Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C 14H 12O)

Abstract

Low-temperature heat capacities of the 9-fluorenemethanol (C 14H 12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be T fus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Δ fus H m=(26.273±0.013) kJ · mol −1 and Δ fus S m=(69.770±0.035) J · K −1 · mol −1. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Δ c U(C 14H 12O, s)=−(7125.56 ± 4.62) kJ · mol −1 and Δ c H m ∘(C 14H 12O, s)=−(7131.76 ± 4.62) kJ · mol −1, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, Δ f H m ∘(C 14H 12O,s)=−(92.36 ± 0.97) kJ · mol −1, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.