Molar Enthalpies Of Formation Research Articles

Synthesis, characterization, and calorimetric investigation of ternary lanthanide complexes with benzoic acid and 2-phenylimidazo[4,5-f]1,10-phenanthroline

A series of solid ternary lanthanide complexes with the general formula Ln(BA)3(PIP) (Ln = La–Lu, except Pm) were prepared with hydrated lanthanide chloride, benzoic acid (BA), and 2-phenylimidazo[4,5-f]1,10-phenanthroline (PIP). These obtained complexes were characterized by means of elemental analysis, EDTA volumetric analysis, IR spectroscopy, X-ray powder diffraction, and mass spectroscopy. The thermal decomposition mechanism of all complexes in the solid state was explored using TG–DTG techniques under dynamic flow of air atmosphere. Moreover, the constant-volume combustion energies, ∆c U, of the complexes were determined by a precise rotating-bomb calorimeter (RBC-type II) at 298.15 K. Their standard molar enthalpies of combustion, $$ \Delta _{\text{c}} H_{\text{m}}^{\uptheta} $$ , and standard molar enthalpies of formation, $$ \Delta_{\text{f}} H_{\text{m}}^{\uptheta} $$ , were calculated.

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.

Synthesis, structure and thermochemical study of a cobalt energetic coordination compound incorporating 3,5-diamino-1,2,4-triazole and pyridine-2,6-dicarboxylic acid

An energetic coordination compound [Co2(C2H5N5)2(C7H3NO4)2(H2O)2]·2H2O (Hdatrz(C2H5N5)=3,5-diamino-1,2,4-triazole, H2pda(C7H5NO4)=pyridine-2,6-dicarboxylic acid) has been synthesized and characterized by elemental analysis, chemical analysis, IR spectroscopy, single-crystal X-ray diffraction and thermal analysis. X-ray diffraction analysis confirmed that the compound possessed a di-nuclear unit and featured a 3D super-molecular structure. Furthermore, a reasonable thermochemical cycle was designed based on the preparation reaction of the compound and the standard molar enthalpy of dissolution of reactants and products was measured by the RD496-2000 calorimeter. Finally, the standard molar enthalpy of formation of the compound was determined to be −(2475.0±3.1)kJ·mol−1 in accordance with Hess’s law. In addition, the specific heat capacity of the compound at T=298.15K was determined to be (1.13±0.02)J·K−1·g−1 by RD496-2000 calorimeter.

Thermodynamic and conformational study of proline stereoisomers.

Amino acids play fundamental roles both as building blocks of proteins and as intermediates in metabolism. Proline, one of the 20 natural amino acids, has a primordial function in enzymes, peptide hormones, and proteins. The energetic characterization of these molecules provides information concerning stability and reactivity and has great importance in understanding the activity and behavior of larger molecules containing these structures as fragments. In the present work, parallel experimental and computational studies have been performed. The experimental studies have been based on calorimetric and effusion techniques, from which the enthalpy of formation in the crystalline phase and the enthalpy of sublimation of the sterioisomers L-, D-, and the DL-mixture of proline have been derived. Additionally, vapor pressure measurements have also enabled the determination of the entropies and Gibbs energies of sublimation, at T = 298.15 K. From the former results, the experimental standard (p(o) = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of L-proline, D-proline, and DL-proline have been calculated as -388.6 ± 2.3, -391.9 ± 2.0, and -391.5 ± 2.4 kJ·mol(-1), respectively. A computational study at the G3 and G4 levels has been carried out. Conformational analysis has been done and the enthalpy of formation of proline as well as other intrinsic properties such as acidity, basicity, adiabatic ionization enthalpy, electron and proton affinities, and bond dissociation enthalpies have been calculated. There is a very good agreement between calculated and experimental values, when they are available.

Processes on the Thermodynamic Properties of Lithium Borates

In this paper, the thermodynamic properties including the standard molar enthalpies of formation, the standard molar entropies of formation and the standard molar Gibbs free energy of formation of hydrated lithium borates and the water vapor pressures, the osmotic coefficients, the enthalpy of dilution, the molar heat capacity of aqueous lithium borate solution systems were summarized and the new trend in the future was also pointed out.

