Enthalpy of formation of wulfenite (natural lead molybdate)

A thermochemical study of wulfenite, i.e., natural lead molybdate PbMoO₄ (Kyzyl-Espe field deposit, Central Kazakhstan), is performed on a Setaram high-temperature heat-flux Tian-Calvet microcalorimeter (France). Enthalpies of the formation of wulfenite from oxides Δ_f H _ox ^o (298.15 K) = ?88.5 ± 4.3 kJ/mol and simple substances Δ_f H°(298.15 K) = ?1051.2 ± 4.3 kJ/mol were determined by means of melt calorimetry. The Δ_f G°(298.15 K) of wulfenite corresponding to ?949.1 ± 4.3 kJ/mol was calculated using data obtained earlier for S°(298.15 K) = 161.5 ± 0.27 J/(K mol).     

The enthalpies of formation of natural and synthetic nanotubular chrysotile

The thermochemical properties of natural chrysotile-asbestos and synthetic nanotubular chrysotile were studied on a high-temperature heat conducting Tian-Calvet microcalorimeter. The enthalpies of their formation from the elements at 298.15 K were determined by mélt solution calorimetry at 973 K. The Δ_f H _el ^° (298.15 K) value obtained for natural chrysotile-asbestos was close to that reported in the literature. The enthalpy of formation of synthetic nanotubular chrysotile was determined for the first time. The relation between the microstructural features of nanotubes and calorimetric data is discussed.     

The thermodynamic properties and thermal decomposition of octachlorotrisilane Si<Subscript>3</Subscript>Cl<Subscript>8</Subscript>

The standard enthalpies of formation of liquid and gaseous octachlorotrisilane were estimated, Δ_f H ^o (298.15, Si₃Cl₈, g) = ?1397(9) kJ/mol and Δ_f H ^o (298.15, Si₃Cl₈, l) = ?1447(9) kJ/mol. The decomposition of Si₃Cl₈ over the temperature range 400–1000 K was studied theoretically.     

The thermodynamic characteristics of vaporization of praseodymium triiodide

The vaporization of praseodymium triiodide was studied by high-temperature mass spectrometry. Monomeric (PrI₃) and dimeric (Pr₂I₆) molecules and the PrI ₄ ^? and Pr₂I ₇ ^? negative ions were recorded in saturated vapor over the temperature range 842–1048 K. The partial pressures of neutral vapor components were determined. The enthalpies of sublimation Δ_s H ^o(298.15 K) in the form of monomers (291 ± 10 kJ/mol) and dimers (400 ± 30 kJ/mol) were calculated by the second and third laws of thermodynamics. The equilibrium constants of ion-molecular reactions were measured and the enthalpies of the reactions determined. The enthalpies of formation Δ_f H ^o(298.15 K) of molecules and ions in the gas phase were calculated (?373 ± 11, ?929 ± 31, ?865 ± 25, and ?1433 ± 48 kJ/mol for PrI₃, Pr₂I₆, PrI ₄ ^? , and Pr₂I ₇ ^? , respectively).     

A calorimetric study of the thermodynamic properties of potassium molybdate

The low-temperature heat capacity of K₂MoO₄ was measured by adiabatic calorimetry. The smoothed heat capacity values, entropies, reduced Gibbs energies, and enthalpies were calculated over the temperature range 0–330 K. The standard thermodynamic functions determined at 298.15 K were C _p ^° (298.15 K) = 143.1 ± 0.2 J/(mol K), S°(298.15 K) = 199.3 ± 0.4 J/(mol K), H°(298.15 K)-H°(0) = 28.41 ± 0.03 kJ/mol, and Φ°(298.15 K) = 104.0 ± 0.4 J/(mol K). The thermal behavior of potassium molybdate at elevated temperatures was studied by differential scanning calorimetry. The parameters of polymorphic transitions and fusion of potassium molybdate were determined.     

