Standard Free Energy Of Formation Research Articles

Probabilistic and maximum entropy modeling of chemical reaction systems: Characteristics and comparisons to mass action kinetic models.

We demonstrate and characterize a first-principles approach to modeling the mass action dynamics of metabolism. Starting from a basic definition of entropy expressed as a multinomial probability density using Boltzmann probabilities with standard chemical potentials, we derive and compare the free energy dissipation and the entropy production rates. We express the relation between entropy production and the chemical master equation for modeling metabolism, which unifies chemical kinetics and chemical thermodynamics. Because prediction uncertainty with respect to parameter variability is frequently a concern with mass action models utilizing rate constants, we compare and contrast the maximum entropy model, which has its own set of rate parameters, to a population of standard mass action models in which the rate constants are randomly chosen. We show that a maximum entropy model is characterized by a high probability of free energy dissipation rate and likewise entropy production rate, relative to other models. We then characterize the variability of the maximum entropy model predictions with respect to uncertainties in parameters (standard free energies of formation) and with respect to ionic strengths typically found in a cell.

The oxidation-resistance mechanism of WTaNbTiAl refractory high entropy alloy

The WTaNbTiAl alloy demonstrated excellent oxidation resistance with a 31.83 mg/cm2 of specific mass gain after 48 h oxidation at 1000 °C in the air environment. Based on the multi-scale microstructural characterizations, a diffusion-controlled three-layers oxide scale model was proposed to explain the oxidation kinetics of this RHEA. In addition, thermodynamic calculation results shed light on the formation mechanism of the oxides based on the standard free energy of formation. The present work uncovered the oxidation-resistance mechanism of WTaNbTiAl RHEA via delicate microstructural analysis of oxides, which assists to guide the design of oxidation-resistant high entropy alloys.

Estimation of the Standard Free Energy of Formation of Bastnasite, REFCO3

The standard Gibbs free energy of formation (ΔGof, 298) of bastnasite, (Ce, La, Nd, Pr)FCO3, was estimated using four different methods. The obtained average values were − 1589.5 kJ/mol for CeFCO3, − 1599.5 kJ/mol for LaFCO3, − 1589.1 kJ/mol for NdFCO3, and − 1595.4 kJ/mol for PrFCO3. The value for cerium bastnasite, CeFCO3, was used to construct a potential vs. pH (Eh-pH) diagram to investigate the stability relations of cerium bastnasite. The diagram shows that CeFCO3 is stable in neutral to basic conditions (pH ~ 6.5–11).

The thermodynamics of uranium salts and their hydrates – Estimating thermodynamic properties for nuclear and other actinoid materials using the Thermodynamic Difference Rule (TDR)

A comprehensive thermodynamic database of experimental standard enthalpy of formation, ΔfHo values, standard free energies of formation, ΔfGo and standard entropies, So298 for uranium salts and their hydrates at 298K and 1bar pressure is assembled. For many of these materials there exist experimental uncertainties or else multiple values (often considerably different) are listed for the same material. The aim of this paper is to showcase the ability of the Thermodynamic Difference Rule (TDR) to provide quite accurate estimates of such data (usually errors are less than 1%) and to provide guidance as to the most trusted value to adopt. In addition, where possible the TDR has been used to estimate missing literature values. New thermochemical data values are predicted and TDR is not reliant on possession of knowledge of crystal structures.

Equilibria and Speciation of Chloramines, Bromamines, and Bromochloramines in Water.

The stabilities and speciation of the halamines in water are difficult to characterize experimentally. We provide theoretical estimates of aqueous standard free energies of formation for inorganic chloramines, bromamines, and bromochloramines, based on high-accuracy theoretical standard free energies of formation in gas phase combined with quantum chemical estimates of Henry's law constant. Based on comparisons between several theoretical and experimental datasets, we assign an error of 1.1-1.2 log unit for equilibrium constants of several reactions leading to halamines in water. The reactions of ammonia with HOCl or HOBr that lead to dichloramine, trichloramine, and tribromamine are found to be thermodynamically more favorable than was previously believed. The newly reported equilibrium data also allow us to propose rate constant values for some hydrolysis and disproportionation reactions of dichloramine, monobromamine, and bromochloramine. Finally, theoretical results indicate aqueous acid dissociation constant (pKa) values of 1.5 ± 1 for NH3Cl+, 0.8 ± 1 for NH3Br+, 11.8 ± 1 for NHCl2, and 12.5 ± 1 for NHBrCl. The present report provides a comprehensive data set describing the free energies of the neutral inorganic halamines, the anionic conjugate base species, and the cationic conjugate acid species, with approximately uniform uncertainty bounds assigned throughout.

