No abstract available

[en] Highlights: • Consistent enthalpies of formation and lattice energies of crystalline Pr₄N⁺ halides were selected. • The standard molar enthalpy of formation of gaseous Pr₄N⁺ ions was obtained. • The standard molar enthalpy of hydration of Pr₄N⁺ was estimated. - Abstract: The standard molar enthalpies of formation of crystalline tetraalkylammonium halides, Δ_fH°(R₄NX, c), R = Me, Et, Pr, Bu and X = Cl, Br, I, and the corresponding lattice energies, U_L(R₄NX) were obtained from the literature as far as available for T = 298.15 K. From consistent values of these two quantities and values for Δ_fH°(X⁻, g) the standard molar enthalpies of formation of the gaseous cations were obtained from Δ_fH°(R₄N⁺, g) = Δ_fH°(R₄NX, c) + U_L(R₄NX) + 2RT° − Δ_fH°(X⁻, g). The value for the hitherto unreported Δ_fH°(Pr₄N⁺, g) = (307 ± 7) kJ · mol is here derived. The value for the absolute standard molar enthalpy of hydration is Δ_hH°(R₄N⁺, aq) −210 kJ · mol⁻¹, but may have an appreciable uncertainty, reflecting that of Δ_fH°(R₄N⁺, aq), obtained from interpolation of values for the Me, Et, and Bu analogues

[en] Enthalpies of formation were determined by solution calorimetry for UO₂Br₂.H₂O, UO₂Br₂.3H₂O and UO₂(OH)Br.2H₂O. Enthalpy increments, Hdeg(T) - Hdeg(298.15K), were determined for UO₂F₂, UO₂Cl₂, and UO₂Br₂ by drop calorimetry

No abstract available

[en] Standard enthalpies of formation (Δ_f H⁰) of finite-length (5, 5) single-walled carbon nanotubes (SWNTs) are calculated with the framework of density functional theory. Approximate expressions of (Δ_f H⁰) have been proposed for both H-terminated and C30-capped (5, 5) SWNTs, based upon which the calculated values of (Δ_f H⁰) have been reproduced within several kilocalories per mole. It is also found that standard enthalpies of formation contributed by per carbon, Δ_f H⁰(C), oscillate with the increment of the cluster size, suggesting the dependence of the relative stability on the axial length.

[en] The standard enthalpy of formation of γ-UO₃ has been critically assessed; the value -(292.5 +- 0.2) kcalsub(th) mol^-1 is suggested. The enthalpies of solution of βUO₃ and γ-UO₃ in 3 M H₂SO₄ have been measured and used to derive: ΔHsub(f)sup(o)(β-UO₃, 298.15 K) = -(291.6 +- 0.2) kcalsub(th)mol^-1. (author)

No abstract available

[en] Highlights: • We calculate enthalpies of formation with the G2, G3, G4, and ccCA-PS3 methods. • Results for HMX and PETN represent the largest molecules attempted with these methods. • Mean absolute deviations from average experimental values are 12, 6, 7, and 3 kcal/mol. We report gas-phase enthalpies of formation for the set of energetic molecules NTO, DADE, LLM-105, TNT, RDX, TATB, HMX, and PETN using the G2, G3, G4, and ccCA-PS3 quantum composite methods. Calculations for HMX and PETN hitherto represent the largest molecules attempted with these methods. G3 and G4 calculations are typically close to one another, with a larger difference found between these methods and ccCA-PS3. Although there is significant uncertainty in experimental values, the mean absolute deviation between the average experimental value and calculations are 12, 6, 7, and 3 kcal/mol for G2, G3, G4, and ccCA-PS3, respectively.

[en] Highlights: • Standard enthalpies of formation of chlorine oxyfluorides were calculated. • Higher coupled cluster excitations were found to be important. • Isodesmic model of calculation was used in order to compensate errors. There is a lack of experimental thermochemical values for most chlorine oxyfluorides. Previous high level theoretical, CCSD(T), results showed uncommonly large errors in the standard heats of formation calculated through the atomization method. We propose that the differences are due to unusually large contributions to energy from higher excitations within the coupled cluster framework, and we tackle the problem by using a calculation scheme based on isodesmic reactions. Our suspicions are supported by results of static correlation diagnostics. Our final recommended values are in better agreement with the experimental data available. Other thermodynamic properties are also calculated.

No abstract available