Abstract
Thermodynamic properties were determined for bismuth trifluoride that had been dried by heating in a stream of hydrogen fluoride. The melting point was found to be 649° C. The thermodynamic functions of the gaseous molecule were calculated from estimates of the molecular geometry and vibration frequencies. Heat capacities were measured for the solid and liquid, and the heat (5.16 kcal) and entropy of fusion (5.6 eu) were obtained.
The vapor pressure over the solid was measured by a transpiration method. The vapor pressure of 
over the solid is given by
An equation for the vapor pressure over the liquid was derived and the boiling point calculated to be 900°C. The enthalpy of sublimation (48.1 kcal/mole) and the entropy of sublimation (46.6 eu) at 298°K were derived from the vapor pressures.
The enthalpy of formation of bismuth trifluoride (−215 kcal/mole) was determined by solution calorimetry. The enthalpy of atomization of bismuth trifluoride gas (273 kcal/mole) was calculated from the enthalpy of formation. The derived bismuth‐fluorine bond energy is compared with those of the other group VA halides.