Molar Enthalpies Of Formation Research Articles

Thermochemistry of amino-1,2,4-triazole derivatives

AbstractThe present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1H-1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4H-1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

Thermodynamic insights of ternary compounds of NiO - V2O5 system

We present the first experimental investigation on thermochemical stability of three ternary nickel vanadates, namely, NiV2O6(s), Ni2V2O7(s) and Ni3V2O8(s) in the NiO-V2O5 system. The standard molar entropies of formation of the compounds were determined by low temperature heat capacity measurements from 2 to 300 K using relaxation calorimetry. The standard molar enthalpy of formation and molar heat capacities were determined employing high temperature oxide melt solution calorimetry in conjunction with differential scanning calorimetry. Using the experimentally obtained thermochemical data, the standard molar Gibbs energy of formation of these compounds were derived and the corresponding expressions are given as follows:∆Gf,m°<NiV2O6>±1.4kJmol−1=−1839.4+0.5132(T/K)(T:298.15−1000K)∆Gf,m°<Ni2V2O7>±1.4kJmol−1=−2101.8+0.5971(T/K)(T:298.15−1000K)∆Gf,m°<Ni3V2O8>±3.2kJmol−1=−2360.5+0.6538(T/K)(T:298.15−1000K)

Construction of energetic metal-organic frameworks based on 5-aminotetrazole

Metal-Organic Frameworks (MOFs) have recently gained prominence as a novel class of energetic materials, owing to their systematic design and the ability to fine-tune properties such as energy content, sensitivity, and thermal stability. In this study, two new MOFs namely Cd(5-AT)3NH2(CH3)2+(1) and Zn(5-AT)(AMP) (2) (5-HAT = 5-aminotetrazole) were prepared under solvothermal conditions using 5-aminotetrazole as the high-nitrogen energetic ligand. X-ray single crystal diffraction analysis revealed that compound 1 possess an ABX3-type perovskite-like structure, whereas compound 2 forms a two-dimensional layer. The high thermal stability of both compounds were confirmed through thermogravimetry (TG) and differential scanning calorimetry (DSC). Their constant-volume combustion heat (ΔcU) was first determined by oxygen-bomb calorimetry and then the standard molar enthalpy of formation (ΔfHo) was calculated. Furthermore, both compounds demonstrated great detonation properties and low sensitivity, showing their potential application as new explosive materials (EMs).

Experimental Determination of the Standard Enthalpy of Formation of Trimellitic Acid and Its Prediction by Supervised Learning.

The standard molar enthalpy of formation for trimellitic acid (TMAc) in the crystalline phase at 298.15 K, ΔfHm°(cr), was calculated experimentally from the enthalpy of combustion through combustion calorimetry experiments. Likewise, the standard molar enthalpy of sublimation was determined from the standard molar enthalpy of fusion and from the standard molar enthalpy of vaporization from differential scanning calorimetry and thermogravimetry, respectively. Subsequently, the standard molar enthalpies of formation in the gas-phase at 298.15 K, ΔfHm°(g), were calculated. The enthalpies of formation for TMAc, hemimellitic, and trimesic acids were predicted using multiple linear regression (MLR) with a nonreplacement evaluation technique. MLR was applied to the data set that allowed estimating these thermochemical properties with an R2 greater than 0.99. This model was used to compare the predicted and experimental results for benzene carboxylic acids.

3,5‐dinitro‐N2,N6‐bis(2,4,6‐trinitrophenyl)pyrazine‐2,6‐diamine (ZXC‐71): Thermally stable explosives with outstanding properties

AbstractSingle‐compound heat‐resistant explosives are an important class of high‐energy compounds with excellent thermal stability. In this paper, a novel thermally stable explosive 3,5‐dinitro‐N2,N6‐bis(2,4,6‐trinitrophenyl)pyrazine‐2,6‐diamine (ZXC‐71) is reported. The commercially available 2,6‐dichloropyrazine was used as raw materials to prepare this compound with a straightforward method. The crystalline structure of ZXC‐71 was determined by single‐crystal X‐ray diffraction. From the calculated standard molar enthalpy of formation and the measured density, the Chapman–Jouguet detonation properties were predicted. The detonation velocity (D), detonation pressure (P), and density (ρ) of ZXC‐71 are 8608 m s−1, 29.8 GPa, and 1.86 g cm−3, respectively. ZXC‐71 also exhibits remarkable impact sensitivity (FS=22 J).

