Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. IX. Bildungsenthalpie und Sättigungsdruck des MoOBr3

From the enthalpy of solution of MoOBr₃ in NaOH/H₂O₂ the enthalpy of formation ΔH°(MoOBr₃,f,298) = ?109,5(±0,4) kcal/mol was derived. The sublimation of MoOBr₃ is connected with simultaneous decomposition (see “Inhaltsübersicht”). From the temperature function of the saturated vapor pressure the values ΔH°(subl., MoOBr₃, 298) = 36(±1,5) kcal/mol and ΔS°(subl., MoOBr₃, 298) = 56(±3) cl are calculated.     

Sättigungsdrucke,Bildungsenthalpien von WOBr4 und WO2Br2, die Reaktionsgleichgewichte 2WO2Br2 = WO3 + WOBr4 und 2WOBr4 + SiO2 = 2WO2Br2 + SiBr4

The saturation vapour pressures of WOBr₄ and WO₂Br₂ and their reaction equilibria have been determined by means of a membrane zero manometer and ampoule quenching experiments, respectively. From the pressuretemperature dependence the following sublimation data were estimated: Δ H° (subl., WOBr₄, 298) = 29.4 (± 1.0) kcal/mole; Δ H° (subl., WO₂Br₂, 298) = 36.6 (±1.5) kcal/mole; Δ S° (subl., WOBr₄, 298) = 50.1 (± 1) cl; Δ S° (subl. WO₂Br₂, 298) = 53.0 (±1.5) cl. For the decomposition reaction of solid WO₂Br₂ were obtained: Δ H° (s, 690) 37.5 (± 0.7) kcal/mole, Δ S° (s, 690) = 49.0 (± 0.5) cl; and for the decomposition of gaseous WO₂Br₂: Δ H° (g, 690) = ?29.6 (± 2.0) kcal/mole, Δ S°. (g, 690) = ?44.5 (± 1.5) cl.     

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram,VIII. WOBr3, WOBr2-Bildungsenthalpie und thermische Zersetzung

WOBr₃ and WOBr₂ were prepared by chemical transport reactions. From the solution enthalpy of WOBr₃ in NaOH/H₂O₂ the formation enthalpy ΔH°(WOBr₃,f,298) = ?113,2(±0,9) kcal/Mol was calculated. The thermal decomposition of WOBr₃ proceeds primarly according to 2 WOBr₃ = WOBr₂ + WOBr₄. The decomposition of WOBr₂ may be described by the reaction 2 WOBr₂ = WBr₂ + WO₂Br₂. The interpretation of the decomposition equilibrium of WOBr₃ gives the values ΔH°(WOBr₂,f,298) = ?116,9(±5) kcal/Mol, and S°(WOBr₃,f,298) = 46(±5) cl.     

Knudsen measurements of the sublimation and the heat of formation of GeSe2 [1]

Knudsen effusion studies of the sublimation of polycrystalline GeSe₂ have been performed employing mass spectrometry in a temperature range of about 610–750 K and vacuum microbalance techniques in the temperature range 614–801 K and at pressures ranging from about 10^?7 ? 10^?4 atm. The results demonstrate that GeSe₂ vaporizes congruently under present experimental conditions according to the predominant reaction (1) GeSe₂(s) = GeSe(g) + 1/2 Se₂(g) and a minor reaction (2) GeSe₂(s) = GeSe₂(g). The mean values for the third law heat and second law entropy of reaction (1) based on direct mass-loss data are ΔH°₂₉₈ = 70.4 ± 2 kcal/mole and ΔS°₂₉₈ = 64.7 ± 2 eu. From these the standard heat of formation and absolute entropy of GeSe₂(s) were calculated to be ?21.7 ± 2 kcal/mole and 24.6 ± 2 eu, respectively.     

Das Dimerisierungsgleichgewicht 2 TiCl3,g = Ti2Cl6,g

The Dimerization Equilibrium 2 TiCl_3,g = Ti₂Cl_6,g The dimerization of gaseous titanium(III)chloride has been investigated. The measurement have been made in the presence of an excess of TiCl₄ by means of a static method using gold as a manometer liquid. The results for the equilibrium 2 TiCl_3,g = Ti₂Cl_6,g are ΔH°(298) = ?40.6 kcal; ΔS°(298) = ?36.4 cl; ΔCp = 4 cal/°, mole.     

