Thermodynamic study of the sublimation of six halobenzoic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following halobenzoic acids: 2-chlorobenzoic acid, between T = (320.16 and 339.15) K, 3-chlorobenzoic acid, between T = (320.13 and 340.13) K, 4-chlorobenzoic acid, between T = (333.15 and 356.14) K, 2-bromobenzoic acid, between T = (327.56 and 347.68) K, 3-bromobenzoic acid, between T = (327.67 and 347.60) K and 4-bromobenzoic acid, between T = (348.67 and 366.65) K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard, p∘ = 105 Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K, were derived. A d.s.c. study of the fusion of the crystals is also presented.