7-Methoxy-4-methylcoumarin: Standard Molar Enthalpy of Formation Prediction in the Gas Phase Using Machine Learning and Its Comparison to the Experimental Data.

Experimentally, the standard molar enthalpy of formation in the crystalline phase at 298.15 K, ΔfHm°(cr) for 7-methoxy-4-methylcoumarin (7M4MC) was calculated by traditional linear regression, which was obtained by combustion calorimetry. Similarly, the standard molar enthalpy of sublimation was determined through the standard molar enthalpy of fusion and by the standard molar enthalpy of vaporization, from differential scanning calorimetry and thermogravimetry, respectively; lately using these results, the standard molar enthalpy of formation in the gas phase was calculated at 298.15 K, ΔfHm°(g). In addition ML was used to predict the standard molar enthalpy of formation in the gas phase for the 7M4MC, constructing an experimental data set containing three kinds of functional groups: esters, coumarins, and aromatic compounds. The procedure was performed by using multiple linear regression algorithms and stochastic gradient descent with a R2 of 0.99. The obtained models were used to compare those predicted values versus experimental for coumarins, resulting in an average error rate of 9.0%. Likewise, four homodesmic reactions were proposed and predicted with the multiple linear regression algorithm of ML obtaining good results.

Synthesis and thermodynamic properties of 4ZnO·B2O3·H2O with three different morphologies

Polycrystalline 4ZnO·B2O3·H2O with flower-like, spherical-like and sheet-like morphologies have been synthesized and characterized by XRD, TG–DSC, SEM and TEM. The molar enthalpies of solution of 4ZnO·B2O3·H2O with different morphologies in 1 mol L−1 HCl(aq) were measured. With the incorporation of the previously determined enthalpy of solution of H3BO3 in 1 mol L−1 HCl(aq), the enthalpy of solution of ZnO in (HCl + H3BO3)(aq) and the standard molar enthalpies of formation of ZnO(s), H3BO3(s) and H2O(l), the standard molar enthalpies of formation of 4ZnO·B2O3·H2O with flower-like, spherical-like, and sheet-like morphologies were calculated to be -(3033.91 ± 2.03), -(3030.91 ± 2.03) and -(3025.94 ± 2.04) kJ·mol−1, respectively.

Zn-Mo-O system: Insights into the thermodynamic stability and applicability in lithium ion batteries

A detailed experimental investigation on the thermochemical stability of Zn2Mo3O8(s) in the Zn-Mo-O system was reported for the first time using high temperature oxide melt solution calorimetry in conjunction with solid oxide based electrochemical measurements. The temperature dependence of molar heat capacity of this compound was determined employing thermal relaxation calorimetry and differential scanning calorimetry. The values of standard molar enthalpy of formation (∆fH298.15°), standard molar entropy (S298.15°), molar heat capacity (Cp) and Debye temperature (θD) for Zn2Mo3O8(s) were determined for the first time in this study. The present study also focuses on the investigation of electrochemical performance of α-ZnMoO4(s) for lithium ion battery applications which demonstrated the effective utilization of this compound as anode material due to its remarkable cycling stability and rate capability.

A comprehensive investigation on CdO-SnO2 system: Structure, thermal expansion and energetics

An extensive investigation into the thermochemical stability of two ternary oxides, ilmenite-type CdSnO3(s) and orthorhombic Cd2SnO4(s), in the Cd-Sn-O system was reported for the first time using high temperature oxide melt solution calorimetry in conjunction with differential scanning calorimetry and thermal relaxation calorimetry. The values of standard molar enthalpy of formation (∆fH298.15°), standard molar entropy (S298.15°), molar heat capacity and Debye temperature (θD) for ilmenite-type CdSnO3(s) and orthorhombic Cd2SnO4(s) were determined. Using the experimentally obtained thermochemical data, the standard molar Gibbs energy of formation of these compounds were derived and the corresponding expressions are given as follows:∆fGm°<CdSnO3>±1.3kJmol−1=−847.9+0.2781(T/K)(T:298.15−1000K)∆fGm°<Cd2SnO4>±3.6kJmol−1=−1138.1+0.3831(T/K)(T:298.15−1000K)Moreover, high temperature XRD experiments were conducted to evaluate their thermal expansion behaviour as well as for the in-situ identification of phase evolution resulting from decomposition of cadmium stannates.

