Determination of Gibbs free energy of formation of Cr3P by double Knudsen cell mass spectrometry

The vapor pressure of phosphorus in equilibrium with a mixture of elemental Cr and Cr3P at (1523 to 1623) K was estimated by double Knudsen cell mass spectrometry with a Cu–P alloy as a reference substance. The Gibbs free energy of formation of Cr3P was calculated from the vapor pressure as follows:3Cr(s) + 1/2P2(g) = Cr3P(s)ΔfG∘=-261,000+83.0(T/K)±6800J·mol-1(1523