Vapor pressures, standard molar enthalpies, entropies Gibbs energies of sublimation and heat capacities of 2,5- and 3,5-dibromobenzoic acids

Abstract

The vapor pressures of solid and liquid 2,5- and 3,5-dibromobenzoic acids were determined by torsion–effusion and thermogravimetry (under both isothermal and non-isothermal conditions), respectively. The molar enthalpies of sublimation ΔcrgHm°(Tm) and vaporization ΔlgHm°(Tm) were calculated, respectively, at the middle temperature (Tm) of the respective temperature intervals from the temperature dependence of vapor pressure derived by the experimental torsion–effusion and thermogravimetric data. The melting temperatures and the molar enthalpies of fusion of these compounds were determined by d.s.c. as well as the molar heat capacities (in the temperature range from 288.2K to 326.2K). The molar enthalpies and entropies of sublimation and vaporization obtained by torsion–effusion and thermogravimetry, respectively, were adjusted to the reference temperature of 298.15K using the estimated heat capacity differences between gas and liquid for vaporization experiments and the estimated heat capacity differences between gas and solid for sublimation experiments. Therefore, the averages of the standard (p°=0.1MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15K, have been derived:CompoundΔcrgHm°(298.15K) (kJ/mol)ΔcrgSm°(298.15K) (J/(molK))ΔcrgGm°(298.15K), kJ/mol2,5-Dibromobenzoic acid (cr)133.0±3.0263.6±8.054.4±5.03,5-Dibromobenzoic acid (cr)120.4±3.0209.1±8.058.0±5.0