Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following 4-n-alkylbenzoic acids: 4-methylbenzoic acid, between 319.68 K and 337.33 K, 4-ethylbenzoic acid, between 321.17 K and 335.25 K, 4-propylbenzoic acid, between 331.16 K and 347.16 K, 4-butylbenzoic acid, between 333.16 K and 349.15 K, 4-pentylbenzoic acid, between 341.16 K and 357.16 K, 4-hexylbenzoic acid, between 347.08 K and 363.14 K, 4-heptylbenzoic acid, between 353.16 K and 369.20 K and 4-octylbenzoic acid, between 356.67 K and 371.86 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard, po=105 Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T=298.15 K, were derived. A d.s.c. study of the crystalline polymorphic transitions, fusion and isotropization of liquid crystals is also presented.