THERMODYNAMICS OF THE LANTHANIDE TRIFLUORIDES. II. THE HEAT CAPACITY OF PRASEODYMIUM TRIFLUORIDE PRF3 FROM 5 TO 350°K

The heat capacity of a well‐characterized sample of NdF3 was measured by aneroid adiabatic calorimetry from 5 to 350 ° K. The following results were determined at 298.15 ° K: the heat capacity, Cp= (92.42±0.09) J ° K−1 mole−1; the entropy, S°= (120.79±0.12) J °K−1 mole−1; the enthalpy increment, [H °  (298.15 °K)−H°  (0)]=17 360±17 J mole−1; and the Planck function, −[G° (298.15° K)−H ° (0)]/T= (62.56±0.06) J ° K−1 mole−1. The values of the last three functions were adjusted for the removal of the degeneracy associated with the ground‐state Kramer’s doublet of Nd+3. A table of recommended thermal functions of NdF3 from 400 to the melting temperature, 1650 °K is presented. The excess heat capacity due to the internal electronic energy levels of Nd+3 was calculated from spectroscopic data and also from calorimetric results and the two calculations were found to be in reasonable agreement.