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1
Brooks, S. P. J. "Equilibrium enzymes in metabolic pathways." Biochemistry and Cell Biology 74, no. 3 (May 1, 1996): 411–16. http://dx.doi.org/10.1139/o96-044.
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It is commonly believed that certain reactions in a metabolic sequence may be at or close to equilibrium because of the large excess of catalytic capacity compared to the flux through these enzyme loci. Simple algebraic manipulations can show that the equilibrium and steady state conditions are mutually exclusive. However, solution of the complete reaction schemes for model "equilibrium" reactions shows that they can remain far from equilibrium even though the ratio of enzyme flux to steady state flux through the overall pathway is high. These calculations show that a reaction's proximity to equilibrium depends on the overall flux through the enzyme locus as well as on the kinetic parameters of the other enzymes in the pathway. Thus, combinations of kinetic parameters may exist that allow certain reactions to approach equilibrium but these conditions are not universal.Key words: equilibria, theoretical kinetics, metabolic control.
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Fedotov, Vladislav Kh, Nikolay I. Kol'tsov, and Petr M. Kosianov. "INFLUENCE OF THE AUTOCATALYTIC STAGES ON THE DYNAMICS OF CONJUGATED CHEMICAL REACTIONS." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 63, no. 2 (February 8, 2020): 14–20. http://dx.doi.org/10.6060/ivkkt.20206302.6053.
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Chemical reactions occurring on nonlinear mechanisms, containing the stage of interaction of various reagents (feedback), can exhibit unusual kinetic properties - the multiplicity of equilibria (hysteresis of different shape dependency on the «velocity-parameter»), change the time of the motion to the equilibrium (slow or fast relaxation), sustained oscillations (regular, irregular), etc. All these critical phenomena are usually associated with the appearance of unstable equilibria in the reactions under study. From the kinetic point of view, one of the main causes of instability is the presence of autocatalytic stages in the reaction mechanism. Therefore, it is interesting to study the effect of autocatalytic stages on the kinetics of chemical reactions, especially far from equilibrium. In this regard, the dynamic characteristics of typical conjugate reactions occurring by non-autocatalytic and autocatalytic mechanisms in an isothermal reactor of ideal mixing under the same conditions are compared in this paper. It is shown that the kinetics of these reactions is different: autocatalysis can shift the equilibrium, change the relaxation time and the rate of reactions. In an irreversible consecutive reaction (far from equilibrium) autocatalysis shifts the equilibrium in the direction of increasing the proportion occupied by the surface of the catalyst and the reaction rate dominated by positive autocatalysis. As the reversible processes increase, the balance shifts to the other side, the reaction slows down and autoinhibition begins to prevail. In parallel conjugate reactions, negative autocatalysis is not observed. In both types of the considered conjugate reactions, the maximum positive change in concentrations and velocity due to autocatalysis observed when these reactions are irreversible.
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Tiwari, Bhupendra, S. Kishore, Ninoslav Marina, and Stefano Bellucci. "Fluctuation Theory in Chemical Kinetics." Condensed Matter 3, no. 4 (December 17, 2018): 49. http://dx.doi.org/10.3390/condmat3040049.
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In this research, we study the stability properties of chemical reactions of arbitrary orders. In a given chemical experiment, we focus on the formation of a chemical equilibrium by optimizing the reaction rate. Under infinitesimal simultaneous variations of the concentrations of reacting species, the binary component equilibrium is achieved when either one of the orders or concentrations of reactants vanishes. The chemical concentration capacities of the components are calculated to describe the local stability of the equilibrium. The correlation between the components is obtained as the mixed second-order derivative of the rate with respect to concentrations. The global stability analysis is performed by introducing a symmetric matrix with its diagonal components as the chemical capacities and off-diagonal components as the local correlation. We find that the local chemical stability requires the orders of the reactants to be either negative or larger than unity. The corresponding global stability requires the positivity of a cubic factor over the orders of the reactants. In short, our consideration illustrates how a chemical reaction takes place by attaining its activation state and asymptotically approaches the equilibrium when two components are mixed with arbitrary orders. Qualitative discussions are provided to support our analysis towards the formation of an optimized equilibrium. Finally, along with future directions, we discuss verification of our model towards the formation of carbon-based reactions, formation of organic/inorganic chemical equilibria and catalytic oxidation of C O − H 2 mixtures in presence of Pt.
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Pekař, Miloslav. "Thermodynamics and foundations of mass-action kinetics." Progress in Reaction Kinetics and Mechanism 30, no. 1-2 (June 2005): 3–113. http://dx.doi.org/10.3184/007967405777874868.