Equilibrium sublimation and thermodynamic properties of SnSe and SnSe2

Knudsen effusion studies of the sublimation of polycrystalline SnSe and SnSe₂, prepared by annealing and chemical vapor transport reactions, respectively, have been carried out using vacuum microbalance techniques in the temperature ranges 736–967 K and 608–760 K, respectively. From experimental mass-loss data for the sublimation reaction SnSe(s) = SnSe(g), the recommended values for the heat of formation and absolute entropy of SnSe(s) were calculated to be ΔH°_298,f = ?86.4 ± 9.9 kJ · mol^?1 and S°₂₉₈ = 89.0 ± 7.1 J · K^?1 · mol^?1. From mass-loss data for the decomposition reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SnSe}_{\rm 2} ({\rm s)} = {\rm SnSe(s)} + \frac{1}{{\rm x}}{\rm Se}_{\rm x} ({\rm g) (x} = 2 - 8) $\end{document}, the recommended values for the heat of formation and absolute entropy of SnSe₂(s) were determined to be ΔH°_298,f = ?118.1 ± 15.1 kJ · mol^?1 and S°₂₉₈ = 111.8 ± 11.8 J · K^?1 mol^?1.     

The very low-pressure pyrolysis of phenyl methyl sulfide and benzyl methyl sulfide. The enthalpy of formation of the methylthio and phenylthio radicals

The kinetics and mechanisms of the unimolecular decompositions of phenyl methyl sulfide (PhSCH₃) and benzyl methyl sulfide (PhCH₂SCH₃) have been studied at very low pressures (VLPP). Both reactions essentially proceed by simple carbon-sulfur bond fission into the stabilized phenylthio (PhS·) and benzyl (PhCH₂·) radicals, respectively. The bond dissociation energies BDE(PhS-CH₃) = 67.5 ± 2.0 kcal/mol and BDE(PhCH₂-SCH₃) = 59.4 ± 2 kcal/mol, and the enthalpies of formation of the phenylthio and methylthio radicals ΔH° _,298K(PhS·, g) = 56.8 ± 2.0 kcal/mol and ΔH°_{f, 298K}(CH₃S·, g) = 34.2 ± 2.0 kcal/mol have been derived from the kinetic data, and the results are compared with earlier work on the same systems. The present values reveal that the stabilization energy of the phenylthio radical (9.6 kcal/mol) is considerably smaller than that observed for the related benzyl (13.2 kcal/mol) and phenoxy (17.5 kcal/mol) radicals.     

Die Gasmolekeln Pd2Al2Cl10 und PdAlCl5 als Begleiter von PdAl2Cl8

Gas Molecules Pd₂Al₂Cl₁₀ and PdAlCl₅ as Accompanists of PdAl₂Cl₈ Mass spectrometric observations using a double cell showed that the reaction of gaseous Al₂Cl₆ with solid PdCl₂ besides the known gaseous complex PdAl₂Cl₈ gives PdAlCl₅ and the unexpected complex Pd₂Al₂Cl₁₀. For the equilibrium (with ΔCp? ?1 cal/K) ΔH°(298) = 7.5 kcal/Mol and ΔS°(298) = 5.3 ± 2 cl have been obtained.     

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. IV. Der Transport von MoO2 mit J2 und die Existenz von MoO2J2

The possibility to transport MoO₂ with J₂ in a temperature gradient T₂/T₁ suggests the existence of MoO₂J₂. Starting from the reaction MoO₂ + J₂ ? MoO₂J₂ in the consideration of the function of temperature for the rates of chemical transport, the values ΔH^O_R ? 28.8 (±2) kcal/mole and ΔS^O_R ? 9.0 (±2) cl are deduced. From this the values ΔH^O(MoO₂J₂, g, 298) ? ?99.5 (±3.5) kcal/mole and S^O(MoO₂J₂, g, 298) ? 86 (±3) cl are derived. The comparison of the thermodynamic data for MoO₂X₂ and WO₂X₂ (X = Cl, Br, J) leads to the conclusion, that the existence of MoO₂J₂ in the vapour phase is very probable indeed.     

ab initio calculations and thermochemical analysis on C1 atom abstractions of chlorine from chlorocarbons and the reverse alkyl abstractions: Cl2 + R· ↔ Cl· + RCl

