The standard enthalpy of formation of (XeF5)2[MnF6](cr)

The enthalpies of interaction of (XeF₅)₂[MnF₆](cr) with a 0.0524 m solution of KOH and a 0.0300 m solution of H₂SO₄, the enthalpy of solution of KMnO₄(cr) in a 0.0440 m solution of KOH, and the enthalpy of mixing of aqueous KF with alkaline KMnO₄ were measured in isothermic-shell calorimeters at 298.15 K. The standard enthalpy of formation of the compound at 298.15 K was calculated by two independent procedures using the experimental values and literature data (Δ_f H ^o = −1185 ± 18 kJ/mol). Original Russian Text ? S.N. Solov’yov, A.A. Firer, A.Ya. Dupal, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 4, pp. 798–800.     

Standard enthalpy of formation of (NO2)2[NiF6](cr)

The enthalpies of interactions of (NO₂)₂[NiF₆](cr) with water and aqueous KOH, enthalpies of solution of KF(cr) in dilute aqueous solutions of KNO₃ and KOH, and enthalpy of mixing of solutions of NiF₂, HNO₃, and HF were measured at 298.15 K using isothermic-shell calorimeters. Based on the obtained data and values in the literature, the standard enthalpy of formation of the compound under study was determined by two independent methods: Δ_f H°(NO₂)₂[NiF₆](cr) = −1099 ± 9 kJ/mol.     

Zur Bestimmung der Bildungsenthalpie von SeCl4 und SeOCl2

Determination of the Enthalpies of Formation of SeCl₄ and SeOCl₂ The enthalpies of formation were derived for SeCl₄ and SeOCl₂ from the enthalpy of solution in NaOH. The determination is based on the enthalpy of formation for SeO₂, NaCl, and NaOH as well as on their enthalpy of solution. Results see ?Inhaltsübersicht”?.     

Thermochemische Untersuchung zur Stabilität von Orthosilicaten und -germanaten

Thermochemical Investigation on the Stability of Orthosilicates and -germanates The enthalpy of formation of Ca₂SiO₄, Sr₂SiO₄, Ba₂SiO₄, Cd₂SiO₄, Ca₂GeO₄, Sr₂GeO₄, Ba₂GeO₄, and Cd₂GeO₄ from the component oxides has been measured by solution calorimetry in a molten oxide solvent at 967 K, and, when possible, the values have been compared with data from the literature. All the thermochemical information (enthaply of formation, free enthalpy of formation, standard entropy and heat capacity) of the orthosilicates and -germanates of the alkali earths, the transition metals in the fourth period and cadmium have been collected and critically assessed. The reliable values of the enthalpy of formation and the entropy of formation as well as the free enthalpy of formation as a function of the temperature have been tabulated. On the basis of the existing thermochemical data regularities in the stability behaviour of the double oxides are discussed. The causes for stability differences and the reasons for the existence of the compounds in different structures are noted.     

Determination de l'enthalpie de formation du pentafluorotellurate iv de potassium KTeF5 par calorimetrie de reaction

The standard enthalpy of formation of KTeF₅ has been determined by reaction in a normal solution of KOH: ΔH°₂₉₈ KTeF₅ = ? 1687.37 ± 4,84 kJ.mol^?1     

Determination de l'enthalpie de formation du pentalfluorotellurate IV de rubidium RbTeF5 par calorimetrie de reaction

The standard enthalpy of formation of RbTeF₅ has been determined by hydrolysis reaction in a molar aqueous solution of NaOH or KOH as ΔH°₂₉₈f RbTeF_{5 cr} = ?1696 ± 1 kJ.mol^?1     

Energetics of formation of alkali and ammonium cobalt and zinc phosphate frameworks

Alkali and ammonium cobalt and zinc phosphates show extensive polymorphism. Thermal behavior, relative stabilities, and enthalpies of formation of KCoPO₄, RbCoPO₄, NH₄CoPO₄, and NH₄ZnPO₄ polymorphs are studied by differential scanning calorimetry, high-temperature oxide melt solution calorimetry, and acid solution calorimetry.α-KCoPO₄ and γ-KCoPO₄ are very similar in enthalpy. γ-KCoPO₄ slowly transforms to α-KCoPO₄ near 673 K. The high-temperature phase, β-KCoPO₄, is 5-7 kJ mol⁻¹ higher in enthalpy than α-KCoPO₄ and γ-KCoPO₄. HEX phases of NH₄CoPO₄ and NH₄ZnPO₄ are about 3 kJ mol⁻¹ lower in enthalpy than the corresponding ABW phases. There is a strong relationship between enthalpy of formation from oxides and acid-base interaction for cobalt and zinc phosphates and also for aluminosilicates with related frameworks. Cobalt and zinc phosphates exhibit similar trends in enthalpies of formation from oxides as aluminosilicates, but their enthalpies of formation from oxides are more exothermic because of their stronger acid-base interactions. Enthalpies of formation from ammonia and oxides of NH₄CoPO₄ and NH₄ZnPO₄ are similar, reflecting the similar basicity of CoO and ZnO.     