Distributions, profiles and formation mechanisms of polychlorinated naphthalenes in cement kilns co-processing municipal waste incinerator fly ash

Co-processing municipal solid waste incinerator (MSWI) fly ash in cement kilns is challenging because the unintentional production of persistent organic pollutants (POPs) during the process is not well understood. The distributions, profiles and formation mechanisms of polychlorinated naphthalenes (PCNs) as new POPs covered under Stockholm Convention in two cement kilns co-processing MSWI fly ash were studied. The average concentrations of PCNs in stack gas samples were 710 ng m−3. The PCN concentration in particle samples collected from different process stages in the cement kilns ranged from 1.1 to 84.7 ng g−1. Three process sites including suspension pre-heater boiler, humidifier tower, and the kiln back-end bag filter were identified to be the major formation sites of PCNs in cement kilns co-processing MSWI fly ash. The PCN distribution patterns were similar to that of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs), which indicates the possibility for simultaneous control of PCNs and PCDD/Fs in cement kilns co-processing fly ash. Chlorination was suggested to be an important formation mechanism of PCNs, and chlorination pathways of PCN congeners are proposed based on the congener profiles. Thermodynamic calculations, including relative thermal energies (ΔE) and standard free energy of formation (ΔG), and the charge densities of the carbon atoms in PCN supported the proposed chlorination mechanisms for PCN formation. The results presented in this study might provide helpful information for developing techniques and strategies to control PCN emissions during cement kilns co-processing MSWI fly ash.

First experimental determination of the solubility constant of coffinite

Dissolution experiments have been performed in order to determine the solubility constant of coffinite, USiO4. Several assemblages of phases were used in under-saturated experiments performed in 0.1molL−1 HCl under Ar atmosphere, as well as in air. These samples were fully-characterized and were composed of either USiO4, solely, or USiO4 and additional oxide byproducts that resulted from the synthesis procedure. The solubility constant of coffinite was determined at 25°C and 1bar (log*KS°(USiO4, cr)=−5.25±0.05), as well as the standard free energy of formation of coffinite (ΔfG°(298K)=−1867.6±3.2kJmol−1), which enables one to infer the relative stability of coffinite and uraninite as a function of groundwater composition. Geochemical simulations using PHREEQC 2 software and the Thermochimie data base indicate that coffinite precipitates at 25°C under reducing conditions, at pH=6, for H4SiO4(aq) concentration of 7 × 10−5molL−1 and U(OH)4(aq) concentration of 10−11molL−1. The ΔfG° value determined was used to calculate the standard free energy associated with the formation of coffinite from a mixture of uraninite and quartz. The value obtained (Δr,oxG°=20.6±5.2kJmol−1) indicates unambiguously that coffinite is less stable than the quartz+uraninite mixture at 25°C. Geochemical simulations using PHREEQC 2 software indicate that coffinite precipitates in solutions supersaturated with respect to UO2(cr), but undersaturated with respect to UO2(am) in aqueous solutions with silica concentrations typical of groundwater. These favorable conditions during the formation of sedimentary uranium ore deposits, as well as slow dissolution kinetics, explain the common occurrence of coffinite.

耐摩耐食用超硬合金の研究開発

Ti-8.4 vol% M-47.4 vol% TiC (M: Cr, Mo, W) alloys were prepared through P/M technology and their microstructures and mechanical properties were investigated. It was noted that TiC grain size of W alloy was much smaller than that of both Cr alloy and Mo alloy. Smaller diffusion coefficient of M in β-Ti phase and smaller absolute value of Helmholtz standard free energy of formation of MC were thought to suppress TiC grain growth. It was found that hardness and transverse-rupture strength of W alloy were much higher than those of both Cr alloy and Mo alloy.

