Determination calorimetrique de l'enthalpie de formation des alliages (Al,Ba) riches en aluminum

The heats of formation of some aluminium-barium alloys have been determined by drop calorimetry at high temperature. The heats of mixing of pure liquid Al and Ba to give the liquid alloy are Δ_mH(x_Ba=O.056, 1215 K)=?6.6 kJ mole^?1 and Δ_mH(x_Ba=O.333, 1215 K)=?31.0 kJ mole^-1. To measure its heat of formation, the solid compound Al₄Ba was precipitated by addition of pure barium from a liquid (Al, Ba) bath. It was found that Δ_fH(Al_0.8Ba_O.2, solid, 1215 K)=-(37.1 ? 1.5) kJ mole^?1 with reference to the pure metals in the solid state.     

Thermodynamics of redox reactions involving nicotinamide adenine dinucleotide

Literature data on the thermodynamics of redox nicotinamide adenine dinucleotide (NAD) dependent reactions have been analyzed. It has been established that for the redox reaction of NAD

where all substances except H₂ are in the aqueous buffer with the ionization enthalpy equal to zero, the most reliable thermodynamic parameters should be considered as: ΔH(298.15 K; pH 7)=?27.4±1.7 kJ mole^?1; ΔG (298.15K; pH 7)=±17.8 kJ mole^?1. From the above thermodynamic parameters of the reaction ΔH, ΔG and ΔS for reactions of NAD with natural substrates, synthetic mediators and some inorganic compounds have been calculated.     

Enthalpy of the formation of natural hydrous aluminum hydroxosulfate (aluminite)

A thermochemical study of natural aluminum hydroxosulfate Al₂[(OH)₄SO₄] · 7H₂O, aluminite (Nakhodka deposit, West Chukotka, Russia) is performed on a Tian-Calvet “Setaram” high-temperature heat-conducting microcalorimeter (France). The enthalpy of aluminite formation from simple compounds is obtained via the melt calorimetry of dissolution, Δ_f H ^○(298.15 K) = ?4986 ± 21 kJ/mol.     

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.     

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.     

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).     

Thermochemical investigation of natural antlerite

Thermal and thermochemical investigations of natural hydroxyl-bearing copper sulfate Cu₃SO₄(OH)₄??antlerite have been carried out. The stages of its thermal decomposition have been studied employing the Fourier-transform IR spectroscopy. The enthalpy of formation of antlerite from the elements ??_f H _m ^o (298.15?K)?=?(?1750?±?10)?kJ?mol^?1 has been determined by the method of oxide melt solution calorimetry. Using value of S _m ^o (298.15?K), equal to (263.46?±?0.47)?J?K^?1?mol^?1, obtained earlier by the method of adiabatic calorimetry, the Gibbs energy value of ??_f G _m ^o (298.15?K)?=?(?1467?±?10)?kJ?mol^?1 has been calculated.     

Integral heat of dissolution of potassium chlorate in water at 298.15 K

The heat of dissolution of potassium chlorate in water at 298.15 K has been measured on an LKB 8700-1 calorimeter in the concentration range 0.063–0.659 m. The concentration dependence of the measured data was fitted by an empirical equation ΔH_m (kJ mole^?1) = 41.353₈ + 1.862₆m^{$\text{1}\text{2}$} ? 6.430₀m which was derived from our and Andauer—Lange data. The heat of crystallization calculated from this dependence was ΔH_cryst. = 34.7 ± 0.5 kJ mole^?1, which agrees with data calculated for potassium chlorate from solubility and activity data.     

Kinetische untersuchung der reversiblen dimerisierung von o-phenylendioxidimethylsilan

The reversible dimerisation of o-phenylenedioxydimethylsilane (2,2-dimethyl-1,3,2-benzodioxasilole) has been studied by ¹H NMR spectroscopy. The kinetics of this reaction can be described quantitatively by a bimolecular 10-ring formulation reaction and a monomolecular backreaction. The thermodynamic and kinetic parameters are: ΔH⁰ = ?43 kJ mol^?1; ΔS⁰ = ?112 J mol^?1 K^?1; ΔG⁰₂₉₈ = ?9.6 kJ mol^?1; ΔH³₂₉₈ = 57 kJ mol^?1; ΔS³₂₉₈ = ?129 J mol^?1 K^?1; ΔG³₂₉₈ = 96 kJ mol^?1; E_a = 60 kJ mol^?1; A = 3.17 × 10⁶ l mol^?1 s^?1. Remarkable is the low activation energy of formation of the ten-membered ring, considering that two SiO bonds have to be cleaved during the reaction. Transition states and possible structures of the ten-membered heterocycle are 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.     

Equilibrium sublimation and thermodynamic properties of SnS

Knudsen effusion studies of the sublimation of polycrystalline SnS, prepared by annealing and chemical vapor transport, have been performed employing vacuum micro-balance techniques in the temperature range 733–944 K and at pressures ranging from about 6 × 10^?3 to 11 Pa.The third-law heats of sublimation and second-law entropy of reaction SnS(s) = SnS(g) were determined to be ΔH⁰₂₉₈ = 220.4 ± 3.0 kJ mole^? and ΔS⁰₂₉₈ = 162.4 ± 4.5 J K^?1 mole^?1. From these data the standard heat of formation and absolute entropy of SnS(s) were calculated to be ?102.9 ± 4.0 kJ mole^?1 and 79.9 ± 6.0 J K^?1, respectively.     

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.     

Phase equilibria and thermodynamics of the double oxide phase Cu3TiO4

Phase equilibria in the system CuCu₂OTiO₂ were investigated in the temperature range of 1160–1270 K by means of thermogravimetry and measurements of the oxygen partial pressure. The tie lines on the isothermal phase diagram run from the phase Cu₃TiO₄ to CuO, Cu₂O, and TiO₂. The existence of Cu₃TiO₅ and Cu₂TiO₃ could not be confirmed in this temperature range. The phase “Cu₃TiO₄” is only stable above about 1140 K and its composition fluctuates between about Cu₃TiO_4.3 and Cu₃TiO_3.9. The formation of Cu₃TiO_4.3 according to the reaction 1.6 CuO + 0.7 Cu₂O + TiO₂ = Cu₃TiO_4.3 is endothermic: (1160 < T < 1270 K) ΔH° = (7600 ± 450 J-mole^?1; ΔS° = (6.7 ± 0.4) J·K^?1·mole^?1. The standard Gibbs free energy, enthalpy, and entropy of formation of Cu₃TiO_4.3 at 1200 K are ΔG°_f = ?101.39 kJ, ΔH°_f = ?1115.84 kJ, and S°_f = 466.76 J·K^?1. Rather similar values were found for Cu₃TiO_3.9.     

The thermodynamic characteristics of natural iron-lithium micas

A thermochemical study of natural lithium micas, iron-containing polylithionite and lepidolite, was performed on a high-temperature heat-flux Calvet microcalorimeter (Setaram, France). Melt solution calorimetry was used to measure the enthalpies of mineral formation from the elements Δ_f H°_el (298.15 K), ?5989.3 ± 9.6 and ?5981.3 ± 6.3 kJ/mol, respectively. The drop method was used to determine the enthalpy increments heating of the micas over the temperature interval 444–973 K. The equations for the temperature dependences of the heat capacities and enthalpies of Fe-polylithionite and Fe-lepidolite were obtained. The S° (298.15 K) and Δ_f G°_el (298.15 K) values were estimated. The thermodynamic functions of the micas were calculated over the temperature range 298.15–1000 K.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

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.     

Die Bildungsenthalpie von Zinndijodid,SnJ2 (c)

The heat of reaction for SnJ₂ (c)+J₂ (c)+4045 CS₂ (l)=[SnJ₄; 4045 CS₂] (sol) has been determined to be (?41.12±0.55) kJ mol^?1, [(?9.83±0.13) kcal mol^?1] by isoperibol solution calorimetry. Combining this result with the heat of formation of SnJ₄ in CS₂ determined in a previous investigation¹¹ the value (?153.9±1.40) kJ mol^?1, [(?36.9±0.33) kcal mol^?1] has been derived for the heat of formation, ΔH _f ^ι (SnJ₂;c; 298.15 K), of tin diiodide.     

Thermodynamic properties of aluminum monooxycarbide Al2OC

It was shown that the published data on the thermodynamic properties of aluminum monooxycarbide Al₂OC (ed) are not consistent with the phase diagram of the Al₂O₃-Al₄C₃ system. A thermodynamic modeling of the equilibrium state of the Al₂O₃-Al₄C₃ system made it possible to obtain new estimates of the standard entropy and enthalpy of formation of aluminum monooxycarbide: S°(298.15 K, cd. Al₂OC) = 45.3 J/(K mol) and Δ_f H°(298.15 K, cd, Al₂OC) = ?625.6 kJ/mol.     

Thermodynamic properties of citric acid and the system citric acid-water

The binary system citric acid-water has been investigated with static vapour pressure measurements, adiabatic calorimetry, solution calorimetry, solubility measurements and powder X-ray measurements. The data are correlated by thermodynamics and a large part of the phase diagram is given. Molar heat capacities of citric acid are given from 90 to 330 K and for citric acid monohydrate from 120 to 300 K. The enthalpy of compound formation Δ_comH (298.15 K)=(?11.8±1) kJ mole^?1.     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.