissociation of the dimer in the saturated vapor at 298.15 K has been estimated to be higher than 0.997. The enthalpy of sublimation to give the gaseous monomer at 298.15 K is in the range from (88.9 ± 0.3) to (89.3 ± 0.3) kJ · mol −1 .