Driving Force in Diffusion and Redistribution of Reducing Agents During Redox Reaction on the Surface of CoFeB Film

Diffusion and redistribution of constituent elements on the CoFeB surface after natural oxidation and annealing were investigated by means of X-ray photoelectron spectroscopy with argon beam sputtering. Boron and iron atoms were found to redistribute into the $\sim 3$ nm-thick oxidized surface by the natural oxidation even at room temperature. After annealing up to 400 °C in vacuum, boron atoms drastically diffused into the oxidized surface to reduce the oxidized iron/cobalt. The migration of boron atoms was observed within the depth of $\sim 6$ nm. In contrast, iron atoms diffused little. The diffusion and redistribution behaviors during the redox reactions, such as the natural oxidation and annealing, are speculated to be related to the values of the standard free energy of formation of oxides. In other words, the reduction nature of elements on the CoFeB surface is speculated to be the driving force in the diffusion and redistribution of iron and boron on the surface during the redox reaction.

Computational Study of the Clustering of a Cyclohexene Autoxidation Product C6H8O7 with Itself and Sulfuric Acid.

We investigate the molecular interactions between sulfuric acid and a recently reported C6H8O7 ketodiperoxy acid formed through autoxidation from cyclohexene and ozone. Structurally similar but larger ELVOC (extremely low volatility organic compound) products formed from autoxidation of monoterpenes are believed to play a major role in the formation and early growth of atmospheric aerosol particles. Utilizing density functional theory geometries, with a DLPNO-CCSD(T)/def2-QZVPP single point energy correction, the stepwise Gibbs free energies of formation have been calculated, and the stabilities of the molecular clusters have been evaluated. C6H8O7 interacts weakly with both itself and sulfuric acid, with standard free energies of formation (ΔG at 298 K and 1 atm) around or above 0 kcal/mol. This is due to the presence of strong intramolecular hydrogen bonds in the peroxyacid groups of C6H8O7. These stabilize the isolated molecule with respect to its clusters, and lead to unfavorable interaction energies. The addition of sulfuric acid to clusters containing C6H8O7 is somewhat more favorable, but the formed clusters are still far more likely to evaporate than to grow further in atmospheric conditions. These findings indicate that the O/C ratio cannot exclusively be used as a proxy for volatility in atmospheric new particle formation involving organic compounds. The specific molecular structure, and especially the number of strong hydrogen binding moieties, are equally important. The interaction between the C6H8O7 compound and aqueous phase sulfate ions indicates that ELVOC-type compounds can contribute to aerosol mass by effectively partitioning into the condensed phase.

Thermodynamic Equilibrium of Xylene Isomerization in the Liquid Phase

This study deals with the thermodynamic equilibrium for xylene isomerization. Experiments performed by several researchers to calculate the equilibrium in the gas phase in the 1990s led to the conclusion that the earlier available thermodynamic data for xylenes, which were mainly based on experimental work performed in the 1940s, were in error. In this work a similar procedure was followed to determine the thermodynamic equilibrium for xylene isomerization in the liquid phase. By means of the thermodynamic functions at saturated conditions presented by the previously mentioned studies, the standard free energies of formation were calculated between 250 K and 550 K. Three different expressions were developed to calculate the equilibrium constants as a function of temperature.

Thermodynamics of TmRhO3, Phase Equilibria, and Chemical Potentials in the System Tm–Rh–O

Phase equilibria in the system Tm–Rh–O at 1200 K is established by isothermal equilibration of selected compositions and phase identification after quenching to room temperature. Six intermetallic phases (Tm3Rh, Tm7Rh3, Tm5Rh3, Tm3Rh2, TmRh, TmRh2±δ) and a ternary oxide TmRhO3 are identified. Based on experimentally determined phase relations, a solid-state electrochemical cell is devised to measure the standard free energy of formation of orthorhombic perovskite TmRhO3 from cubic Tm2O3 and β-Rh2O3 in the temperature range from (900 to 1300) K. The results can be summarized as: ΔGf,ox° ± 104/J·mol–1 = −46474 + 3.925(T/K). Invoking the Neumann-Kopp rule, the standard enthalpy of formation of TmRhO3 from its constituent elements at 298.15 K is estimated as −1193.89 (± 2.86) kJ·mol–1. The standard entropy of TmRhO3 at 298.15 K is evaluated as 103.8 (± 1.6) J·mol–1·K–1. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1200 K and temperature–composition diagrams at c...

Study of the Thermodynamic Properties for Polychlorinated 5,10-Dihydrophenarsazine

136 polychlorinated 5,10-dihydrophenarsazine (PCPhZ) in the ideal gas state at 298.15 K and 101.3 kPa have been calculated at the B3LYP/6-31G* level using Gaussian 03 program, and their thermodynamic parameters were obtained. The isodesmic reactions were designed to calculate standard enthalpy of formation (ΔfHө) and standard free energy of formation (ΔfGө) of PCPhZ congeners. The relations of these thermodynamic parameters with the number and position of Cl atom substitution (NPCS) were discussed, and it was found that there exist high correlation between thermodynamic parameters (heat capacity at constant volume (Cvө), entropy (Sө), ΔfHө and ΔfGө) and NPCS. On the basis of the relative magnitude of their ΔfGө, the order of relative stability of PCPhZ congeners was theoretically proposed.

Improvement on Microstructure and Cracking Susceptibility of Laser-Clad Ni-Based Layers by <i>In Situ</i> Generation of Tantalum Carbides and Borides

Cracking is a serious problem in laser-clad hardfacing layers due to inhomogeneous distribution of coarse brittle phases and stress induced during rapid solidification. Tantalum carbides and borides which can form and precipitate at much higher temperatures are tentatively designed to inhibit the formation of the coarse brittle phases of chromium carbides and borides. It is found by XRD analysis that TaC, Ta4C3, TaB and Ta5B6 were formed in-situ and the coarse brittle phases were largely avoided in laser-clad Ni-based layers. It is also found that the formation sequence of these species is governed by their precipitation temperature instead of the rule determined by the standard free energy of formation. The formation of the chromium carbides and borides is inhibited due to the priority of formation of tantalum carbides and borides during rapid solidification. SEM and penetration visualization examinations show that the microstructure is markedly refined and the cracking susceptibility is significantly reduced by this method. The microhardness of the layers maintains at about 800 Hv.

Theoretical study on hydrophilicity and thermodynamic properties of polyfluorinated dibenzofurans

Logarithm values of octanol–water partition coefficients (log K ow) of polyfluorinated dibenzofurans (PFDFs) were calculated based on group contributions, and their thermodynamic properties in the ideal gas state at 298.15 K and 1.013 × 10 5 Pa were calculated using a combination of quantum mechanical computations performed with the Gaussian 03 program at the B3LYP/6-311G * level. The isodesmic reactions were designed to calculate standard enthalpy of formation ( Δ H f θ ) and standard free energy of formation ( Δ G f θ ) of PFDF congeners. By establishing relationships between these properties (including log K ow, standard state entropy S θ, Δ H f θ , Δ G f θ ) and the number and position of fluorine atom substituents ( N PFS), it was found that the fluorine substitution pattern strongly influences all of these properties of the compounds. The relation curve of log K ow values varying with the fluorine substitution pattern presented a three-level sawtooth shape. Intramolecular repulsive forces exist between an oxygen-adjacent fluorine atom on phenyl ring and the oxygen of dibenzofuran, between ortho-substituted fluorine atoms on a phenyl ring, and between two adjacent fluorine atoms on different phenyl rings. Their repulsion energies were ascertained by comparing Δ G f θ values to be approximately 14 kJ mol −1–17 kJ mol −1, 18 kJ mol −1–22 kJ mol −1 and 7 kJ mol −1–9 kJ mol −1, respectively. According to the relative magnitude of their Δ G f θ , the relative stability order of PFDF congeners was theoretically proposed.

Synthesis and Bio-Spectral Studies of Co(II) Complex of 5-Chloro-2,4-Dihydroxy Butyrophenoneoxime (CDHBOX)

Co(II) complex of 5-chloro-2,4-dihydroxy butyrophenoneoxime (CDHBOX) was synthesized from 5-chloro-2,4-dihydroxy butyrophenoneoxime by using standard protocol, and characterized by elemental analyses, melting point determination and spectral data. The ML2 (metal/ligand) stoichiometry of the complex was determined by spectrophotometric and potentiometric studies, and mass spectral data. The value of stability constant of the complex was found to be 6.94x 108 while its standard free energy of formation is 12.155 kcal/mol at 27ºC. Beer’s law is obeyed in the concentration range 2-15 ppm of Co. The value of molar extinction coefficient and sensitivity as per Sandell’s scale were found to 3.35x 103 L.mol-1cm-1and 0.017 μg Co/cm2 respectively. The value of activation energy and the Arrhenius constant Arrhenius constant were found as 4.949 kjmol-1, 74.39. The IR studies reveal that the phenolic proton is lost on complexation and the oxygen of the phenolic (–OH) and nitrogen of the oximino (=NOH) groups coordinate with Co(II) ion. The electronic spectra and magnetic susceptibility measurement indicate that the complex is paramagnetic and tetrahedral in nature. The antimicrobial activity of different concentrations of ligand and its Co(II)-complex has been evaluated against Curvularia lunata, Fusarium oxysporum and Alternaria alternata fungi and Streproproteus, Staph, Escherchia coli, Klebsella, and pseudomonas bacteria. The results indicated that the ligand (CDHBOX) and its Co(II) complex have good anti-microbial properties.

