Thermodynamics Research Center / ThermoML | Thermochimica Acta

ABSTRACT

The vapor pressures above the solid hexachlorobenzene (HCB) and above both the solid and liquid 1,2,3,4,5,6-hexachlorocyclohexane (lindane) were determined in the ranges 332-450 K and 347-429 K, respectively, by measuring the mass loss rates recorded by thermogravimetry under both isothermal and non-isothermal conditions. The results obtained were compared with those taken from literature. From the temperature dependence of vapor pressure derived by the experimental thermogravimetry data the molar enthalpies of sublimation 'cr g HmcentsX(less thanTgreater than) were selected for HCB and lindane as well as the molar enthalpy of vaporization 'l g HmcentsX(less thanTgreater than) for lindane only, at the middle less thanTgreater than of the respective temperature intervals. The melting temperatures and the molar enthalpies of fusion 'cr l HmcentsX(Tfus) of lindane were measured by differential scanning calorimetry. Finally, the standard molar enthalpies of sublimation 'cr g HmcentsX(298.15 K) were obtained for both chlorinated compounds at the reference temperature of 298.15 K using the 'cr g HmcentsX(less thanTgreater than), 'l g HmcentsX(less thanTgreater than) and 'cr l HmcentsX(Tfus) values, as well as the heat capacity differences between gas and liquid and the heat capacity differences between gas and solid, 'l g Cp,mcentsX and 'cr g Cp,mcentsX, respectively, both estimated by applying a group additivity procedure. Therefore, the averages of the standard (pcentsX=0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15 K, have been derived: