Calorimetric determination enthalpy of the formation of natural pyromorphite

A calorimetric study of natural pyromorphite Pb₅[PO₄]₃Cl was performed. Its enthalpy of formation was determined by melt solution calorimetry from elements Δ_f H _el^∘(298.15 K) = −4124 ± 20 kJ/mol. Value Δ_f G _el^o(298.15 K) = −3765 ± 20 kJ/mol was calculated.     

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.     

Stationary points on the energy hypersurface of the reaction O3 + H•→ [•O3H]* ⇆ O2 + •OH and thermodynamic functions of •O3H at G3MP2B3, CCSD(T)-CBS (W1U) and MR-ACPF-CBS levels of theory

The relative enthalpies, ΔH^o (0) and ΔH^o (298.15), of stationary points (four minimum and three transition structures) on the ^•O₃H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which we earlier found mean absolute deviations (MAD) of 3.9 kJ mol⁻¹ and 2.3 kJ mol⁻¹, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For CCSD(T)-CBS (W1U) the well depth from O₃ + H^• to trans-^•O₃H, ΔH^o_well(298.15) = −339.1 kJ mol⁻¹, as well as the reaction enthalpy of the overall reaction O₃ + H^•→O₂ + ^•OH, Δ_rH^o(298.15) = −333.7 kJ mol⁻¹, and the barrier of bond dissociation of trans-^•O₃H → O₂ + ^•OH, ΔH^o(298.15) = 22.3 kJ mol⁻¹, affirm the stable short-lived intermediate ^•O₃H. In addition, for radicals cis-^•O₃H and trans-^•O₃H, the thermodynamic functions heat capacity C^o_p(T), entropy S^o (T), and thermal energy content H^o(T) − H^o(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-^•O₃H resulted to be Δ_fH^o(298.15) = 31.1 kJ mol ⁻¹ and 32.9 kJ mol ⁻¹, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied to consider possible multiconfiguration effects and yield Δ_fH^o(298.15) = 21.2 kJ mol ⁻¹. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol⁻¹ is still unresolved. Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental value of Δ_fH^o(298.15) = 29.7 ± 8.4 kJ mol⁻¹ in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress).     

The thermodynamic properties of S-lactic acid

The enthalpies of combustion and formation of S-lactic acid at 298.15 K, Δ_c H _m^o(cr.) = −1337.9 ± 0.8 and Δ_f H _m^o(cr.) = −700.1 ± 0.9 kJ/mol, were determined by calorimetry. The temperature dependence of acid vapor pressure was studied by the transpiration method, and the enthalpy of its vaporization was obtained, Δ_vap H ^o(298.15 K) = 69.1 ± 1.0 kJ/mol. The temperature and enthalpy of fusion, T _m (330.4 K) and Δ_m H ^o(298.15 K) = 14.7 ± 0.2 kJ/mol, were determined by differential scanning calorimetry. The enthalpy of formation of the acid in the gas phase was obtained. Ab initio methods were used to perform a conformational analysis of the acid, calculate fundamental vibration frequencies, moments of inertia, and total and relative energies of the stablest conformers. Thermodynamic properties were calculated in the ideal gas state over the temperature range 0–1500 K. A thermodynamic analysis of mutual transformation processes (the formation of SS- and RS(meso)-lactides from S-lactic acid and the racemization of these lactides) and the formation of poly-(RS)-lactide from S-lactic acid and SS- and RS(meso)-lactides was performed.     

The heat capacity and thermodynamic functions of pyromorphite over the temperature range 5–320 K

The heat capacity of natural mineral, pyromorphite Pb₅(PO₄)₃Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy, and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The standard thermodynamic functions of the mineral are C _p298.15^o = 414.98 ± 0.44 J/(mol K), S _298.15^o = 585.31 ± 0.99 J/(mol K), H _298.15^o − H ₀^o = 80.90 ± 0.08 kJ/mol, and Φ_298.15^o = 313.97 ± 0.84 J/(mol K).     

Calorimetric determination of the enthalpy of formation for pyrophyllite

A calorimetric study of the natural pyrophyllite was performed by high-temperature melt calorimetry on a Tian-Calvet calorimeter. Based on experimentally determined in this work for pyrophyllite and gibbsite, as well as previously obtained for corundum and quartz, the total value of the enthalpy increment for the sample heated from room temperature to 973 K and the enthalpy of dissolution at 973 K by Hess’s law, the enthalpy of formation of pyrophyllite of Al₂[(OH)₂/Si₄O₁₀] composed of elements was calculated at 298.15 K: Δ_f H _el^o(298.15 K) = −5639.8 ± 5.7 kJ/mol.     

The structure and thermochemistry of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1) and some related compounds

Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol⁻¹, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol⁻¹) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol⁻¹) adjusted from DSC measurements at the melting temperature (1, (T _fus, 357.7 K, 16.9 ± 1.3 kJ mol⁻¹)); 2, (T _fus, 383.3 K, 10.9 ± 0.1) kJ mol⁻¹) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol⁻¹) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol⁻¹) and 7-heptadecanone ((94.5 ± 1.8) kJ mol⁻¹) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T _fus, 312.7 K, 18.4 ± 0.5) kJ mol⁻¹) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound 1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone.     