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A critical overview is given of phenomenological thermodynamic approaches to reaction rate equations of the type based on the law of mass-action. The review covers treatments based on classical equilibrium and irreversible (linear) thermodynamics, extended irreversible, rational and continuum thermodynamics. Special attention is devoted to affinity, the applications of activities in chemical kinetics and the importance of chemical potential. The review shows that chemical kinetics survives as the touchstone of these various thermody-namic theories. The traditional mass-action law is neither demonstrated nor proved and very often is only introduced post hoc into the framework of a particular thermodynamic theory, except for the case of rational thermodynamics. Most published “thermodynamic'’ kinetic equations are too complicated to find application in practical kinetics and have merely theoretical value. Solely rational thermodynamics can provide, in the specific case of a fluid reacting mixture, tractable rate equations which directly propose a possible reaction mechanism consistent with mass conservation and thermodynamics. It further shows that affinity alone cannot determine the reaction rate and should be supplemented by a quantity provisionally called constitutive affinity. Future research should focus on reaction rates in non-isotropic or non-homogeneous mixtures, the applicability of traditional (equilibrium) expressions relating chemical potential to activity in non-equilibrium states, and on using activities and activity coefficients determined under equilibrium in non-equilibrium states.
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Patra, Sabyasachi, Ashok K. Pandey, Sudip K. Sarkar, and A. Goswami. "Wonderful nanoconfinement effect on redox reaction equilibrium." RSC Adv. 4, no. 63 (2014): 33366–69. http://dx.doi.org/10.1039/c4ra05104a.
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Redox reactions have been found to be favoured with nanoscale confinement of solid matrices. Softening of reaction conditions as well as enhancement of reaction kinetics in confined nanospaces has been demonstrated.
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Rogozhnikov, D. A., and B. V. Kolmachikhin. "Polymetallic Ore Concentration Middlings Nitric Acid Leaching Kinetics." Solid State Phenomena 265 (September 2017): 1065–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.265.1065.
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The purpose of this work is the kinetic evaluation of reactions occurring during nitric acid leaching of pollymetallic sulfide middlings, for the most complete translation of copper, zinc and sulfur in solution and concentration of precious metals in residue. Methodology is pollymetallic sulfide middlings nitric acid leaching kinetics were studied using mathematical methods such as the experimental data numerical differentiation. Relevance/value is the main sulfide minerals kinetic characteristics were obtained for the studied materials, including the rate of the process, order of reaction, the rate constant for the forward and reverse reaction. Findings are the rate of the process is limited by kinetics. The calculated values of kinetic parameters showed that the process kinetics are influenced by such factors as the nature of leachable sulfide, nitric acid concentration, the surface area of the solid sulfide, the system approaches equilibrium at saturation of the liquid phase reaction products.
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Komorsky-Lovrić, Š., and M. Lovrić. "Theory of staircase cyclic voltammetry of two electrode reactions coupled by a chemical reaction." Bulgarian Chemical Communications 51, no. 3 (2019): 348–57. http://dx.doi.org/10.34049/bcc.51.3.4983.
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Two reversible electrode reactions that are connected by either reversible or totally irreversible chemical reactions are theoretically analysed by staircase cyclic voltammetry. The dependence of peak potentials on the thermodynamic and kinetic parameters is calculated. If the mechanism is permanently in equilibrium, the stability constant of the reversible chemical reaction can be determined. Furthermore, the critical kinetic parameter is determined and its application to the measurement of the forward rate constant of the chemical reaction is demonstrated. Also, the influence of the kinetics of electrode reactions is discussed. Keywords: ECE mechanism; Cyclic voltammetry; Theory
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Fedotov, Vladislav Kh, and Nikolay I. Kol'tsov. "KINETICS QUASIINVARIANTS OF CHEMICAL REACTIONS IN CLOSED SYSTEMS." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 62, no. 6 (July 8, 2019): 47–52. http://dx.doi.org/10.6060/ivkkt.20196206.5881.
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The limitations of the dual-method and its extended version of the multi-experiment method in determining the exact time kinetic (thermodynamic) invariants and approximate invariants (quasiinvariants) of chemical reactions in closed isothermal systems are discussed. It is shown that for reactions, which allow except for internal equilibria, also boundary equilibria (multiple equilibria, multiequilibrium), for example, autocatalytic ones, there are always some "inconvenient" boundary values of reagent concentrations. These "uncomfortable" values cannot be used as the initial concentrations (conditions) for non-equilibrium multi-experiments (forward, reverse or intermediate), because for these values of non-equilibrium solutions cease to exist and, consequently, the reaction can proceed only in the equilibrium regime. As a result, the "usual " method of multi-experiments, using only the boundary values of the equilibrium concentrations of reagents, is not applicable. In this paper, a generalization of this method is proposed and a technique for conducting multi-experiments is developed, which is applicable for wider classes of reactions, including those with boundary equilibria, as well as autocatalytic reactions. This generalized method of multi-experiments (MME) allows one to bypass the limitations of the conventional multi-experiment method (dual-method) and to determine the exact time thermodynamic (kinetic) invariants of linear and some nonlinear chemical reactions, as well as approximate time invariants of any nonlinear chemical reactions in closed isothermal systems. The conditions of multi-experiments which are necessary for the correct operation of this method are determined. Examples of using the generalized method of multi-experiments for one-step and two-step nonlinear reactions with one and two independent reagents, respectively, are given. The kinetic time invariants and quasinvariants found with this method are compared with the exact solutions for the cases where they exist.
