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Alexandra Navrotsky - One of the best experts on this subject based on the ideXlab platform.

  • Enthalpy of Formation of zinc acetate dihydrate
    The Journal of Chemical Thermodynamics, 2011
    Co-Authors: James T Hughes, Alexandra Navrotsky
    Abstract:

    Abstract The Enthalpy of Formation of zinc acetate dihydrate (Zn(CH3COO)2 · 2H2O) was measured with respect to crystalline zinc oxide (ZnO), glacial acetic acid (CH3COOH) and liquid water by room temperature solution calorimetry. The Enthalpy of Formation was verified by utilizing two independent thermodynamic cycles, using Enthalpy of solution measurements in 5 mol · L−1 sodium hydroxide (NaOH) and in 5 mol · L−1 hydrochloric acid (HCl) solutions. The Enthalpy of the reaction ZnO (cr) + 2CH3COOH (l) + H2O (l) to form Zn(CH3COO)2 · 2H2O (cr) is –(65.78 ± 0.36) kJ · mol−1 for measurements in 5 mol · L−1 NaOH and –(66.25 ± 0.17) kJ · mol−1 for measurements in 5 mol · L−1 HCl. The standard Enthalpy of Formation of Zn(CH3COO)2 · 2H2O from the elements is –(1669.35 ± 1.30) kJ · mol−1. This work provides the first calorimetric measurement of the Enthalpy of Formation of Zn(CH3COO)2 · 2H2O.

  • mof 5 Enthalpy of Formation and energy landscape of porous materials
    Journal of the American Chemical Society, 2011
    Co-Authors: James T Hughes, Alexandra Navrotsky
    Abstract:

    The first experimental thermodynamic analysis of a metal–organic framework (Mof) has been performed. Measurement of the Enthalpy of Formation of Mof-5 from the dense components zinc oxide (ZnO), 1,4-benzenedicarboxylic acid (H2BDC), and occluded N,N-diethylformamide (DEF) (if any) gave values of 78.64 ± 2.95 and 99.47 ± 3.62 kJ·[mol of Zn4O(BDC)3·xDEF]−1 for the as-made form and the desolvated structure, respectively. These as-made and desolvated enthalpies correspond to the values 19.66 ± 0.74 and 24.87 ± 0.94 kJ·(mol of Zn)−1, respectively. The energetics of desolvated Mof-5 per mole of Zn falls in line with trends relating the Enthalpy of inorganic porous materials (zeolites, zeotypes, and mesoporous materials) to molar volume. Mof-5 extends a plateauing trend first suggested by thermodynamic studies of mesoporous materials. This leveling off of the destabilization energetics as the void space swells suggests that additional void volume beyond a certain point may begin to act as a parameter “external” ...

  • Enthalpy of Formation of carbon rich polymer derived amorphous sicn ceramics
    Journal of the American Ceramic Society, 2008
    Co-Authors: Riham Michelle Morcos, Alexandra Navrotsky, Gabriela Mera, Tamas Varga, Ralf Riedel, Fabrizia Poli, Klaus Muller
    Abstract:

    Carbon-rich silicon carbonitride (SiCN) ceramics derived from polysilylcarbodiimides represent a novel class of materials where the incorporation of a high amount of carbon was demonstrated to be beneficial for ultrahigh-temperature resistance against crystallization. Calorimetric measurements of heat of oxidative dissolution in a molten oxide solvent show that these amorphous SiCN ceramics produced at 1000° or 1100°C possess a small positive or near zero Enthalpy of Formation relative to their crystalline constituents, namely silicon nitride, silicon carbide, and graphite. The Enthalpy of Formation does not change strongly with increasing SiC mole fraction. Because the enthalpies of Formation from crystalline constituents are at most slightly positive, and the entropies of Formation are expected to be significantly positive because of disorder in the amorphous phase, it is likely that the free energies of Formation from silicon carbide, silicon nitride, and graphite are negative and the high-temperature persistence of amorphous SiCN ceramics may originate from thermodynamic stabilization. However, this stabilization is less pronounced than that for SiCO polymer-derived ceramics studied earlier.