Thermodynamic properties (ΔH°_f(298), S°₍₂₉₈₎ and Cp(T) from 300 to 1500 K) for reactants, adducts, transition states, and products in reactions of CH₃ and C₂H₅ with Cl₂ are calculated using CBSQ//MP2/6‐311G(d,p). Molecular structures and vibration frequencies are determined at the MP2/6‐311G(d,p), with single‐point calculations for energy at QCISD(T)/6‐311 + G(d,p), MP4(SDQ)/CbsB4, and MP2/CBSB3 levels of calculation with scaled vibration frequencies. Contributions of rotational frequencies for S°₍₂₉₈₎ and Cp(T)'s are calculated based on rotational barrier heights and moments of inertia using the method of Pitzer and Gwinn [1]. Thermodynamic parameters, ΔH°_f(298), S°₍₂₉₈₎, and C_P(T), are evaluated for C₁ and C₂ chlorocarbon molecules and radicals. These thermodynamic properties are used in evaluation and comparison of Cl₂ + R· → Cl· + RCl (defined forward direction) reaction rate constants from the kinetics literature for comparison with the calculations. Data from some 20 reactions in the literature show linearity on a plot of Ea_fwd vs. ΔH_rxn,fwd, yielding a slope of (0.38 ± 0.04) and intercept of (10.12 ± 0.81) kcal/mole. A correlation of average Arrhenius preexponential factor for Cl· + RCl → Cl₂ + R· (reverse rxn) of (4.44 ± 1.58) × 10¹³ cm³/mol‐sec on a per‐chlorine basis is obtained with Ea_Rev = (0.64 ± 0.04) × ΔH_rxn,Rev + (9.72 ± 0.83) kcal/mole, where Ea_Rev is 0.0 if ΔH_rxn,Rev is more than 15.2 kcal/mole exothermic. Kinetic evaluations of literature data are also performed for classes of reactions. Ea_fwd = (0.39 ± 0.11) × ΔH_rxn,fwd + (10.49 ± 2.21) kcal/mole and average A_fwd = (5.89 ± 2.48) × 10¹² cm³/mole‐sec for hydrocarbons: Ea_fwd = (0.40 ± 0.07) × ΔH_rxn,fwd + (10.32 ± 1.31) kcal/mole and average A_fwd = (6.89 ± 2.15) × 10¹¹ cm³/mole‐sec for C₁ chlorocarbons: Ea_fwd = (0.33 ± 0.08) × ΔH_rxn,fwd + (9.46 ± 1.35) kcal/mole and average A_fwd = (4.64 ± 2.10) × 10¹¹ cm³/mole‐sec for C₂ chlorocarbons. Calculation results on the methyl and ethyl reactions with Cl₂ show agreement with the experimental data after an adjustment of +2.3 kcal/mole is made in the calculated negative Ea's. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 548–565, 2000     

Very-low-pressure pyrolysis of N-methyl aniline and N,N-dimethyl aniline. Enthalpy of formation of the anilino and N-methyl anilino radicals

The kinetics of the thermal unimolecular decompositions of N-methyl aniline and N,N-dimethyl aniline into anilino and N-methyl anilino radicals, respectively, have been studied under very low-pressure conditions. The enthalpies of formation of both radicals, ΔH°_f,298°K(Ph?H,g) = 55.1 and ΔH°_f,298°K(Ph?Me,g) = 53.2 kcal/mol, which have been derived from the experimental data, lead to BDE(PhNH-H) = 86.4 ± 2, BDE[PhN(Me)-H] = 84.9 ± 2 kcal/mol and to a value of 16.4 kcal/mol for the stabilization energy of the PhNH radical (relative to MeNH). These results are discussed in connection with earlier work. At high temperatures, the anilino radical loses HNC and forms the very stable cyclopentadienyl radical, a decomposition comparable to that of the phenoxy radical.     

Die Störung durch kleine Wassergehalte bei der Messung der Dissoziationsenthalpie von Ga2Cl6 = 2 GaCl3

Disturbance by Small Water Contents during the Measurement of the Dissociation Enthalpy of Ga₂Cl₆ = 2 GaCl₃ Small water contents are difficult to exclude before the dissociation of Ga₂Cl₆ is studied. Taking into account the small amount of HCl, which arises from that, the values ΔH°(298) = 22.49 kcal and ΔS°(298) = 35.95 cal/K are obtained using ΔCp = ?4 cal/K we got for Ga₂Cl_6,g = 2 GaCl_3,g.     