Gas phase enthalpies of formation of nitrobenzamides using combustion calorimetry and thermal analysis

The standard molar energies of combustion of 2-nitrobenzamide, 3-nitrobenzamide and 4-nitrobenzamide were determined with an isoperibolic, static-bomb, combustion calorimeter. From the combustion results, the standard molar enthalpies of combustion and formation for these compounds in the condensed phase at T=298.15K were derived. Subsequently, to determine the enthalpies of sublimation, the vapour pressure data as a function of the temperature for the compounds under investigation were estimated using thermogravimetry by applying Langmuir’s equation, and the enthalpies of vaporisation were derived. Standard enthalpies of fusion were measured by differential scanning calorimetry then added to those of vaporisation to obtain reliable results for the enthalpy of sublimation. From the combustion and sublimation data, the gas phase enthalpies of formation were determined to be (−138.9±3.5)kJ·mol−1, (−122.9±2.9)kJ·mol−1 and (−108.5±3.7)kJ·mol−1 for the ortho, meta and para isomers of nitrobenzamide, respectively. The meaning of these results with regard to the enthalpic stability of these molecular structures is discussed herein.

Crystal structure and thermochemical properties of a novel coordination compound sodium pyruvate C3H3O3Na(s)

A novel coordination compound sodium pyruvate C3H3O3Na(s) is synthesised by a liquid phase reaction. The compound has an obvious bioactivity and can be used as the biological carbon source and the chemical identification of primary and secondary alcohols. It can be also used to determinate transaminase. Elemental analysis and X-ray crystallography are used to characterise the composition and crystal structure of the compound. Single crystal X-ray analysis reveals that the compound is formed by one CH3COCOO− anion and one Na+ cation. An obvious feature of the crystal structure is the formation of the five-membered chelate ring by the coordination of O1 of carboxylate and O3 of keto form with Na+ cation, and it is good for the stability of the compound in structure. The lattice potential energy and ionic volume of the anion are obtained from crystallographic data. In accordance with Hess’ law, a reasonable thermochemical cycle is designed according to the practical synthesis reaction of the compound and the standard molar enthalpy of formation of the compound is calculated as an important physical quantity in chemical thermodynamics by use of an isoperibol solution-reaction calorimeter. Molar enthalpies of dissolution of the compound at various molalities are measured at T=298.15K in the double-distilled water. According to Pitzer’s electrolyte solution theory, molar enthalpy of dissolution of the title compound at infinite dilution is calculated to be ΔsHm∞=(19.81±0.69)kJ·mol−1. The values of relative apparent molar enthalpies (ΦL) and relative partial molar enthalpies of the solvent (L¯1) and the compound (L¯2) at different concentrations m/(mol·kg−1) are derived from the experimental values of the enthalpies of dissolution of the compound.

Calorimetric study of bromoacetophenone isomers

The standard (po=0.1MPa) molar enthalpies of formation of 2-, 2′-, 3′- and 4′-bromoacetophenones were derived from the standard molar energies of combustion in oxygen, to yield CO2 (g) and HBr·600H2O (l) at T=298.15K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies associated with phase transitions of the isomers studied at T=298.15K, were obtained by high temperature Calvet microcalorimetry. The standard (po=0.1MPa) molar enthalpies of formation of all the bromoacetophenone isomers in the gaseous phase at T=298.15K were derived from the experimental results. The gas-phase enthalpies of formation were also estimated by the empirical scheme developed by Cox and the values obtained were compared with the experimental ones. The results are interpreted in terms of the energetic increments for the introduction of the substituents in the benzene ring.

Standard molar enthalpy of formation of Ce2Zr2O8

Cerium zirconate, Ce2Zr2O8(s), is an interesting material having potential applications such as matrix for immobilization of nuclear waste, component in the inert matrix fuel, oxygen storage capacitor and catalyst for chemical reactions, etc. Long term stability of the compound under reactive conditions is essential for its utilization. Thermodynamics plays an important role in predicting the stability of the material. The present paper describes determination of the standard molar enthalpy of formation (ΔfH°298) of Ce2Zr2O8(s) employing a high temperature solution calorimeter. The enthalpies of dissolution of CeO2(s), ZrO2(s), Ce2Zr2O8(s) in liquid Na2O+MoO3 solvent (3:4M ratio) at 986K were measured employing a Calvet Calorimeter. The standard molar enthalpy of formation of the compound at 298K (ΔfH°298) was calculated by combining the experimentally determined values of the reaction enthalpies with the auxiliary data from the literature. The standard molar enthalpy of formation (ΔfH°298) of Ce2Zr2O8 was found to be –(4344.0±4.0) kJmol−1. Ce2Zr2O8(s) is a metastable compound, which decomposes to Ce-rich ZrO2 and Zr-rich CeO2 fluorite-type phases, when heated above 1673K. The extent of metastability of Ce2Zr2O8 compared to its stable decomposed products has been determined.