The calorimetric investigation of phosphoric acid-N,N-dimethylformamide system

Solution and mixing enthalpies for the orthophosphoric acid (H₃PO₄)-N,N-dimethylformamide (DMF) system were measured over the whole concentration range at 25 °C. The standard value of solution enthalpy of phosphoric acid in DMF and the standard transference enthalpy of H₃PO₄ from water to DMF were calculated. The mixing enthalpy concentration dependence permitted making assumptions on complex formation in the system under investigation.     

Zur calorimetrischen Bestimmung der Bildungsenthalpie von SeBr4 und SeOBr2

Calorimetric Determination of the Enthalpy of Formation of SeBr₄ and SeOBr₂ It was determined the enthalpy of solution of SeO₂, SeBr₄, and SeOBr₂ in 1 N HBr and derived the enthalpies of formation. The following data basing on the enthalpy of formation for SeO₂ were obtained .     

Thermodynamic properties of lanthanum molybdates

The enthalpy of solution of LаОНMoO₄ and Cs₂MoO₄ in aqueous HCl at 298 К has been determined by solution calorimetry, and the standard enthalpy of formation of lanthanum hydroxomolybdate has been calculated. The enthalpies of solution of NaLa(MoO₄)₂ and Na₅Lа(MoO₄)₄ in molybdate melt at 973 K have been determined by high-temperature melt solution microcalorimetry, and the high-temperature enthalpies of the double molybdates in the 298–1000 K range have been measured by the mixing method. The standard enthalpies of formation of the double molybdates have been calculated using data available from the literature. The low-temperature heat capacity of NaLa(MoO₄)₂ in the 60–300 K range has been measured on an adiabatic vacuum calorimeter. The basic thermodynamic properties of NaLa(MoO₄)₂, Na₅Lа(MoO₄)₄, and LаОНMoO₄ have been calculated.     

Thermochemical properties of dinitramidic acid salts

Enthalpies of formation and solution of hydrazinium, guanidinium, aminoguanidinium, and triaminoguanidinium salts of nitric and dinitramidic (HN(NO₂)₂, DN) acids were determined by combustion and solution calorimetry methods. Enthalpies of formation of respective cations in infinitely dilute aqueous solution were calculated using the enthalpy of formation of the nitrate ion. The enthalpy of formation of the DN acid anion was determined based on the enthalpy of formation and solution of the acid salts. The weight-average enthalpy of formation of the DN acid anion equal to 8.40±0.13 kcal mol⁻¹ was obtained. The enthalpy of solution of ammonium dinitramide (ADN) was measured (8.71±0.01 kcal mol⁻¹). From these data, the enthalpy of formation of ADN was calculated (−32.14±0.14 kcal mol⁻¹). The energy of combustion of ADN was measured by the calorimetry method, and the enthalpy of formation of ADN was calculated for a sample with purity above 99.9% (−32.20±0.19 kcal mol⁻¹). The weight-average enthalpy of formation of ADN equal to −32.16±0.11 kcal mol⁻¹ is recommended for use. Enthalpies of formation of sodium, potassium, and cesium salts of DN acid were determined.     

The enthalpy of formation of tungsten azide pentafluoride

The enthalpy of hydrolysis of solid tungsten azide pentafluoride in alkaline aqueous solution (1.O mol dm^?3 KOH; 298.2K) is ?578 kJ mol^?1. Hence its enthalpy of formation is ?1170 kJ mol^?1.     

Kinetics of reduction of hydroxycuprate(III) in KOH solution

The solution of an unstable copper(III) complex, hydroxycuprate(III) i.e. Cu(OH)^– ₄, has been obtained by oxidising a copper anode in 0.5–3 M KOH solution. The kinetics of the copper(III) reduction in KOH solution has been studied spectrophotometrically and is first order with respect to copper(III), and the pseudo-first order rate constant increases as the KOH concentration increases. The kinetic data is explained by a scheme according to which a Cu^III intermediate, in equilibrium with Cu(OH)^– ₄, reacts with OH^–. On the basis of the kinetic data, the molar absorptivity of the Cu(OH)^– ₄ solution has been determined.     

