A comprehensive thermodynamic study of 9,10-dihydrophenanthrene

Abstract

The heat capacity of 9,10-dihydrophenanthrene was studied from 11 to 350 K by adiabatic calorimetry. The enthalpy of fusion is 12.79 kJ mol −1 at the triple-point temperature 306.520 K. The enthalpies of combustion of both the solid and the supercooled liquid were measured at 298.15 K. A value for the standard enthalpy of formation, ΔH f o(298.15 K), of (66.3 1 ± 1.2 2) kJ mol −1 was obtained for the solid and (78.5 0 ± 1.1 6) kJ mol −1 for the supercooled liquid. The enthalpy of vaporization for the supercooled liquid at 298.15 K was obtained from vapor-pressure measurements made in the range 353 to 418 K. This was combined with the enthalpy of formation of the supercooled liquid to derive the enthalpy of formation of the ideal gas at 298.15 K, (155.1 ± 1.6) kJ mol −1. Another value of ΔH f o(298.15 K) for the ideal gas was derived from the value for the solid by use of values of { H s ( T) − H o(0)} for the liquid and solid; this value of ΔH f o(298.15 K) is 155.4 kJ mol −1. Both differ significantly from the value of ΔH f o(298.15 K), (174.9 ± 8) kJ mol −1, estimated by Shaw, Golden, and Benson. Chemical thermodynamic properties for the ideal gas in the range 298.15 to 350 K were calculated.