Fluorine bomb calorimetry. Part 18.—Standard enthalpy of formation of phosphorus pen afluoride and enthalpies of transition between various forms of phosphorus. Thermodynamic functions of phosphorus pentafluoride between 0 and 1500°K
Abstract
The energies of combustion in fluorine of α-white phosphorus and three modifications of red phosphorus—amorphous I, crystalline IV and crystalline V—were measured. With the adoption of α-white phosphorus as standard state, the standard enthalpy of formation of PF5(g) at 25° was calculated to be –380.8±0.3 kcal mole–1. The enthalpies of transition at 25° for the following processes are reported: P(α-white)→P(amorphous red I), ΔHt=–3.9±0.4 kcal g-atom–1; P(α-white)→P(red V), ΔHt=–3.9±1.5 kcal g-atom–1; P(red IV)→P(red V), ΔHt=–1.2±1.0 kcal g-atom–1. High-temperature thermodynamic functions for PF5(g) are also reported.
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