Reaction between Carbon Dioxide and Mechanically Activated Metal Powder

A fundamental study on the reaction between CO2 and mechanically activated metal powders has been conducted. In this research, the behavior and mechanism of CO2 reaction under various grinding conditions were investigated to fix and reduce CO2. The powder used was placed inside a grinding vessel, and was ground together with the SUJ2 balls in CO2 atmosphere. It was found that only the adsorption of CO2 gas on the ground samples was observed, whereas the decomposition of CO2 was not occurred. The CO2 adsorption increased proportionally with the increase in the grinding speed, weight of sample and number of SUJ2 balls. Furthermore, the CO2 adsorption increased with the decrease in the standard free energy of formation of each metal oxide. The morphology of the sample observed by SEM showed that the samples were not crushed into finer particles, but were only grazed on the sample’s surface. Therefore, it can be said that the CO2 can be adsorbed on the mechanically activated samples by using the centrifugal type ball mill, but in order to enhance the amount of CO2 adsorption, another type of machine with higher grinding intensity should be considered.

Studies of thermodynamic properties and relative stability of a series of polyfluorinated dibenzo- p-dioxins by density functional theory

The thermodynamic properties of 75 polyfluorinated dibenzo- p-dioxins (PFDDs) in the ideal gas state at 298.15 K and 1.013 × 10 5 Pa have been calculated at the B3LYP/6-311G* level using Gaussian 03 program. The isodesmic reactions were designed to calculate standard enthalpy of formation (Δ H f°) and standard free energy of formation (Δ G f°) of PFDDs congeners. The relations of these thermodynamic parameters with the number and position of fluorine atom substitution ( N PFS) were discussed, and it was found that there exist high correlations between thermodynamic parameters (entropy ( S°), Δ H f° and Δ G f°) and N PFS. According to the relative magnitude of their Δ G f°, the relative stability order of PFDD congeners was theoretically proposed.

Determination of the thermodynamic stability of TiB2

The standard free energy of formation of titanium boride (TiB2) was measured by the Electro Motive Force (EMF) method (by using yttria doped thoria (YDT) as the solid electrolyte). Two galvanic cells viz. Cell (I): Pt, TiB2 (s), TiO2 (s), B (s) |YDT| NiO (s), Ni (s), Pt and cell (II): Pt, TiB2 (s), TiO2 (s), B (s) |YDT| FeO (s), Fe (s), Pt were constructed in order to determine the ΔfG° of TiB2. Enthalpy increments on TiB2 were measured by using inverse drop calorimetry over the temperature range 583–1769 K. The heat capacity, entropy and the free energy function have been derived from these experimental data in the temperature range 298–1800 K. The mean value of the standard enthalpy of formation of TiB2 (ΔfH298∘ 〈TiB2〉) was obtained by combining these ΔfG° values and the free energy functions of TiB2 derived from the drop calorimetry data. The mean values of ΔfH298∘ 〈TiB2〉 derived from the ΔfG° data obtained from cell I and II were −322 ± 1.2 kJ mol−1 and −323.3 ± 2.1 kJ mol−1, respectively. These values were found to be in very good agreement with the assessed data.

DFT Study of Structural and Thermodynamic Properties for Polybrominated 5,10-Dihydrophenazines

The structural and thermodynamic properties of 75 polybrominated 5,10-dihydrophenazines (PBDPs) in the ideal gas state at 298.15K and 1.013 × 105 Pa have been calculated at the B3LYP/6-31G* level using the Gaussian 03 program. The isodesmic reactions are developed to calculate the standard enthalpy of formation (ΔfHθ) and standard free energy of formation (ΔfGθ) of PBDP congeners. The relationships of these thermodynamic parameters with the number and position of the Br atom substitution (NPBS) are discussed, and it is found that there exists a high correlation between thermodynamic parameters and NPBS. In addition, the correlations between structural parameters and NPBS are discussed. High correlations were found between the energy of the highest occupied molecular orbital (EHOMO), the most negative atomic partial charge in the molecule (q−) and NPBS, and all R2 values are larger than 0.90.