Standard molar enthalpies of formation of 3-methylglutaric and 3,3-dimethylglutaric anhydrides

In this research, both the standard molar enthalpy of formation in the crystalline phase and in the gas phase of 3-methylglutaric anhydride was calculated from experimental data. The temperature and enthalpy of fusion, as well as the molar heat capacity in solid phase was calculated by differential scanning calorimetry; the molar enthalpy of sublimation at 298.15 K by the Knudsen effusion method, the molar enthalpy of vaporization at 298.15 K by thermogravimetric analysis, and the standard massic combustion energy by combustion adiabatic calorimetry. Since 3,3-dimethylglutaric anhydride presented crystal transitions (with endothermic points at 352.76 K, 356.98 K and 397.15 K), some of its thermochemical properties were estimated from the functional group-contribution methods proposed by Benson, Gani and Naef and from application of Machine Learning based models.

Pyrolysis behavior, properties and mechanism of high-energy oxidizer 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate

To evaluate the thermal properties and promote the application of 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate (BHDBT), thermal behavior of BHDBT was studied systematically using differential scanning calorimetry (DSC), thermogravimetric analysis (TG/DTG) and thermogravimetric-infrared-mass spectrometry (TG-IR-MS) techniques. The results show that the thermal behavior of BHDBT presents two stages, one is an obvious endothermic melting process, the other is a big exothermic decomposition process with mass loss of about 81 %, and the peak temperatures (Tp) of two processes are 86.5 °C and 186.9 °C at the heating rate of 10 °C min−1, respectively. In high-pressure sealed crucible, BHDBT presents similar thermal behavior to that in common open crucible. Non-isothermal decomposition kinetics equation of BHDBT was obtained, and the possible thermal decomposition mechanism for BHDBT was proposed based on the main gas-phase products, including H2O, HCN, CO, CO2, NO, N2O and NO2, which are proved by TG-IR-MS testing results. Finally, the combustion heat and standard molar enthalpy of formation of BHDBT were measured and calculated. All results will provide a theoretical support for the application of BHDBT.

Equilibria of the ternary systems CsBr–LnBr3 (Ln = Gd, Dy)–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O at T = 298.15 K and standard molar enthalpies of formation for new compounds

As part of a series of studies, this paper reports experimental phase equilibrium data for CsBr–GdBr3–H2O, CsBr–DyBr3–H2O and CsBr–GdBr3–HBr (∼12.1 mass %)–H2O systems at T = 298.15 K. The phase diagrams were constructed based on the measured data. In the phase diagrams of the ternary system CsBr–GdBr3–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O,there are all two invariant points, and three crystallization regions corresponding to CsBr, Cs3GdBr6·10H2O, and GdBr3·6H2O, respectively.There are two invariant points and three crystallization regions corresponding to CsBr, Cs3Dy2Br9·16H2O and DyBr3·6H2Oin the system CsBr–DyBr3–H2O.The experimental solubility values of gadolinium bromide and dysprosium bromide at 298.15 K were 65.42 mass % and 65.94 mass %. The compounds Cs3GdBr6·10H2O and Cs3Dy2Br9·16H2O are incongruently soluble in water or a medium of ∼ 12.1 mass % HBr, and were characterized by XRD and TG-DTG techniques. The standard molar enthalpies of solution for Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were obtainedby means of microcalorimetric measurement, the values found for standard molar enthalpies of formation of Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were – (5104.8 ± 3.2) kJ·mol−1, – (7827.3 ± 3.6) kJ·mol−1, – (2726.0 ± 2.7) kJ·mol−1 and – (2734.5 ± 3.3) kJ·mol−1, respectively.