Crystal structure and thermochemistry of a novel coordination compound 2-pyrazine carboxylate sodium

2-Pyrazine carboxylate sodium Na2(PCA)2(s) was synthesized. X-ray crystallography was applied to characterize its crystal structure. Chemical and elemental analyses were used to determine its composition and purity. A precise automatic adiabatic calorimeter was used to measure heat capacities in the temperature range from 78 to 400 K. A polynomial equation of experimental molar heat capacities as a function of the temperature was obtained. The smoothed molar heat capacities and thermodynamic functions of the compound were calculated. The standard molar enthalpies of dissolution for the reactants and products of the synthesis reaction in the selected solvent were measured by an isoperibol solution-reaction calorimeter. The enthalpy change of the reaction was determined to be (1.70 ± 0.82) kJ mol−1, and the standard molar enthalpy of formation of the complex was derived to be −(1,108.70 ± 2.51) kJ mol−1. In addition, the reliability of the designed thermochemical cycle was verified by UV–Vis spectra.

Standard partial molar heat capacities and enthalpies of formation of aqueous aluminate under hydrothermal conditions from integral heat of solution measurements

Heats of solution of sodium aluminum oxide, NaAlO2(s), were measured in aqueous sodium hydroxide solutions using a Tian–Calvet heat-flow calorimeter (Setaram, Model C80) with high pressure “batch cells” made of hastelloy C-276, at five temperatures from (373.15 to 523.15)K, steam saturation pressure, and concentrations from (0.02 to 0.09)mol·kg−1. Standard molar enthalpies of solution, ΔsolnH∘, and relative standard molar enthalpies, [H∘(T)−H∘(298.15K)], of NaAl(OH)4(aq) were determined from the measured heats of solution. The results were fitted with the “density” model. The temperature dependence of ΔsolnH∘ from the model yielded the standard molar heat capacities of reaction, ΔsolnCp∘, from which standard partial molar heat capacities for aqueous aluminate, Cp∘[A1(OH)4−,aq], were calculated. Standard partial molar enthalpies of formation, ΔfH∘, and entropies, S∘, of A1(OH)4−(aq) were also determined. The values for Cp∘[A1(OH)4−,aq] agree with literature data determined up to T=413K from enthalpy of solution and heat capacity measurements to within the combined experimental uncertainties. They are consistent with differential heat capacity measurements up to T=573K from Schrödle et al. (2010) [29] using the same calorimeter, but this method has the advantage that measurements could be made at much lower concentrations in the presence of an excess concentration of ligand. To our knowledge, these are the first standard partial molar heat capacities measured under hydrothermal conditions by the integral heat of solution method in a commercial calorimeter to be reported in the literature.

Thermochemical investigation of YBa2Cu3O7−δ superconductor doped by lutetium

The synthesis of Y0.72Lu0.28Ba2Cu3O6.91 has been performed by solid-state reaction from Y2O3, Lu2O3, BaCO3 and CuO. The X-ray measurements confirmed the orthorhombic structure (space group is Pmmm). For the first time the standard molar enthalpy of formation of Y0.72Lu0.28Ba2Cu3O6.91 has been determined by solution calorimetry combining the enthalpies of dissolution of Y0.72Lu0.28Ba2Cu3O6.91 in 2M HCl and literature data. It is found out that at room temperature this complex oxide is thermodynamically stable with respect to a decomposition into binary oxides or a mixture of individual phases (YBa2Cu3O6.91 and LuBa2Cu3O6.91). It could be established that substitution of Lu increases the stability of the Y123 phase.