Thermal decomposition of zinc and cadmium zirconyl oxalates

The enthalpy of formation at 298.15 K of the polymer Al₁₃O₄(OH)₂₈(H₂O)³⁺₈ and an amorphous aluminium trihydroxide gel was studied using an original differential calorimetric method, already developed for adsorption experiments, and aluminium-27 NMR spectroscopy data. ΔH_f “Al₁₃” (298.15 K) = ? 602 ± 60.2 kJ mole^?1 and ΔH_f Al(OH)₃ (298.15 K) = ? 51 ± 5 kJ mole^?1. Using theoretical values of ΔG_R “Al₁₃” and ΔG_R Al(OH)₃, we calculated ΔG_f “Al₁₃” (298.15 K) = ? 13282 kJ mole^?1; ΔS_f “Al₁₃” (298.15 K) = + 42.2 kJ mole^?1; ΔG_f Al(OH)₃ (298.15 K) = ? 782.5 kJ mole^?1; and ΔS_f Al(OH)₃ (298.15 K) = + 2.4 kJ mole^?1.     

Calorimetric determination of the enthalpy of formation of partheite,a calcium zeolite

A thermochemical study of partheite of composition (Ca_1.96Mg_0.04Na_0.01K_0.01) · [(Al_4.04Fe _0.01 ³⁺ )Si_3.95O_14.97(OH)_2.03] · 4.2H₂O, a natural calcium zeolite extracted from gabbro pegmatites of the Denezhkin Kamen’ deposit (North Ural, Russia), was performed. The enthalpies of formation of partheite from the constituent oxides, (Δ_f H°_ox(298.15 K) = ?359 ± 21), and elements, (Δ_f H°_el(298.15 K) = ?10108 ± 21), were determined by means of high-temperature in-melt-dissolution calorimetry. On the basis of the experimental data obtained, the enthalpy of formation of partheite of theoretical composition Ca₂[Al₄Si₄O₁₅(OH)₂] · 4H₂O from the elements was evaluated, ?10052 ± 21 kJ/mol.     

Thermodynamique de composes azotes. VII. Etude thermochimique du pyrazole et de l'imidazole

Enthalpies of sublimation for pyrazole and imidazole have been obtained by calorimetry at 298.15K. The ΔH⁰_sub (298.15 K) values for these two compounds are, respectively, 69.16 ± 0.32 and 74.50 ± 0.40 kJ mole^?1. From literature data obtained by combustion calorimetry for ΔH⁰_f (c, 298.15 K), the enthalpies of formation of these compounds in the gaseous state (pyrazole: 185.1 ± 2.3 kJ mole^?, imidazole: 133.0 ± 1.7 kJ mole^?1) have been derived. Several energy values related to the molecular structure of these two compounds (as resonance energy, enthalpy of isomerization, …) have been determined. The study of pyrazole has enabled us to contribute to the evaluation of some characteristics of the NN bond.     

Calorimetric studies of natural talc: Enthalpy of dehydroxylation

The standard dehydroxylation enthalpy of natural talc Mg₃[Si₄O₁₀](OH)₂ (87.8 ± 9.0 kJ/mol at 298.15 K) and the enthalpy of formation of dehydrated talc from the elements (Δ_f H _el^o (298.15 K) = −5527.0 ± 9.0 kJ/mol) were determined for the first time using Hess’s law, based on the total values of the enthalpy increments in heating a sample from room temperature to 973 K and the enthalpies of dissolution at 973 K for dehydrated talc measured in this work and those previously determined for talc and corresponding oxides.     

