Standard molar enthalpy of formation of rubidium diphosphate

Rubidium carbonate (Rb₂CO₃) and ammonium dihydrogen phosphate (NH₄H₂PO₄) were used for synthesizing rubidium diphosphate (Rb₄P₂O₇). The purity of the latter compound was checked up by X-ray diffraction. Rb₄P₂O₇ was involved in an hypothetical reaction and dissolved together with the other components in a 3.85 % (m/m) phosphoric acid solution, using a C-80 SETARAM calorimeter. Mixing processes were also realized in the calorimeter in order to get the standard molar enthalpy of formation of rubidium diphosphate (Rb₄P₂O₇). For that a thermochemical cycle was investigated and the obtained value for the standard molar enthalpy of formation of rubidium diphosphate is (?3,183.7) kJ mol^?1. The result is about 1.8 % lower than literature value.     

High-symmetry polymorph of anhydrous disodium hydrogen phosphate

A new Na₂HPO₄ polymorph was prepared with space group Fddd, Z = 8, a = 5.8426(3) Å, b = 9.7908(5) Å, c = 12.2673(5) Å. The crystal structure includes PO₄ tetrahedra and Na atoms, each surrounded by six O atoms positioned in the corners of a heavily distorted octahedron. The proton is equiprobably disordered over the O atoms.     

Standard enthalpy of formation of lanthanum oxybritholites

Lanthanum-bearing silicate-oxyapatites or britholites, Ca_10–xLax(PO₄)_6–x(SiO₄)_xO with 1≤x≤6, have been synthesized by solid state reaction at high temperature. They were characterized by X-ray diffraction and IR spectroscopy. Using two microcalorimeters, the heat of solution of these compounds have been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained least squares method was applied to the experimental results to obtain the solution enthalpies at infinite dilution, and the mixing enthalpy in two steps. In the first step the mixing enthalpy obtained is referenced to the britholite monosubstituted and to the oxysilicate. The mixing enthalpy referenced to the oxyapatite and to the oxysilicate is then extrapolated. In order to determine the enthalpies of formation of all the terms of the solution, thermochemical cycles were proposed and complementary experiments were performed. The results obtained show a decrease of the enthalpy of formation with the amount of Si and La introduced in the lattice. This was explained by the difference in the bond energies of (Ca–O, P–O) and (La–O, Si–O).     

Standard enthalpy of formation of platinum hydrous oxide

Standard enthalpies of formation of amorphous platinum hydrous oxide PtH_2.76O_3.89 (Adams' catalyst) and dehydrated oxide PtO_2.52 at T=298.15 K were determined to be -519.6±1.0 and -101.3 ±5.2 kJ mol^-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO₂ was estimated to be -80 kJ mol^-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation energy is 246 kJ mol^-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide an energetic reason why platinum hydrous oxide is non-stoichiometric. This revised version was published online in August 2006 with corrections to the Cover Date.     

Standard enthalpy of formation of 3,4,5-trimethoxybenzoic acid

The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol^-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline and gaseous states at T=298.15 K, Δ_fH_m ^Θ (cr) and Δ_fH_m ^Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol^-1, respectively. The reliability of the results obtained was commented upon and compared with literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Standard molar enthalpy of formation of the ZnO nanosheets

ZnO nanosheets were prepared by a facile microemulsion-mediated hydrothermal route, and were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. As nano ZnO and bulk ZnO possess the same reaction essence, the relationship between standard molar enthalpies of formation of nano ZnO and bulk ZnO was built by designing a novel thermochemical cycle. Combined with microcalorimetry, standard molar enthalpy of formation of the as-prepared ZnO nanosheets at 298.15?K was successfully acquired as (?333.50?±?0.29) kJ?mol^?1. It is an effective strategy for standard molar enthalpies of formation of nano materials through building the relationship with its corresponding bulk material.     