High-energy-density materials with remarkable thermostability and insensitivity: syntheses, structures and physicochemical properties of Pb(ii) compounds with 3-(tetrazol-5-yl) triazole

Two energetic compounds, [Pb(Htztr)2(H2O)]n (1) and [Pb(H2tztr)(O)]n (2), were synthesized and then structurally characterized (N% = 39.4% for 1, N% = 27.2% for 2), where Htztr represents 3-(tetrazol-5-yl)triazole. Structural analysis revealed that both compounds have reticular two-dimensional structures. Remarkably, thermogravimetric measurements demonstrated that the compounds possess excellent thermostabilities with high decomposition temperatures up to 340 °C for (1) and 318 °C for (2). The kinetic parameters of exothermic processes were studied by the Kissinger's and Ozawa–Doyle's methods. The standard molar enthalpies of formation were obtained from the determination of constant-volume combustion energies. The calculated detonation properties showed that compound (1) can be used as a potential explosive. Sensitivity tests revealed that the compounds are extremely insensitive. In addition, two compounds were examined for use as additives to promote the thermal decomposition of ammonium perchlorate and hexahydro-1,3,5-trinitro-1,3,5-triazine.

Molar heat capacities and standard molar enthalpy of formation of pyrimethanil butanedioic salt

A noval anilino-pyrimidine fungicide, pyrimethanil butanedioic salt (C28H32N6O4), was synthesized by a chemical reaction of pyrimethanil and butanedioic acid. The low-temperature heat capacities of the compound were measured with an adiabatic calorimeter from 80 to 380 K. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity fitted curve. The thermal stability of the compound was investigated by TG and DSC. The TG curve shows that pyrimethanil butanedioic salt starts to sublimate at 455.1 K and totally changes into vapor when the temperature reaches 542.5 K with the maximal speed of weight loss at 536.8 K. The melting point, the molar enthalpy (Δfus H m), and entropy (Δfus S m) of fusion were determined from its DSC curves. The constant-volume energy of combustion (Δc U m) of pyrimethanil butanedioic salt was measured by an isoperibol oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpy of formation was derived and determined to be Δf H m o (pyrimethanil butanedioic salt)=−285.4 ± 5.5 kJ mol−1.

Thermodynamic properties of the methyl esters of p-hydroxy and p-methoxy benzoic acids

The vapor pressures of crystalline and liquid phases of methyl p-hydroxybenzoate and of methyl p-methoxybenzoate were measured over the temperature ranges (338.9 to 423.7)K and (292.0 to 355.7)K respectively, using a static method based on diaphragm capacitance gauges. The vapor pressures of the crystalline phase of the former compound were also measured in the temperature range (323.1 to 345.2)K using a Knudsen mass-loss effusion technique. The results enabled the determination of the standard molar enthalpies, entropies and Gibbs free energies of sublimation and of vaporization, at T=298.15K, as well as phase diagram representations of the (p,T) experimental data, including the triple point. The temperatures and molar enthalpies of fusion of both compounds were determined using differential scanning calorimetry and were compared with the results indirectly derived from the vapor pressure measurements. The standard (p°=105Pa) molar enthalpies of formation, in the crystalline phase, at T=298.15K, of the compounds studied were derived from their standard massic energies of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpies of formation, in the gaseous phase at T=298.15K, were calculated and compared with the values estimated by employing quantum chemical computational calculations. A good agreement between experimental and theoretical results is observed. To analyze the thermodynamic stability of the two compounds studied, the standard Gibbs free energies of formation in crystalline and gaseous phases were undertaken. The standard molar enthalpies of formation of the title compounds were also estimated from two different computational approaches using density functional theory-based B3LYP and the multilevel G3 methodologies.