The enthalpy of formation of natural siderophyllite

A thermochemical study of lithium siderophyllite (K_0.75Na_0.06Rb_0.01Ca_0.11)(Li_0.11Fe _1.25 ²⁺ Mn_0.02Mg_0.66Al_0.35Fe _0.23 ³⁺ Ti_0.18)[Si_2.53Al_1.47O₁₀](OH)_1.63F_0.37 (I) and siderophyllite (Al-Fe biotite) (K_0.89Na_0.04)(Fe _1.69 ²⁺ Mn_0.03Mg_0.20Al_0.59Fe _0.14 ³⁺ Ti_0.06)[Si_2.80Al_1.20O₁₀](OH)_0.80F_1.16Cl_0.04(II) was performed on a high-temperature Tian-Calvet microcalorimeter. Their enthalpies of formation from the elements, Δ_f H _el ^° (298.15 K) = ?5724 ± 12 (I) and ?5573 ± 14 (II) kJ/mol, were determined by melt solution calorimetry. The Δ_f G _el ^° (298.15 K) = ?5359 ± 12 (I) and ?5231 ± 14 (II) kJ/mol values were calculated. An increase in the content of iron in siderophyllite increased the entropy, enthalpy, and free energy of formation from the elements.     

Standard enthalpy of formation of La2CoO4(cr)

The enthalpies of reactions of La₂CoO₄(cr) and CoCl₂(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La₂CoO₄(cr) at 298.15 K, Δ_f H ^o = ?2179 ± 7 kJ/mol.     

The enthalpies of formation of bis-(benzene)molybdenum and of bis-(toluene)tungsten

Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol^?): ΔH^o_f[Mo(η-C₆H₆)₂, c] = (235.3 ± 8) and ΔH^o_f[W(η⁶-C₇H₈)₂, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔH^o_f(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, $\text{D}$(Mo—benzene) = (247.0 ± 6) and $\text{D}$(W—toluene) = (304.0 ± 6) kJ mol^?1, are derived.     

Thermochemical properties of free radicals from G3MP2B3 calculations

For a set of 32 selected free radicals, energy minimum structures, harmonic vibrational wave numbers ω_e, principal moments of inertia I_A, I_B, and I_C, heat capacities C°_p(T), entropies S°(T), thermal energy contents H°(T) ? H°(0), and standard enthalpies of formation Δ_fH°(T) were calculated at the G3MP2B3 level of theory in the temperature range 200–3000 K. In this article, thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values. The mean absolute deviation between calculated and experimental Δ_fH°(298.15) values resulted in 3.91 kJ mol^?1, which is close to the average experimental uncertainty of ± 3.55 kJ mol^?1. The influence of hindered rotation on thermodynamic functions is studied for isopropyl and tert‐butyl radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 550–560, 2002     

Determination of constant‐volume combustion energy for the complexes of zinc nitrate with three amino acids

Five solid complexes of zinc with L‐α‐methionine, L‐α‐phenylalanine and L‐α‐histidine were prepared. The constant‐volume combustion energies of the complexes, ΔE_c (coordination), were determined by a precise rotating bomb calorimeter at 298.15 K. They were ‐ 2969.03 ± 0.34, ‐2929.46 ± 1.59, ‐9597.13 ± 6.12, ‐4378.98 ± 3.27 and ‐14047 ± 6.75 kJ/mol, respectively. Their standard enthalpies of combustion, ΔH^θ_m,c(coordination, s, 298.15 K), and standard enthalpies of formation, ΔH^θ_m,f (coordination, s, 298.15 K), were calculated. They were ‐2959.73 ± 0.34, ‐2923.88 ± 1.59, ‐9649.18 ± 6.12, ‐4373.40 ± 3.27, ‐14048.53 ± 6.75 kj/mol and ‐1180.94 ± 0.92, ‐1401.26 ± 1.77, ‐2501.69 ± 6.50, ‐1381.47 ± 3.49, ‐1950.19 ± 7.65 kJ/mol, respectively.     

The enthalpies of formation of praseodymium halides PrCl3, PrBr3, and PrI3 in the crystalline state and aqueous solution

The enthalpies of solution of praseodymium tribromide and triiodide in water were measured at 298.15 K in a hermetic isothermic-shell swinging calorimeter. The data obtained and the Δ_f H° (Pr³⁺, sln, ∞H₂O, 298 K) value found earlier were used to calculate the enthalpies of formation of three praseodymium halides (PrCl₃, PrBr₃, and PrI₃) in the crystalline state and aqueous solution.     