Enthalpy of formation of talc Mg<Subscript>3</Subscript>[Si<Subscript>4</Subscript>O<Subscript>10</Subscript>](OH)<Subscript>2</Subscript> according to dissolution calorimetry

A thermochemical study of natural talc was performed by high-temperature melt dissolution calorimetry on a Tian-Calvet calorimeter. Based on the total values of the increment in enthalpy upon heating the sample from room temperature to 973 K, and of the dissolution enthalpy at 973 K measured in this work for talc and gibbsite (along with those determined for tremolite, brucite, and their corresponding oxides), the enthalpy of formation was calculated for talc composed of elements, Mg₃[Si₄O₁₀](OH)₂, at 298.15 K: Δ_f H _el^o(298.15 K) = −5900.6 ± 4.7 kJ/mol.     

The thermodynamic properties of natural margarite

Thermal, IR spectroscopic, and thermochemical studies of natural brittle mica, margarite Ca_1.00Na_0.10Mg_0.02Al_3.89Fe_0.01³⁺Si_2.03Ti_0.01O₁₀(OH)_1.74F_0.26, were performed. The enthalpy of formation of natural margarite from the elements (−6269 ± 12 kJ/mol) was determined by melt solution calorimetry on a high-temperature heat-conducting Calvet microcalorimeter (Setaram, France). Enthalpy growth over the temperature range 298.15–973 K was determined by the drop method. Equations for the temperature dependences of the enthalpy and heat capacity were obtained, H°(T)−H°(298.15 K), J/mol = 435.21T + 36.46 × 10⁻³ T ² + 109.91 × 10⁵/T − 169863 and C° _p , J/(mol K) = 435.21 + 72.92 × 10⁻³ T − 109.91 × 10⁵/T ². The experimental data were used to estimate the thermodynamic properties of margarite of the theoretical composition, CaAl₂[Al₂Si₂O₁₀](OH)₂.     

Thermochemical properties of trialkylarsenites

The heats of the reaction of sodium with ethyl and methyl alcohol were determined by calorimetry. The difference in the standard heats of the formation of triethylarsenite and arsenic trichloride was obtained by calorimetration of the reaction of arsenic trichloride with sodium ethylate, the value of which was −382.42 ± 3.60 kJ/mol. The standard enthalpies of formation were determined from a critical analysis of all data on thermochemistry of trialkylarsenites for the following compounds: triethylarsenite Δ_f H ₂₉₈^ℴ [(C₂H₅O)₃As(liquid)] = (−704.38 ± 3.85) kJ/mol; trimethylarsenite Δ_f H ₂₉₈^ℴ [(CH₃O)₃As(liquid)] = (−599.36 ± 1.88) kJ/mol. The values of standard enthalpies of formation were not adjusted for the following substances in liquid state: arsenic trichloride (−321.96 ± 3.85 kJ/mol), tris-(diethylamido)arsenic(III) As(NEt₂)₃(liquid) (−129.81 ± 4.41 kJ/mol), tri-n-propylarsenite (−720.61 ± 4.49 kJ/mol), triisopropylarsenite (−756.11 ± 4.65 kJ/mol), tri-n-butylarsenite (−775.11 ± 4.53 kJ/mol), and triisobutylarsenite (−809.71 ± 4.59 kJ/mol). The use of sodium alcoxide solutions for the calorimetration of halogen anhydrides of various acids was demonstrated.     

Heat capacity,enthalpy and entropy of calcium niobates

Heat capacity and enthalpy increments of calcium niobates CaNb₂O₆ and Ca₂Nb₂O₇ were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (669–1421 K). Temperature dependencies of the molar heat capacity in the form C _pm=200.4+0.03432T−3.450·10⁶/T ² J K⁻¹ mol⁻¹ for CaNb₂O₆ and C _pm=257.2+0.03621T−4.435·10⁶/T ² J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇ were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S _m⁰(CaNb₂O₆, 298.15 K)=167.3±0.9 J K⁻¹ mol⁻¹ and S _m⁰(Ca₂Nb₂O₇, 298.15 K)=212.4±1.2 J K⁻¹ mol⁻¹, were evaluated from the low temperature heat capacity measurements. Standard enthalpies of formation at 298.15 K were derived using published values of Gibbs energy of formation and presented heat capacity and entropy data: Δ_f H ⁰(CaNb₂O₆, 298.15 K)= −2664.52 kJ mol^t-1 and Δ_f H ⁰(Ca₂Nb₂O₇, 298.15 K)= −3346.91 kJ mol⁻¹.     

Low-temperature heat capacity and standard entropy of PdO(cr.)

