Thermodynamic properties of fluorine compounds. Part VII. Heat capacity and entropy of pentafluorochlorobenzene and pentafluorophenol

Abstract

The heat capacities of pure samples of pentafluorochlorobenzene and pentafluorophenol have been measured in the condensed states over the temperature range 12–394°K. The heat of vaporization of pentafluorochlorobenzene in the pressure range ¼–1 atm. and the vapour heat capacity between 383 and 498°K have been determined. Both compounds undergo thermal transitions in the crystalline state. Heats of transition and melting were measured, and thermodynamic properties of crystals and liquid were computed. The entropies at 298·15°K of C₆F₅Cl (I) and C₆F₅OH (c) were found to be 300·7 and 227·1 J deg.^–1 mole^–1 respectively. Possible molecular changes associated with the thermal transitions in the solid are discussed. A value of 407·6 J deg.^–1 mole^–1 was found for the entropy of C₆F₅Cl in the ideal-gas state (at 298·15°K and 1 atm. pressure).