Karl A. Gingerich

Gaseous Metal Nitrides. II. The Dissociation Energy, Heat of Sublimation, and Heat of Formation of Zirconium Mononitride

The ZrN molecule has been identified in the vapor phase over a ZrN–BN mixture at temperatures above 2400°K using a combination of effusion and mass spectrometric techniques. Its apprearance potential was measured as 7.9 ± 0.4 eV. From the experimentally determined partial pressures the equilibrium constants and the enthalpy for the gaseous reaction ZrN = Zr + 0.5 N2 have been calculated. The reaction enthalpy was obtained as ΔH°298 = 22.0 ± 5.0 kcal/mole. Combined with published thermodynamic data this reaction enthalpy yields the following thermodynamic properties for gaseous ZrN: ZrN(g) = Zr(g) + N(g) D°298 = 135.0 ± 6.0 kcal ZrN(s) = ZrN(g) ΔH°s, 289 = 211.4 ± 9.0 kcal Zr(s) + 0.5N2(g) = ZrN(g) ΔH°f, 298 = 123.5 ± 7.0 kcal.

Vaporization of Uranium Mononitride and Heat of Sublimation of Uranium

The vaporization of uranium mononitride UN has been investigated by the Knudsen effusion technique in combination with a mass spectrometer. The vaporization occurs incongruently by preferential loss of nitrogen forming the two‐phase system nitrogen‐saturated liquid uranium–uranium‐saturated nonstoichiometric uranium mononitride. The vapor pressures of U and N2 have been obtained by silver calibration over the two‐phase system UN0.4–UN0.9 in the temperature range 1910–2230°K. The enthalpies ΔH°298 for the simplified reaction (1) UN(s)=U(g)+0.5 N2 (g) and its partial reactions (2) UN(s)=U(l)+0.5 N2(g) and (3) U(l)=U(g) have been obtained from second‐ and third‐law treatments. The experimental third‐law value of Partial Reaction (3) of 130.7 ± 2.2 kcal mole−1 may be considered an upper value for the heat of vaporization of uranium metal. The third‐law enthalpy of Partial Reaction (2) of 68.9 ± 0.4 kcal mole−1 is in general agreement with literature data for this reaction. The selected value for the enthalpy ...

Gaseous Metal Nitrides. III. On the Dissociation Energy of Thorium Mononitride and Predicted Dissociation Energies of Diatomic Group III–VI Transition‐Metal Nitrides

Mass‐spectrometric evidence for the existence of gaseous thorium mononitride over a nitrogen‐containing thorium–boron–phosphorus alloy has been obtained. The enthalpies ΔH°298 of the reactions ThN(g) = Th(g) + 0.5N2(g) and ThP(g) + 0.5N2(g) = ThN(g) + 0.5P2(g) have been calculated from the experimentally determined partial pressures of the reactants as 23.1 ± 6.0 and 7.0 ± 5.0 kcal/mole. Combined with published thermodynamic data these reaction enthalpies yield the respective dissociation energy D°298, the heat of formation, ΔH°f,298, and the heat of sublimation, ΔH°s,298 of 138.0 ± 8, 112.5 ± 7.5, and 203.1 ± 10 kcal/mole for gaseous ThN. The dissociation energies of the diatomic nitrides of the Group III–VI transition metals have been estimated on the basis of empirical correlations by Colin and Goldfinger and by Pauling. The values, which range from 96 kcal/mole for CrN to 145 kcal/mole for TaN, are explained in terms of a strong ionic contribution to the bonding. On the basis of the calculated dissoci...

Gaseous phosphorus compounds: Part V. The dissociation energy and heat of formation of carbon monophosphide☆

Abstract The chemical equilibrium CP(g) + P(g) ⇌ P 2 (g) + C(g) has been studied by means of the Knudsen effusion technique combined with mass spectrometric analysis of the vapor. The enthalpy of reaction, Δ H O 298− was determined as 6.3 ± 4.0 kcal/mole. Combined with the literature value for the dissociation energy of P 2 , the dissociation energy of gaseous carbon monophosphide was calculated as D O 298 = 123.2 ± 4.0 kcal/mole or D O O = 122.1 ± 4.0 kcal/mole. The corresponding value for the standard heat of formation is ΔH O f.298 = 127.5±4.5 kcal/mole. This compares with the selected JANAF value of 111.7 ± 23.1 kcal/mole.