The temperature dependence of the heat capacity C _p ^o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86 K. Standard thermodynamic functions C _p ^o(T), H ^o(T) — H ^o(0), S ^o(T), and G ^o(T) — H ^o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium oxide are recommended: S ^o(298.15) = 39.58 ± 0.15 J/(K mol), Δ_f H ^o(298.15) = −112.69 ± 0.32 kJ/mol, Δ_f G ^o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)₂ (amorph.) with respect to PdO(cr.) was estimated.     

Thermodynamic investigation of several natural polyols

The low-temperature heat capacity C _p,m of erythritol (C₄H₁₀O₄, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C _p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol⁻¹ and 97.17±0.49 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions [H _T-H _298.15] and [S _T-S _298.15], were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δ_c H _m⁰(C₄H₁₀O₄, cr)= −2102.90±1.56 kJ mol⁻¹ and Δ_f H _m⁰(C₄H₁₀O₄, cr)= − 900.29±0.84 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.     

Thermodynamic properties of strontium metaniobate SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

The heat capacity and the enthalpy increments of strontium metaniobate SrNb₂O₆ were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C _pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·10⁶/T ² J K⁻¹ mol⁻¹ (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S _m⁰ (298.15 K)=173.88±0.39 J K⁻¹ mol⁻¹ was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δ_f H ⁰ (298.15 K)=-2826.78 kJ mol⁻¹ was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.     

Thermochemistry of the ternary solid complex Gd(C5H8NS2)3(C12H8N2)

The novel ternary solid complex Gd(C₅H₈NS₂)₃(C₁₂H₈N₂) has been obtained from the reaction of hydrous gadolinium chloride, ammonium pyrrolidinedithiocarbamate (APDC), and 1,10-phenanthroline (o-phen · H₂O) in absolute ethanol. The complex was described by an elemental analysis, TG-DTG, and an IR spectrum. The enthalpy change of the complex formation reaction from a solution of the reagents, Δ_r H _m ^ϑ (sol), and the molar heat capacity of the complex, c _m , were determined as being − 15.174 ± 0.053 kJ/mol and 72.377 ± 0.636 J/(mol K) at 298.15 K by using an RD496-III heat conduction microcalorimeter. The enthalpy change of a complex formation from the reaction of the reagents in a solid phase, Δ_r H _m ^ϑ (s), was calculated as being 52.703 ± 0.304 kJ/mol on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of the formation reaction of the complex was investigated by the reaction in solution. Fundamental parameters, the activation enthalpy (ΔH _≠ ^ϑ ), the activation entropy (ΔS _≠ ^ϑ ), the activation free energy (ΔG _≠ ^ϑ ), the apparent reaction rate constant (k), the apparent activation energy (E), the preexponential constant (A), and the reaction order (n), were obtained by the combination of the thermochemical data of the reaction and kinetic equations, with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, Δ_c U, was determined as being −17588.79 ± 8.62 kJ/mol by an RBC-II type rotatingbomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_c H _m ^ϑ , and standard enthalpy of formation, Δ_f H _m ^ϑ , were calculated to be −17604.28 ± 8.62 and −282.43 ± 9.58 kJ/mol, respectively. The text was submitted by the authors in English.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

The thermodynamic stability of the LaBr 4 − ion

The thermodynamic stability of the LaBr ₄ ^? anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction $ LaBr_4^ - = Br^ - + LaBr_3 The thermodynamic stability of the LaBr₄⁻ anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction were Δ_r H°(298.15 K) = 302 ± 14 and 303 kJ/mol, respectively. The value Δ_f H° (LaBr₄⁻, g, 298.15 K) = −1105 ± 14 kJ/mol was recommended as the enthalpy of formation of the LaBr₄⁻ anion. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, D.A. Ivanov, V.V. Sliznev, K.W. Kr?mer, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 5, pp. 885–890.     

Enthalpy of formation of BaCe<Subscript>0.9</Subscript>In<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>(s)

Enthalpy of formation of the perovskite-related oxide BaCe_0.9In_0.1O_2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl₂, CeCl₃, InCl₃ in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe_0.9In_0.1O_2.95 has been calculated as −1611.7±2.6 kJ mol⁻¹. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δ_ox H ⁰ (298.15 K)=−36.2±3.4 kJ mol⁻¹.     

Thermochemical studies on the thioproline

The combustion energy of thioproline was determined by the precision rotating-bomb calorimeter at 298.15 K to be Δ_c U= –2469.30±1.44 kJ mol^–1. From the results and other auxiliary quantities, the standard molar enthalpy of combustion and the standard molar enthalpy of formation of thioproline were calculated to be Δ_c H _m ^θC₄H₇NO₂S, (s), 298.15 K= –2469.92±1.44 kJ mol^–1 and Δ_f H _m ^θC₄H₇NO₂S, (s), 298.15K= –401.33±1.54 kJ mol^–1.     

Standard enthalpy of formation of nickel trifluoride by isothermal calorimetry

The change in enthalpy in reactions of NiF₃(s) with water and aqueous solution of potassium hydroxide are measured in the isothermal calorimetry mode at 298.15 K. The standard enthalpy of formation Δ_f H° of nickel trifluoride was found to be −816 ± 6 kJ/mol.