Thermochemistry of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids: Experimental and computational study

This paper reports an experimental and computational thermochemical study on two barbituric acid derivatives, viz. 1,3-diethylbarbituric acid and 1,3-diethyl-2-thiobarbituric acid. Values of standard molar enthalpies of formation in the gas phase at T=298.15K have been derived from experiment. Energies of combustion were measured by the static bomb combustion calorimetry in the case of 1,3-diethylbarbituric acid, and the rotating-bomb combustion calorimetry in the case of 1,3-diethyl-2-thiobarbituric acid. From the combustion energies, standard molar enthalpies of formation in the crystalline state at T=298.15K were calculated. The enthalpy of vaporization of 1,3-diethylbarbituric acid and enthalpy of sublimation of 1,3-diethyl-2-thiobarbituric acid were determined using the transpiration method. Combining calorimetric and transpiration results, values of −(611.9±2.0)kJ·mol−1 and −(343.8±2.2)kJ·mol−1 for the gas-phase enthalpies of formation at T=298.15K of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids, respectively, were derived. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular structure of the compounds has been carried out. Calculated enthalpies of formation were in very good agreement with the experimental values.

Structural and energetic characterization of the tautomers 2-benzothiazolinone and 2-hydroxybenzothiazole

This work reports an experimental and computational thermochemical study for 2-benzothiazolinone. The standard (p°=0.1MPa) molar energy of combustion of this compound was measured by rotating bomb combustion calorimetry. The standard molar enthalpy of the corresponding transition from crystalline to gaseous phases, at T=298.15K, was obtained from high temperature Calvet microcalorimetry measurements. The experimental results enable the calculation of the standard molar enthalpy of formation of the compound, in the gaseous state, at T=298.15K.The gas-phase enthalpies of formation of the title compounds, 2-benzothiazolinone and its enol form 2-hydroxybenzothiazole, were estimated computationally from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. The computed value for the keto form compares very well with the experimental result obtained in this work. The hydroxy↔oxo tautomerism of the title compounds was explored in this work as it may be relevant to their ability to occur as different polymorphic forms.

Synthesis, thermochemical and thermokinetic studies on the mononuclear copper Valen Schiff base complex

A mononuclear salen-type complex [Cu( vanen )(H 2 O)] was synthesized from the ligand [H 2 vanen = N , N - ethylene-bis(3-methoxysalicylideneimine)] and Cu(OAc) 2 ·H 2 O. Based on Hess law, a reasonable thermochemical cycle was designed. According to the cycle, the standard molar enthalpies of dissolution of samples in the calorimetric solvent of DMF ( N , N -dimethylformamide) were determined, respectively. The standard molar enthalpy change of the coordination reaction (Δ r H m θ ) was calculated to be -(16.61 ± 0.54) kJ/mol. Combined with some relevant literature data, the standard molar enthalpy of formation (Δ f H m θ ) of the complex was obtained to be -(756.5 ± 2.4) kJ/mol. At the temperature of 32 ℃, the metabolic thermogenetic curves of S. pombe under the influence of the complex with different concentration were determined by using a TAM air isothermal calorimeter. The relationships of the concentration of the complex with the microbial growth rate constant ( k ) of S. pombe , inhibition ratio (I), the half inhibition concentration (IC 50 ), the maximum heat output power ( P max ) and the time it took ( t max ) were analyzed. The results indicated that the complex possessed the Hormesis effect, which promoted the growth of S. pombe at lower concentration, but inhibited the growth at higher concentration.

Standard Molar Formation Enthalpy of NH4Fe(HPO4)2

Ammonium-iron(III) bis(hydrogenphosphate) was synthesized via solid-state reaction at low temperature and characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscope. Standard molar enthalpy of formation was determined by an isoperibol solution calorimeter at 298.15K. The results show that the obtained product is NH4Fe(HPO4)2 with shape of Lamellar particles. According to Hess's law, a new thermochemical cycle was designed, and the standard enthalpy of formation of the titled complex at 298.15K is: ΔfHmφ[(NH4)Fe(HPO4)2 (s), 298.15K] = −2641.52 ±0.06 kJ·mol−1.

Thermochemistry of 6-propyl-2-thiouracil: An experimental and computational study

The standard (po = 0.1 MPa) molar enthalpy of formation of 6-propyl-2-thiouracil was derived from its standard molar energy of combustion, in oxygen, to yield CO2 (g), N2 (g) and H2SO4·115H2O (l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressures as function of temperature were measured by the Knudsen effusion technique and the standard molar enthalpy of sublimation, ΔcrgHmo, at T = 298.15 K, was derived by the Clausius–Clapeyron equation. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K: −(142.5 ± 1.9) kJ mol−1. This value was compared with estimates obtained from very accurate computational calculations using the G3 and G4 composite methods.