Untersuchungen der Zersetzungsgleichgewichte und zur Phasenbreite der Molybdäntelluride

Investigation of Decomposition Equilibria and the Phase Fields of Molybdenum Tellurides The Te₂-pressure over Mo₃Te₄ and MoTe₂ as well as over equilibrium mixtures of Mo+Mo₃Te₄, Mo₃Te₄+MoTe₂, and MoTe₂+Te.l, respectively, has been measured directly between 1100 and 1373 K. No remarkable deviations from stoichiometry exist for MoTe₂ as well as for Mo₃Te₄. The coexistence pressures are for Mo/Mo₃Te₄: lg p/10⁵ Pa = 5.56—9879/T, and for Mo₃Te₄/MoTe₂: lg p/10⁵ Pa = 8.398—11790 /T. Third law enthalpies are derived: Δ_fH°(298, Mo₃Te₄) = —195.5±10 with S°(298) = 268, and Δ_fH°(298, αMoTe₂) = —89.5 ± 11 with S°(298) = 115.3 (values in kJ/mol and J mol^?1 K^?1, respectively).     

Beiträge zur Chemie der Oxid-halogenide von Molybdän und Wolfram. VII. Thermische Zersetzung und Bildungsenthalpie von WOCl3 und WOCl2

The thermal decomposition of WOCI₃ proceeds in the first decomposition step according to 2 WOCl₃,s = WOCl₂,s + WOCl₄,g. The second decomposition step of WOCI₃ is identical with the thermal decomposition of WOCI₂, equation see “Inhaltsübersicht” The interpretation of the decomposition equilibrium of WOCl₃ gives the heat of formation: ΔH°(WOCl₂,s,298) = ?155(±4) kcal/Mol. The heat of formation δH° (WOCl₃,s,298) = ?174,15(±0,8) kcal/Mol was determined from the solution enthalpy of WOCl₃ in 2n NaOH with 1% H₂O₂.     

Thermische Zersetzung und Lösungskalorimetrie von Ammoniumsamariumbromiden

Thermal Decomposition and Solution Calorimetry of Ammonium Samarium Bromides The ternary pure phases on the line SmBr₃—NH₄Br in the thermodynamically equilibrium have been synthesized by solid state reactions and characterized by X‐ray powderdiffraction. The existence of a new phase (NH₄)₃SmBr₆ was demonstrated beside the known phases (NH₄)₂SmBr₅ and NH₄Sm₂Br₇. The decomposition equilibria of the ammonium samarium bromides have been investigated by total pressure measurements and the thermodynamical data of the solid phase complexes derived from the decompostion functions. The standard enthalpies of solution in 4n HBr (aq.) of the ternary phases, SmBr₃ and Sm₂O₃, were measured and on the basis of these values and known data the standard enthalpies of ammonium samarium bromides were derived. The phase diagram is constructed on the basis of DTA measurements. Data from total pressure measurements: ΔH((NH₄)₃SmBr_{6, f, 298}) = —400, 0 ± 6, 5 kcal/mol S°((NH₄)₃SmBr_{6, f, 298}) = 146, 9 ± 8 cal/K · mol ΔH((NH₄)₂SmBr_{5, f, 298}) = —340, 6 ± 5, 0 kcal/mol S°((NH₄)₂SmBr_{5, f, 298}) = 106, 0 ± 6 cal/K · mol Δ(NH₄Sm₂Br_{7, f, 298}) = —479, 4 ± 6, 0 kcal/mol S°(NH₄Sm₂Br_{7, f, 298}) = 119, 5 ± 7 cal/K · mol Data from solution calorimetry: ΔH(SmBr_{3, f, 298}) = —204, 4 ± 1, 8 kcal/mol ΔH((NH₄)₃SmBr_{6, f, 298}) = —400, 7 ± 3, 2 kcal/mol ΔH((NH₄)₂SmBr_{5, f, 298}) = —339, 6 ± 2, 6 kcal/mol ΔH(NH₄Sm₂Br_{7, f, 298}) = —475, 6 ± 4, 4 kcal/mol     