The enthalpy of formation of the praseodymium ion (3+) in an infinitely dilute aqueous solution

The enthalpy of reaction between praseodymium metal and 1.07 n HCl and the enthalpy of solution of praseodymium trichloride in 1.07 n HCl and water were measured in a swinging isoperibol calorimeter at 298.15 K. The results were used to calculate the enthalpy of formation of the praseodymium ion in the state of an infinitely dilute aqueous solution, Δ_f H°_298.15 Pr³⁺(sln, ∞H₂O) = ?687.8 ± 1.7 kJ/mol.     

The thermodynamic properties and thermolysis characteristics of 2,5-dimethyl-2,5-di-(m-carboranoylperoxy)-3-hexine and 1,1-dimethyl-2-propine-1-yl diperoxy ester of m-carborane-1,7-dicarboxylic acid

The standard enthalpies of combustion Δ_c H°_298.15 and formation Δ_f H°_298.15 of 2,5-dimethyl-2,5-di-(m-carboranoylperoxy)-3-hexine and 1,1-dimethyl-2-propine-1-yl diperoxy ester of m-carborane-1,7-dicarboxylic acid and the effective activation energy E _eff of their thermolysis were determined for the first time.     

Thermochemistry of fluorine compounds: IV. Rubidium tetrafluoroiodate

From measurement of the heat of hydrolysis, at 25°C , the enthalpy of formation of rubidium tetrafluoroiodate is derived: ΔH°_f [RbIF₄, cryst.]₂₉₈= ?191.12±4.43 kJ mol^?1. Heat capacity measurements for RbIF₄ over the range 273–303 K are also reported.     

Isopiestic Determination of the Osmotic and Activity Coefficients of Li2SO4(aq) at T=298.15 and 323.15 K, and Representation with an Extended Ion-Interaction (Pitzer) Model

Isopiestic vapor-pressure measurements were made for Li₂SO₄(aq) from 0.1069 to 2.8190 mol?kg^?1 at 298.15 K, and from 0.1148 to 2.7969 mol?kg^?1 at 323.15 K, with NaCl(aq) as the reference standard. Published thermodynamic data for this system were reviewed, recalculated for consistency, and critically assessed. The present results and the more reliable published results were used to evaluate the parameters of an extended version of Pitzer’s ion-interaction model with an ionic-strength dependent third-virial coefficient, as well as those of the standard Pitzer model, for the osmotic and activity coefficients at both temperatures. Published enthalpies of dilution at 298.15 K were also analyzed to yield the parameters of the ion-interaction models for the relative apparent molar enthalpies of dilution. The resulting models at 298.15 K are valid to the saturated solution molality of the thermodynamically stable phase Li₂SO₄?H₂O(cr). Solubilities of Li₂SO₄?H₂O(cr) at 298.15 K were assessed and the selected value of m(sat.)=3.13±0.04 mol?kg^?1 was used to evaluate the thermodynamic solubility product K _s(Li₂SO₄?H₂O, cr, 298.15 K) = (2.62±0.19) and a CODATA-compatible standard molar Gibbs energy of formation Δ_f G _m ^o (Li₂SO₄?H₂O, cr, 298.15 K) = ?(1564.6±0.5) kJ?mol^?1.     

Thermodynamique de substances azotees. IX. Etude thermochimique de la benzamide. Comparaison des grandeurs energetiques liees a la structure de quelques amides et thioamides

The enthalpy of sublimation of benzamide was obtained by calorimetry in the range 323<T (K)<350. From values of ΔH_sub(T)=f(T), it was possible to determine ΔH⁰_sub (298.15 K)=101.7±1.0 kJ mole^?1. Using previous data on ΔH⁰_f (c, 298.15 K) obtained by combustion calorimetry, the value of ΔH⁰_f (g, 298.15 K)=?100.9±1.2 kJ mole^?1 was calculated. With the use of energetical values concerning thioacetamide, thiobenzamide and thiourea, on the one hand, and acetamide, benzamide and urea, on the other, a comparative study was made.