  • oxide melt solution calorimetry of selenides Enthalpy of Formation of zinc cadmium and lead selenide
    American Mineralogist, 2008
    Co-Authors: Suraj Deore, Alexandra Navrotsky
    Abstract:

    Selenium is an important trace element. Its geochemical cycles involve various oxidation states, including Se2−, yet thermodynamic data for selenides are sparse. A general method for selenide thermochemistry has been developed by using oxidative drop-solution calorimetry in a molten oxide solvent. The samples are dropped from room temperature into molten sodium molybdate (3Na2O·4MoO3) solvent at 975 K, with oxygen bubbling through the melt to ensure rapid and complete conversion of selenide to dissolved selenate species. This method is analogous to that developed for sulfides (Deore and Navrotsky 2006). Complete dissolution of selenides is documented by furnace tests and visual inspection, and supported by consistent results for Enthalpy. Enthalpies of Formation (Δf H °, kJ/mol) from the elements were determined for zinc selenide (ZnSe) (−169.94 ± 4.31 kJ/mol), cadmium selenide (CdSe) (−139.04 ± 6.13 kJ/mol), and lead selenide (PbSe) (−99.26 ± 6.06 kJ/mol). These three Δf H ° values agree with previously published data, often obtained by less direct means. This is the first report of the Enthalpy of Formation of CdSe measured by any calorimetric method. For ZnSe, a more reliable Δf H ° value is proposed since prior data are quite scattered. The results confirm that oxidative drop-solution calorimetry is an available method for selenide thermochemistry. It should be applicable to binary and multinary selenides with large homogeneity ranges, to solid solutions, and to nanophase materials.

  • Enthalpy of Formation of the cubic fluorite phase in the ceria zirconia system
    Journal of Materials Research, 2008
    Co-Authors: Theresa Lee, C R Stanek, K J Mcclellan, J N Mitchell, Alexandra Navrotsky
    Abstract:

    The Enthalpy of Formation of cubic ceria–zirconia solid solutions (c-Ce(1−x)ZrxO2, 0.05 ⩽ x ⩽ 0.75) at 25 °C with respect to monoclinic zirconia (m-ZrO2) and cubic ceria (c-CeO2) has been measured by high-temperature oxide melt solution calorimetry. In contrast to fluorite solid solutions containing trivalent oxides (e.g., yttria–zirconia), mixing in c-Ce1−xZrxO2 shows moderate positive deviation from ideality. Evaluating the data within the framework of a regular solution model, the interaction parameter, Ω, is +51.0 ± 8.0 kJ/mol. The introduction of undersized Zr into CeO2 severely distorts and destabilizes the oxygen sublattice. Destabilization of c-Ce1−xZrxO2 may be relieved by reduction or clustering. A stable ordered compound in the CeO2–ZrO2 system is thermodynamically unlikely.

Branko Ruscic - One of the best experts on this subject based on the ideXlab platform.

  • Enthalpy of Formation of c2h2o4 oxalic acid from high level calculations and the active thermochemical tables approach
    Journal of Physical Chemistry A, 2019
    Co-Authors: David Feller, Branko Ruscic, David H Bross
    Abstract:

    High-level coupled cluster calculations obtained with the Feller–Peterson–Dixon (FPD) approach and new data from the most recent version of the Active Thermochemical Tables (ATcT) are used to reassess the Enthalpy of Formation of gas-phase C2H2O4 (oxalic acid). The theoretical value was further calibrated by comparing FPD and ATcT gas-phase enthalpies of Formation for H2CO (formaldehyde) and the two low-lying conFormations of C2H4O2 (syn and anti acetic acid). The FPD approach produces a theoretical Enthalpy of Formation of gas-phase oxalic acid of −732.2 ± 4.0 kJ/mol at 298.15 K (−721.8 ± 4.0 kJ/mol at 0 K). An independently obtained ATcT value, based on reassessing the existent experimental determinations and expanding the resulting thermochemical network with select mid-level composite theoretical results, disagrees with several earlier recommendations that were based solely on experimental determinations but is in excellent accord with the current FPD value. The inclusion of the latter in the most rec...

  • active thermochemical tables accurate Enthalpy of Formation of hydroperoxyl radical ho2
    Journal of Physical Chemistry A, 2006
    Co-Authors: Branko Ruscic, Reinhardt Pinzon, Melita L Morton, N K Srinivasan, M C Su, J W Sutherland, J V Michael
    Abstract:

    Through the use of the Active Thermochemical Tables approach, the best currently available Enthalpy of Formation of HO2 has been obtained as ΔfH298°(HO2) = 2.94 ± 0.06 kcal mol-1 (3.64 ± 0.06 kcal mol-1 at 0 K). The related Enthalpy of Formation of the positive ion, HO2+, within the stationary electron convention is ΔfH298°(HO2+) = 264.71 ± 0.14 kcal mol-1 (265.41 ± 0.14 kcal mol-1 at 0 K), while that for the negative ion, HO2- (within the same convention), is ΔfH298°(HO2-) = −21.86 ± 0.11 kcal mol-1 (−21.22 ± 0.11 kcal mol-1 at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 ± 0.14 kcal mol-1 (99.81 ± 0.14 kcal mol-1 at 0 K), while the gas-phase acidity of H2O2 is ΔacidG298°(H2O2) = 369.08 ± 0.11 kcal mol-1, with the corresponding Enthalpy of deprotonation of H2O2 of ΔacidH298°(H2O2) = 376.27 ± 0.11 kcal mol-1 (375.02 ± 0.11 kcal mol-1 at 0 K). In addition, a further improved Enthalpy of Formation of OH is briefly outlined, ΔfH298°(OH) = 8.93 ± 0.03 kcal mol-1 (8.87 ± 0.03 kca...

  • active thermochemical tables accurate Enthalpy of Formation of hydroperoxyl radical ho2
    Journal of Physical Chemistry A, 2006
    Co-Authors: Branko Ruscic, Reinhardt Pinzon, Melita L Morton, N K Srinivasan, J W Sutherland, J V Michael
    Abstract:

    Through the use of the Active Thermochemical Tables approach, the best currently available Enthalpy of Formation of HO2 has been obtained as delta(f)H(o)298 (HO2) = 2.94 +/- 0.06 kcal mol(-1) (3.64 +/- 0.06 kcal mol(-1) at 0 K). The related Enthalpy of Formation of the positive ion, HO2+, within the stationary electron convention is delta(f)H(o)298 (HO2+) = 264.71 +/- 0.14 kcal mol(-1) (265.41 +/- 0.14 kcal mol(-1) at 0 K), while that for the negative ion, HO2- (within the same convention), is delta(f)H(o)298 (HO2-) = -21.86 +/- 0.11 kcal mol(-1) (-21.22 +/- 0.11 kcal mol(-1) at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 +/- 0.14 kcal mol(-1) (99.81 +/- 0.14 kcal mol(-1) at 0 K), while the gas-phase acidity of H2O2 is delta(acid)G(o)298 (H2O2) = 369.08 +/- 0.11 kcal mol(-1), with the corresponding Enthalpy of deprotonation of H2O2 of delta(acid)H(o)298 (H2O2) = 376.27 +/- 0.11 kcal mol(-1) (375.02 +/- 0.11 kcal mol(-1) at 0 K). In addition, a further improved Enthalpy of Formation of OH is briefly outlined, delta(f)H(o)298 (OH) = 8.93 +/- 0.03 kcal mol(-1) (8.87 +/- 0.03 kcal mol(-1) at 0 K), together with new and more accurate enthalpies of Formation of NO, delta(f)H(o)298 (NO) = 21.76 +/- 0.02 kcal mol(-1) (21.64 +/- 0.02 kcal mol(-1) at 0 K) and NO2, delta(f)H(o)298 (NO2) = 8.12 +/- 0.02 kcal mol(-1) (8.79 +/- 0.02 kcal mol(-1) at 0 K), as well as H(2)O(2) in the gas phase, delta(f)H(o)298 (H2O2) = -32.45 +/- 0.04 kcal mol(-1) (-31.01 +/- 0.04 kcal mol(-1) at 0 K). The new thermochemistry of HO2, together with other arguments given in the present work, suggests that the previous equilibrium constant for NO + HO2 --> OH + NO2 was underestimated by a factor of approximately 2, implicating that the OH + NO2 rate was overestimated by the same factor. This point is experimentally explored in the companion paper of Srinivasan et al. (next paper in this issue).

J V Michael - One of the best experts on this subject based on the ideXlab platform.

  • active thermochemical tables accurate Enthalpy of Formation of hydroperoxyl radical ho2
    Journal of Physical Chemistry A, 2006
    Co-Authors: Branko Ruscic, Reinhardt Pinzon, Melita L Morton, N K Srinivasan, M C Su, J W Sutherland, J V Michael
    Abstract:

    Through the use of the Active Thermochemical Tables approach, the best currently available Enthalpy of Formation of HO2 has been obtained as ΔfH298°(HO2) = 2.94 ± 0.06 kcal mol-1 (3.64 ± 0.06 kcal mol-1 at 0 K). The related Enthalpy of Formation of the positive ion, HO2+, within the stationary electron convention is ΔfH298°(HO2+) = 264.71 ± 0.14 kcal mol-1 (265.41 ± 0.14 kcal mol-1 at 0 K), while that for the negative ion, HO2- (within the same convention), is ΔfH298°(HO2-) = −21.86 ± 0.11 kcal mol-1 (−21.22 ± 0.11 kcal mol-1 at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 ± 0.14 kcal mol-1 (99.81 ± 0.14 kcal mol-1 at 0 K), while the gas-phase acidity of H2O2 is ΔacidG298°(H2O2) = 369.08 ± 0.11 kcal mol-1, with the corresponding Enthalpy of deprotonation of H2O2 of ΔacidH298°(H2O2) = 376.27 ± 0.11 kcal mol-1 (375.02 ± 0.11 kcal mol-1 at 0 K). In addition, a further improved Enthalpy of Formation of OH is briefly outlined, ΔfH298°(OH) = 8.93 ± 0.03 kcal mol-1 (8.87 ± 0.03 kca...

  • active thermochemical tables accurate Enthalpy of Formation of hydroperoxyl radical ho2
    Journal of Physical Chemistry A, 2006
    Co-Authors: Branko Ruscic, Reinhardt Pinzon, Melita L Morton, N K Srinivasan, J W Sutherland, J V Michael
    Abstract:

    Through the use of the Active Thermochemical Tables approach, the best currently available Enthalpy of Formation of HO2 has been obtained as delta(f)H(o)298 (HO2) = 2.94 +/- 0.06 kcal mol(-1) (3.64 +/- 0.06 kcal mol(-1) at 0 K). The related Enthalpy of Formation of the positive ion, HO2+, within the stationary electron convention is delta(f)H(o)298 (HO2+) = 264.71 +/- 0.14 kcal mol(-1) (265.41 +/- 0.14 kcal mol(-1) at 0 K), while that for the negative ion, HO2- (within the same convention), is delta(f)H(o)298 (HO2-) = -21.86 +/- 0.11 kcal mol(-1) (-21.22 +/- 0.11 kcal mol(-1) at 0 K). The related proton affinity of molecular oxygen is PA298(O2) = 100.98 +/- 0.14 kcal mol(-1) (99.81 +/- 0.14 kcal mol(-1) at 0 K), while the gas-phase acidity of H2O2 is delta(acid)G(o)298 (H2O2) = 369.08 +/- 0.11 kcal mol(-1), with the corresponding Enthalpy of deprotonation of H2O2 of delta(acid)H(o)298 (H2O2) = 376.27 +/- 0.11 kcal mol(-1) (375.02 +/- 0.11 kcal mol(-1) at 0 K). In addition, a further improved Enthalpy of Formation of OH is briefly outlined, delta(f)H(o)298 (OH) = 8.93 +/- 0.03 kcal mol(-1) (8.87 +/- 0.03 kcal mol(-1) at 0 K), together with new and more accurate enthalpies of Formation of NO, delta(f)H(o)298 (NO) = 21.76 +/- 0.02 kcal mol(-1) (21.64 +/- 0.02 kcal mol(-1) at 0 K) and NO2, delta(f)H(o)298 (NO2) = 8.12 +/- 0.02 kcal mol(-1) (8.79 +/- 0.02 kcal mol(-1) at 0 K), as well as H(2)O(2) in the gas phase, delta(f)H(o)298 (H2O2) = -32.45 +/- 0.04 kcal mol(-1) (-31.01 +/- 0.04 kcal mol(-1) at 0 K). The new thermochemistry of HO2, together with other arguments given in the present work, suggests that the previous equilibrium constant for NO + HO2 --> OH + NO2 was underestimated by a factor of approximately 2, implicating that the OH + NO2 rate was overestimated by the same factor. This point is experimentally explored in the companion paper of Srinivasan et al. (next paper in this issue).

O. J. Kleppa - One of the best experts on this subject based on the ideXlab platform.

  • standard Enthalpy of Formation of cu3as and heats of mixing in the liquid systems cuas and feas by direct combination high temperature drop calorimetry
    Journal of Alloys and Compounds, 1995
    Co-Authors: Jan Wypartowicz, K Fitzner, O. J. Kleppa
    Abstract:

    Abstract The standard Enthalpy of Formation of the congruent melting compound Cu 3 As (m.p. 1000 K) was determined by high temperature direct synthesis drop calorimetry in fused silica capsules at 1113 K. We found ΔH f o (298 K) = −14.6 ± 3.8 kJ mol −1 . Using our measured values of the heats of reaction of the process a As(s)+ b Cu(s) → c Cu 1− x As x (1) at 1113 K, we calculated the liquid-liquid enthalpies of mixing for three alloy compositions in Cu 1− x As x : x =0.235, 0.26 and 0.375. We carried out similar measurements at 1123 K for the eutectic alloy Fe 1− x As x (1) at x = 0.24. The calorimetric results for the solid and liquid alloys are compared with predicted values from Miedema's semiempirical model.

  • Enthalpy change of the reaction 3 2 enstatite corundum pyrope and the Enthalpy of Formation of pyrope
    Geochimica et Cosmochimica Acta, 1992
    Co-Authors: James O Eckert, Robert C Newton, O. J. Kleppa
    Abstract:

    Abstract The Enthalpy of Formation (ΔHf0) of pyrope has been redetermined by solution calorimetry in lead borate solvent at 700°C (973 K) on synthetic pyrope and on mixtures of synthetic enstatite + corundum on pyrope composition. Attempts to obtain ΔHf0 more directly by dissolving oxide mixtures on pyrope composition failed because of incomplete dissolution of MgO. ΔHf0 (pyrope) is obtained from the reaction 3 2 Mg 2 Si 2 O 6 + Al 2 O 3 = Mg 3 Al 2 Si 3 0 12 enstatite corrundum pyrope, using measured solution values for each side of the reaction combined with an Enthalpy of Formation of enstatite. Measured solution values for reaction (A), at 973 K, are (kJ/mole) as follows: ΔH sol ( 3 2 En + Cor) = 139.22 ± 3.74, n = 14 ΔHsol(Py) = 111.49 ± 2.18, n = 19. Uncertainties are twice the standard deviations on the means (δ). Using these values and the ΔHf,10730 (enstatite) from alkali borate solution calorimetry of Brousse et al. (1984) on synthetic enstatite, the calculated Enthalpy of Formation of pyrope at 298 K, corrected with measured heat content data, is ΔHf,2980 (Py) = −72.01 ± 6.98 kJ/mole. This value agrees well with the −70.96 kJ/mole value from the internally consistent dataset of Holland and Powell (1990) and with the value of Berman (1988) of −74.25 kJ/mole. This agreement indicates that major discrepancies no longer exist between thermodynamic measurements and experimental phase equilibrium data for pyrope. Anomalous solution behavior of MgO in Pb2B2O5, most likely incomplete dissolution, is the most probable reason for the substantially more negative ΔHf0 of pyrope found by Charlu et al. (1975).

A L Smith - One of the best experts on this subject based on the ideXlab platform.

  • mass spectrometric study of the vaporization behaviour of α na2npo4 thermodynamic investigation of the Enthalpy of Formation
    The Journal of Chemical Thermodynamics, 2013
    Co-Authors: A L Smith, J Y Colle, O Benes, Attila Kovacs, Philippe E Raison, R J M Konings
    Abstract:

    Abstract The work herein presents the first high temperature Knudsen effusion mass spectrometric measurements carried out on the sodium neptunate α-Na2NpO4. The material’s vaporization behaviour was investigated under vacuum conditions, in a tungsten metal cell up to T = 2700 K, and in an alumina cell up to T = 1900 K. Gaseous and condensed phases are in equilibrium under Knudsen conditions. The equilibrium decomposition reaction of α-Na2NpO4 to neptunium oxide, sodium oxide, and oxygen was established in the temperature range 1030 K to 1206 K. The Enthalpy of Formation of α-Na2NpO4 at 298.15 K was furthermore estimated at (−1761.0 ± 7.7) kJ·mol−1 using a second law analysis in the interval 1030 K to 1115 K, in good agreement with the value reported by Goudiakas et al.  [25] (−1763.9 ± 7) kJ·mol−1, who used solution calorimetry. In the interval 1115 K to 1206 K, where the vaporization of sodium oxide formed by decomposition of α-Na2NpO4 is considered, the analysis yielded at 298.15 K (−1761.9 ± 20.4) kJ·mol−1 and (−1758.8 ± 22.3) kJ·mol−1 taking into account two different sodium oxide sublimation mechanisms suggested by Hildenbrand and Lau [56] and Steinberg and Schofield [37] respectively. Finally, the detection of the masses 253 and 292 in the temperature range 1350 to 1620 K suggests a probable sublimation of the high temperature tetragonal phase of the Na2NpO4 compound in parallel with the decomposition. The method developed in the present paper holds promise for the thermodynamic investigation of other sodium neptunates and plutonates phases.