Energetics of cobalt phosphate frameworks: α, β, and red NaCoPO4

Thermal behavior, relative stability, and enthalpy of formation of α (pink phase), β (blue phase), and red NaCoPO₄ are studied by differential scanning calorimetry, X-ray diffraction, and high-temperature oxide melt drop solution calorimetry. Red NaCoPO₄ with cobalt in trigonal bipyramidal coordination is metastable, irreversibly changing to α NaCoPO₄ at 827 K with an enthalpy of phase transition of −17.4±6.9 kJ mol⁻¹. α NaCoPO₄ with cobalt in octahedral coordination is the most stable phase at room temperature. It undergoes a reversible phase transition to the β phase (cobalt in tetrahedra) at 1006 K with an enthalpy of phase transition of 17.6±1.3 kJ mol⁻¹. Enthalpy of formation from oxides of α, β, and red NaCoPO₄ are −349.7±2.3, −332.1±2.5, and −332.3±7.2 kJ mol⁻¹; standard enthalpy of formation of α, β, and red NaCoPO₄ are −1547.5±2.7, −1529.9±2.8, and −1530.0±7.3 kJ mol⁻¹, respectively. The more exothermic enthalpy of formation from oxides of β NaCoPO₄ compared to a structurally related aluminosilicate, NaAlSiO₄ nepheline, results from the stronger acid-base interaction of oxides in β NaCoPO₄ (Na₂O, CoO, P₂O₅) than in NaAlSiO₄ nepheline (Na₂O, Al₂O₃, SiO₂).     

Thermodynamic properties of normal and deuterated cyclopropenes

The specific heat, entropy, enthalpy, and Gibbs free energy of cyclopropene-d₀, cyclopropene-1-d₁, cyclopropene-3-d₁, cyclopropene-1,2-d₂, cyclopropene-3,3-d₂, cyclopropene-1,3,3-d₃, and cyclopropene-d₄ have been calculated for the temperature range 100–1500 K using the rigid-rotor and harmonic oscillator model. The standard enthalpy and Gibbs free energy of formation of cyclopropene-d₀ have also been evaluated for the same temperature range using the experimental standard enthalpy of formation at 298.15 K.     

Thermodynamics of CoAl2O4-CoGa2O4 solid solutions

CoAl₂O₄, CoGa₂O₄, and their solid solution Co(Ga_zAl_1−z)₂O₄ have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B₂O₃ at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing.     

Thermochemistry of iron manganese oxide spinels

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (Mn_xFe_1−x)₃O₄ at 298 K from the oxides, tetragonal Mn₃O₄ (hausmannite) and cubic Fe₃O₄ (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.67<x<1.0. Relative to cubic Mn₃O₄ (stable at high temperature) and cubic Fe₃O₄ (magnetite), the enthalpy of formation is negative for all compositions. The enthalpy of formation is most negative near x=0.2. There is no significant difference in the trend of enthalpy of formation versus composition for cubic (x<0.6) and tetragonal (x>0.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation-reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ΔS_mix, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4.     

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.     

The standard enthalpies of formation of cyclohexylamine and cyclohexylamine hydrochloride

The standard enthalpy of combustion of cyclohexylamine has been measured in an aneroid rotating-bomb calorimeter. The value ΔH_o^o(c-C₆H₁₁NH₂, 1) = ?(4071.3 ± 1.3) kJ mol^?1 yields the standard enthalpy of formation ΔH_f^o(c-C₆H₁₁NH₂, 1) = ?(147.7 ± 1.3) kJ mol^?1. The corresponding gas-phase standard enthalpy of formation for cyclohexylamine is ΔH_f^o(c-C₆H₁₁NH₂, g) = ?(104.9 ± 1.3) kJ mol^?1. The standard enthalpy of formation of cyclohexylamine hydrochloride, ΔH_f^o(c-C₆H₁₁NH₂·HCl, c) = ?(408.2 ± 1.5) kJ mol^?1, was derived by combining the measured enthalpy of solution of the salt in water, literature data, and the ΔH_c^o measured in this study. Comment is made on the thermochemical bond enthalpy H(CN).     

The standard molar enthalpy of formation of LnPO4(s) (Ln = La, Nd, Sm) by solution calorimetry

The standard molar enthalpy of formation of LaPO₄(s), NdPO₄(s), and SmPO₄(s) has been determined using an isoperibol solution calorimeter. The solution calorimeter vessel was held at 298.15 K. The precipitation reaction between aqueous solution of rare-earth chloride (LnCl₃(aq.)) and ammoniacal solution of ammonium dihydrogen phosphate (NH₄H₂PO₄(aq.)) was studied. The temperature of the calorimeter vessel was measured before, during, and after the reaction. The enthalpy change due to precipitation of LaPO₄(s), NdPO₄(s), or SmPO₄(s) from required solutions was measured at 298.15 K. Using these values and other auxiliary data from the literature, thermochemical reaction scheme were devised to calculate the standard enthalpy of formation of each phosphate compound i.e., LaPO₄(s), NdPO₄(s), and SmPO₄(s). The calculated values for LaPO₄(s), NdPO₄(s), and SmPO₄(s) at 298.15 K were found to be ?1947.5 ± 3.2, ?1938.3 ± 3.6, and ?1942.9 ± 3.4 kJ mol^?1, respectively.