Thermal parameters of undoped and medicines doped calcium hydrogen phosphate dihydrate and magnesium ammonium phosphate hexahydrate crystals

Journal of Thermal Analysis and Calorimetry - In the present study, undoped and medicines doped Calcium Hydrogen Phosphate Dihydrate and Magnesium Ammonium Phosphate Hexahydrate crystals are grown...     

Standard enthalpy of formation of fluorinated graphite CF0.96

The energy of combustion ?? _c U ⁰ of fluorinated graphite CF_0.96 has been determined using an isoperibolic calorimeter with a rotating platinized bomb and the enthalpy of formation ?? _f H ⁰ thereof has been calculated. The enthalpy of the dissociation of the C-F bond has been calculated from the obtained value of ?? _f H⁰(CF_0.96) and compared with analogous values for the previously investigated C₆₀ fullerene fluorides.     

Standard enthalpy of formation of LaCoO3(cr)

An isothermal-jacket calorimeter was used to measure the enthalpies of the reactions of LaCoO₃(cr), LaCl₃(cr), and CoCl₂(cr) with a 2m hydrochloric acid solution. Based on these values and the published data, the standard enthalpy of formation of LaCoO₃(cr) at 298.15 K was calculated (Δ_f H ⁰ = ?1232 ± 6 kJ/mol).     

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.     

Standard enthalpy of formation of fullerene bromide C60Br24

The enthalpy of the combustion of C₆₀Br₂₄ · 2Br₂ has been measured using a rotating-bomb calorimeter as follows: Δ _c H ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (?25986 ± 166) kJ/mol. The result has been used to calculate the standard enthalpy of formation, ΔfH ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (2375 ± 166) kJ/mol. The enthalpies of formation of C₆₀Br₂₄ (cr) and dissociation of the C-Br bond have been estimated. The latter value has been compared with enthalpies for the C-X (X = H, F, Cl, Br) bonds in fullerene derivatives and organic compounds.     

Standard enthalpy of formation of crystalline Ca[NiF6]

The enthalpies of reaction of crystalline Ca[NiF₆](cryst.) with water and a diluted solution of alkali are measured at 298.15 K using an isothermal-shell calorimeter. Based on the obtained values and literature data and using two independent methods, the standard enthalpy of formation of the studied compound is determined (Δ_f H ^○Ca[NiF₆](cryst.) = ?1955 ± 7 kJ/mol).     

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.     

Preparation,Characterization and Standard enthalpy of formation of Sr2CeO4.

Sr₂CeO₄ has been prepared by sol-combustion and co-precipitate routes and the resulting products have been characterized by XRD analysis. The molar enthalpies of solution of Sr₂CeO₄(s), Sr(NO₃)₂(s) and Ce(NO₃)₃·6H₂O(s) in 0.150 dm^–3 of (4.41 mol dm–3 H₂O₂+4.23 mol dm^–3 of HNO₃) solvent as well as the molar enthalpies of solution of Sr₂CeO₄(s), SrCl₂(s) and CeCl₃(s) in 0.150 dm³ of (1.47 mol dm^–3 H₂O₂+3.05 mol dm^–3 of HClO₄) solvent have been measured using an isoperibol type calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of Sr₂CeO₄ has been derived to be –2277.3±3.1 kJ mol^–1 at 298.15 K. This is the first reported thermodynamic data on this compound.     

Standard molar enthalpy of formation of 1-benzosuberone: An experimental and computational study

The energetics of 1-benzosuberone was studied by a combination of calorimetric techniques and computational calculations.The standard (p° = 0.1 MPa) molar enthalpy of formation of 1-benzosuberone, in the liquid phase, was derived from the massic energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T = 298.15 K, was measured by Calvet microcalorimetry. From these two parameters the standard (p° = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, was derived: ?(96.1 ± 3.4) kJ · mol^?1. The G3(MP2)//B3LYP composite method and appropriate reactions were used to computationally calculate the standard molar enthalpy of formation of 1-benzosuberone, in the gaseous phase, at T = 298.15 K. The computational results are in very good agreement with the experimental value.