Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

The vapor pressures of three 4-substituted acetanilide derivatives (namely, 4-ethoxyacetanilide, 4- hydroxyacetanilide and 4-bromoacetanilide) were measured above their liquids using the mass loss rates determined by thermogravimetry under both isothermal and nonisothermal diffusion-controlled conditions. The coefficient used to convert mass loss rates in vapor pressures showed a slight increase with increasing temperature. Therefore, the small deviations observed from the mean value enable the use of a single calibration value to be considered reasonable. From the temperature dependence of the vapor pressure estimated using a calibration constant for each technique the molar enthalpies of vaporization g l H. m( T ) were determined, respectively, at the middle T of the respective temperature intervals. The melting temperatures and the molar enthalpies of fusion of these compounds were measured by differential scanning calorimetry. Finally, the standard molar enthalpies of sublimation g crH. m(298.15 K) were obtained at the reference temperature of 298.15K using the standard molar enthalpies of vaporization g l H. m( T ), the molar enthalpies of fusion, the heat capacity differences between gas and liquid and the heat capacity differences between gas and solid, g l C. p,m and g crC. p,m, respectively, both estimated by applying a group additivity procedure. Therefore, the averages of the standard (p. = 0.1MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15 K, have been derived: