Construction of an adiabatic calorimeter in the temperature range between 13 and 505 K, and thermodynamic study of 1-chloroadamantane

Abstract

An adiabatic calorimeter working in the temperature range between 13 and SOS K was constructed. The calorimeter was designed so as to minimize the temperature drift in each adiabatic shield and to achieve highly stable temperature around the calorimeter cell. The imprecision in the thermometry was found to be 10 −5 K. The imprecision in the heat capacity measurement was found to be less than ± 0.04%, and the inaccuracy to be less than ± 0.4% between 13 and 50 K and less than ± 0.2% above 50 K, respectively. Heat capacities of 1-chloroadamantane were measured between 13 and 445 K with this calorimeter, and the standard thermodynamic functions were evaluated. The temperature, enthalpy, and entropy of fusion were determined to be (439.7 ± 0.1) K, (5.53 ± 0.01) kJ mol −1 and (12.6 ± 0.1) J K −1 mol −1, respectively. The temperature and enthalpy of crystalline phase transition were determined to be (248.6 ± 0.1) K and (4.30 ± 0.02) kJ mol −1, respectively, and the corresponding entropy was (17.3 ± 0.1) J K −1 mol −1. The magnitude of entropy is discussed in connection with the restricted disorder of molecular orientations in the plastically crystalline phase. Heat capacity anomaly of a kind of Schottky type was observed around 310 K in the plastically crystalline phase, and its potential molecular mechanism is considered.