A New Condensed Gas Calorimeter. Thermodynamic Properties of Solid and Liquid Dinitrogen Oxide

Abstract

Abstract A new adiabatic calorimeter for use with condensed gases from 1.8 K to room temperature has been constructed. The heat capacity of solid and liquid dinitrogen oxide was measured between 1.9 and 184 K together with the vapor pressure above 146 K. The residual entropy was re-evaluated as 6.0 J K−1 mol−1, which is now closer to R ln2, suggesting that the disorder of molecular end-for-end orientation is perfectly frozen in the solid state. The moments of lattice frequency spectrum were derived from low-temperature heat capacities and hightemperature vapor pressures. The anomalous increase of heat capacity below the triple point was interpreted as arising from thermal creation of orientational defects with the enthalpy of formation 10.8 kJ mol−1. Other thermodynamic quantities determined are as follows: triple point of pure N2O 182.407±0.002 K, heat of fusion 6516±20 J mol−1, entropy of fusion 35.7±0.1 J K−1 mol−1, heat of vaporization at 184.81 K and 101.7 kPa 16544±20 J mol−1, normal boiling point 184.74 K, translational zero-point energy 1.6±0.3 kJ mol−1, Debye temperature corresponding to 3N degrees of freedom 141.0±1.0 K.