Thermodynamic properties of benzotriazole derivatives: An experimental and computational study

A thermochemical study of 5-methyl-1H-benzotriazole and 5,6-dimethyl-1H-benzotriazole was carried out experimentally using calorimetric techniques and an effusion method. Parallel to that, a computational methodology was also applied. The massic energies of combustion and the enthalpies of sublimation were determined from static bomb combustion calorimetry and Knudsen mass-loss effusion method and/or high-temperature Calvet microcalorimetry, respectively. From these experimental data, the standard molar enthalpies of formation of the two benzotriazoles in the gaseous phase were derived. Additionally, the gas-phase enthalpies of formation of these benzotriazoles and other two methylated derivatives were calculated using the G3(MP2)//B3LYP level of theory. The data obtained allowed the study of the energetic effects associated with the presence of a methyl group in the benzotriazole structure and their comparison with identical effects in homocyclic molecules, namely benzene and naphthalene. The Gibbs energies of formation of the compounds in the crystalline and gaseous phases were also determined to assess their thermodynamic stability.

Dipropargyl ethers possessing nitramine units

The syntheses and characterization of novel propargyl ethers of N-(hydroxymethyl)nitramines that contain from one to four nitramine units are reported. All nitramine-functionalized ethers were well characterized by IR and multinuclear NMR spectroscopy as well as CHN analysis, and the X-ray crystal structures of two of them are described. For ethers bearing two or three nitramine units, the standard molar enthalpies of formation at 298.15 K were determined from the experimental standard molar energies of combustion in oxygen measured by static bomb combustion calorimetry

Stabilizing Effect of a 4c/6e Hypervalent Bond in Dinitrodiphenyl Disulfides and Their Thermochemical Properties: Experimental and Computational Approach.

Thermochemical properties and intramolecular interactions of 2,2'-dinitrodiphenyl disulfide (2DNDPDS) and 4,4'-dinitrodiphenyl disulfide (4DNDPDS) were determined and analyzed. Their standard molar formation enthalpies in the gas phase (ΔfHm°(g)'s) were experimentally determined; theoretically, they were computed using the G4 composite method and atomization reactions. Specifically, ΔfHm°(g)'s were obtained by combining formation enthalpies in the condensed phase and enthalpies of phase change. Formation enthalpies in the condensed phase were determined experimentally through combustion energies, which in turn were found by means of a rotatory bomb combustion calorimeter. Sublimation enthalpies were derived from thermogravimetric experiments, measuring the rate of mass loss and using Langmuir and Clausius-Clapeyron equations. Fusion enthalpies and heat capacities of the solid and liquid phases were measured as functions of temperature by differential scanning calorimetry, and the heat capacities of the gas phase were calculated via molecular orbital calculations. Theoretical and experimental ΔfHm°(g)'s differed by <5.5kJ·mol-1, and isomerization enthalpies are discussed. In addition, using theoretical tools [natural bond orbitals (NBO) and quantum theory of atoms in molecules (QTAIM)], intramolecular interactions were analyzed. An uncommon hypervalent four-center six-electron interaction of type O···S-S···O was found in 2DNDPDS. This hypervalent interaction, in addition to the extent of conjugation between the aryl and NO2 moieties and the formation of intramolecular C-H···S hydrogen bonds, counteracts the repulsion caused by steric repulsions. Hydrogen bonding was confirmed through geometric parameters as well as QTAIM.

Machine learning-driven QSAR models for predicting the mixture toxicity of nanoparticles

Research on theoretical prediction methods for the mixture toxicity of engineered nanoparticles (ENPs) faces significant challenges. The application of in silico methods based on machine learning is emerging as an effective strategy to address the toxicity prediction of chemical mixtures. Herein, we combined toxicity data generated in our lab with experimental data reported in the literature to predict the combined toxicity of seven metallic ENPs for Escherichia coli at different mixing ratios (22 binary combinations). We thereafter applied two machine learning (ML) techniques, support vector machine (SVM) and neural network (NN), and compared the differences in the ability to predict the combined toxicity by means of the ML-based methods and two component-based mixture models: independent action and concentration addition. Among 72 developed quantitative structure–activity relationship (QSAR) models by the ML methods, two SVM-QSAR models and two NN-QSAR models showed good performance. Moreover, an NN-based QSAR model combined with two molecular descriptors, namely enthalpy of formation of a gaseous cation and metal oxide standard molar enthalpy of formation, showed the best predictive power for the internal dataset (R2test = 0.911, adjusted R2test = 0.733, RMSEtest = 0.091, and MAEtest = 0.067) and for the combination of internal and external datasets (R2test = 0.908, adjusted R2test = 0.871, RMSEtest = 0.255, and MAEtest = 0.181). In addition, the developed QSAR models performed better than the component-based models. The estimation of the applicability domain of the selected QSAR models showed that all the binary mixtures in training and test sets were in the applicability domain. This study approach could provide a methodological and theoretical basis for the ecological risk assessment of mixtures of ENPs.