The kinetics and equilibrium of the gas-phase reaction CH3CF2Br + I2 = CH3CF2I + IBr the C-Br bond dissociation energy in 1,1-difluorobromoethane

The kinetics and equilibrium of the gas-phase reaction of CH₃CF₂Br with I₂ were studied spectrophotometrically from 581 to 662°K and determined to be consistent with the following mechanism: A least squares analysis of the kinetic data taken in the initial stages of reaction resulted in log k₁ (M^?1 · sec^?1) = (11.0 ± 0.3) - (27.7 ± 0.8)/θ where θ = 2.303 RT kcal/mol. The error represents one standard deviation. The equilibrium data were subjected to a “third-law” analysis using entropies and heat capacities estimated from group additivity to derive ΔH_r° (623°K) = 10.3 ± 0.2 kcal/mol and ΔH_rr (298°K) = 10.2 ± 0.2 kcal/mol. The enthalpy change at 298°K was combined with relevant bond dissociation energies to yield DH°(CH₃CF₂ - Br) = 68.6 ± 1 kcal/mol which is in excellent agreement with the kinetic data assuming that E₂ = 0 ± 1 kcal/mol, namely; DH°(CH₃CF₂ - Br) = 68.6 ± 1.3 kcal/mol. These data also lead to ΔH_f°(CH₃CF₂Br, g, 298°K) = -119.7 ± 1.5 kcal/mol.     

Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potential

DyI₂ and Dy_3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be Δ_fH°(DyI₂, s, 298 K) = ?(394 ± 16) kJ· mol^?1 and Δ_fH°(DyI₃, s, 298 K) = ?(616 ± 10) kJ· mol^?1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy³⁺/Dy²⁺, aq) was calculated to be ?(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI₃ to DyI₂ and of DyCl₃ to DyCl₂.     

Der chemische Transport von FeP2 und FeP4 mit lod

Chemical Transport of FeP₂ and FeP₄ with Iodine Experiments on the chemical transport of FeP₂ and FeP₄ with iodine are discussed, considering the gaseous molecules I₁, I₂, FeI₂, Fe₂I₄, FeI₃, Fe₂I₆, PI₃, P₂I₄, P₄, P₂, and P. Thermodynamic calculations give δH°(298) = 56.322 kcal and ΔS°(298) = 39.5 cal/K for the reaction FeP_2,f + I₂ = FeI₂ + 0.5 P₄ and δG°(923) = 35.8 kcal for the reaction FeP_4,f + I₂ = FeI₂ + P₄.     

The fluorobasicities of ReF7 and IF7 as measured by the enthalpy change ΔH°(EF7(g) → EF6+(g) + F−(g))

Iridium hexafluoride oxidizes ReF₆ (via an ReF₆⁺ salt) and at room temperatures IrF₆, ReF₆, ReF₇ and (IrF₅)₄ are each present in the equilibrium mixture. From these and related findings: ΔH°(ReF₆ → ReF₆⁺ + e^?) 1092 ± 27 kj mole^?1(261 ± 6 kcal mole^?1), and thermodynamic data are selected to yield ΔH°(ReF_7(g) → ReF₆⁺_(g) + F^?_(g))=893 ± 33 kj mole^?1(213 ± 8 kcal mole^?1). From observations on the stability of IF₆⁺BF₄^? and the lattice enthalpy evaluation for the salt, ΔH°(IF_7(g) → IF₆⁺_(g) + F^?_(g))= 870 ± 24 kj mole^?1(208 ± 6 kcal mole^?1).     

Spectra and thermodynamics of the cobalt(II) chloride — aluminum chloride gaseous complexes

The reaction of solid cobalt(II) chloride with gaseous aluminum chloride to form blue gaseous complex(es) has been studied spectrophotometrically, in the range 600–800 K and 1–3 atm. The data are rationalized in terms of the reaction: CoCl₂(s) + Al₂Cl₆(g) → CoAl₂Cl₈(g) (ΔH° = 10.0 ± 0.2 Kcal/mole, ΔS° = 9.8 ± 0.3 e.u.). The electronic absorption spectrum of the gaseous complex was compared with the spectra of Co(II) in different molten salt solvents. Thermodynamic and spectroscopic considerations suggest that the predominant absorbing species in the gaseous phase are Co(AlCl₄)₂ molecules having the Co(II) in a close to octahedral coordination.