On the Enthalpy of Formation and Enthalpy of Sublimation of Dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50)

AbstractThe thermodynamic characterization of dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50) was reinvestigated. Although TKX‐50 is one of the most promising new‐generation energetic materials, contradictory reports are found in the literature with regard to its solid enthalpy of formation. The standard (po=105 Pa) molar enthalpy of formation of crystalline TKX‐50, (175.3±1.9) kJ ⋅ mol−1, was determined experimentally based on the measured standard massic energy of combustion, determined through static‐bomb combustion calorimetry. Additionally, the standard molar enthalpy of sublimation of TKX‐50, at T=298.15 K, (165.0±2.4) kJ ⋅ mol−1, was derived from vapor pressure measurements determined by a Knudsen mass‐loss effusion technique. Finally, different approaches were used in attempts to calculate the standard enthalpy of formation of TKX‐50 in the solid state. A critical overview and assessment of the data on the enthalpy of formation of TKX‐50 is also presented.

Enthalpy of formation and hydrogen bonded dimerization of furfurylamine: Experimental and computational study

The combustion energy and standard molar enthalpy of formation of liquid furfurylamine were determined using an isoperibol calorimeter with a static bomb. The theoretical calculations were used for the interpretation of experimental calorimetric result. The DLPNO-CCSD(T1)/CBS method in conjunction with isodesmic-type reactions was used to calculate the gas-phase enthalpy of formation of this compound. At the same level of theory, the interconversion of the gauche and anti conformers of furfurylamine and the N–H⋯N hydrogen bonding between them leading to the association into dimeric units were studied. The calculated values of equilibrium and rate constants for reaction gauche → anti and enthalpy of dimerization of two conformers suggest that the gaseous furfurylamine exists predominantly in the dimeric form. An additional support for the strong association of furfurylamine in the vapor phase was obtained from comparison of the enthalpies of formation in liquid and gaseous states: the consistency between these two values was achieved only when a correction for dimerization was applied.

Energetic derivatives of 3,3′,5,5′-tetranitro-4,4′-bipyrazole (TNBPz): Synthesis, characterization and properties

3,3‘,5,5‘-Tetranitro-4,4‘-bipyrazole monohydrate (TNBPz, 1⋅H2O) is an excellent precursor for the synthesis of new energetic materials (2–12). Several nitrogen-rich salts (e.g. guanidinium, aminoguanidinium, hydrazinium, ammonium and hydroxylammonium) were prepared from 1⋅H2O by neutralization reactions. In addition, the N-methylation and N-amination of compound TNBPz was investigated and is reported. All new synthesized energetic materials were fully characterized by NMR (1H, 13C, 14N, and 15N) spectroscopy, infrared spectroscopy, differential thermal analysis (DTA) and elemental analysis. Compounds 2, 4–8 and 10 were characterized with single crystal X-ray diffraction. The heats of formation for compounds 2, 4–6, 8, 11 and 12 were calculated using the atomization method based on CBS-4 M enthalpies. Several detonation parameters, such as detonation pressure, velocity and energy, were calculated by using the X-ray densities and the calculated standard molar enthalpies of formation. The sensitivities of all energetic materials toward external stimuli were tested according to the BAM standards. In addition, the toxicity toward vibrio fischeri bacteria of few energetic salts (3 and 4) is reported.

Thermodynamic Studies on Sr5Nb4O15

The SrO–Nb2O5 system, especially Sr5Nb4O15 compound is of interest for their use as an electroceramics. In this work, Sr5Nb4O15 compound was synthesized by solid-state reaction and characterised by XRD. Thermodynamic properties like heat capacity, enthalpy of formation and Gibbs energy of formation of Sr5Nb4O15 have been measured. The standard molar enthalpy of formation of Sr5Nb4O15(s) was determined using an oxide melt solution high temperature calorimeter. Based on these experimental data, a self-consistent thermodynamic function of this compound was also generated. This thermodynamic data is essential for the optimization of synthesis conditions for materials and for the evaluation of their stability under appropriate technological operating conditions.