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Grzesik, Mirosław, and Teresa Witczak. "The influence of the catalyst on the kinetics of ethyl metacrylate synthesis." Polish Journal of Chemical Technology 9, no. 1 (January 1, 2007): 7–9. http://dx.doi.org/10.2478/v10026-007-0003-1.
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The influence of the catalyst on the kinetics of ethyl metacrylate synthesis The synthesis of ethyl metacrylate in the liquid phase was studied. Tungstophosphoric and molybdophosphoric acids, which belong to heteropolyacids group, were used as a catalyst. The chemical compounds from this group are often utilized in the catalysis with regard to their activity and selectivity. The rate equations, reaction rate constants and equilibrium constants have been determined. The reaction order and the kinetic parameters of the kinetic relations were determined by the integral method. All rate equations are formulated with activities taking the non ideal effects of the compounds into consideration. It was found that the kinetics of the esterification of the presented reactions was non-elementary
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Lasaga, Antonio C. "Metamorphic reaction rate laws and development of isograds." Mineralogical Magazine 50, no. 357 (September 1986): 359–73. http://dx.doi.org/10.1180/minmag.1986.050.357.02.
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AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.
11
Gorbachev, Yu E. "Non-equilibrium reaction rates and non-equilibrium effects in chemical kinetics." Journal of Physics: Conference Series 1105 (November 2018): 012121. http://dx.doi.org/10.1088/1742-6596/1105/1/012121.
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Ding, R., A. I. Leonov, and A. Y. Coran. "A Study of the Vulcanization Kinetics of an Accelerated-Sulfur SBR Compound." Rubber Chemistry and Technology 69, no. 1 (March 1, 1996): 81–91. http://dx.doi.org/10.5254/1.3538360.
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Abstract Vulcanization kinetics for a SBR compound was studied by using both curemeter and DSC methods by a kinetic approach. A simplified but realistic model reaction scheme was used to simulate both induction and curing periods simultaneously. Model parameters were extracted from isothermal curemeter experiments. The model prediction demonstrated a good agreement with isothermal curemeter data over a temperature range of 120°C to 180°C. The variation of equilibrium modulus with temperature, observed from cure curves, can also be predicted. However, DSC experiments showed a different reaction behavior in the curing period as compared to model calculations. This was explained by the assumption that the reaction heat observed in DSC is due to all possible exothermal reactions, and the formation of crosslinks is only a part of these reactions. Hence, the curemeter can provide a good indication of crosslink formation, while DSC displays the entire reaction heat released during the vulcanization process. The kinetic approach allows one to incorporate vulcanization kinetics into the practical simulation of reactive processing operations.
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Becker, Erwin W. "Dynamics and Kinetics of Enzymes Kinetic Equilibrium of Forces in Biochemistry." Zeitschrift für Naturforschung C 47, no. 7-8 (August 1, 1992): 628–33. http://dx.doi.org/10.1515/znc-1992-7-823.
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To explain the high specificity, high reaction rate, and high thermodynamic efficiency in enzymatic processes, cooperation of the enzyme with a molecular transfer unit is assumed. A “kinetic equilibrium of forces” is suggested, which enables high reaction rates to occur under equilibrium conditions and a thorough examination of the substrate to be made without consumption of free energy. In case of ATPases, ion-binding proteins are the most probable transfer units. By analyzing the elementary effect in muscle contraction it is shown that the new theorem may be of substantial value in elucidating biochemical processes.
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Mutlu, Ayfer, and Burçin Acar Şeşen. "EVALUATING OF PRE-SERVICE SCIENCE TEACHERS’ UNDERSTANDING OF GENERAL CHEMISTRY CONCEPTS BY USING TWO TIER DIAGNOSTIC TEST." Journal of Baltic Science Education 15, no. 1 (February 20, 2016): 79–96. http://dx.doi.org/10.33225/jbse/16.15.79.
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This research aimed at evaluating pre-service science teachers’ understanding of the subject matters such as “thermochemistry, chemical kinetics, chemical equilibrium, acids and bases and electrochemistry”. For this purpose, a two-tier diagnostic test consisting of 44 items (α = 0.84) related to the aforementioned concepts was developed by the researchers. This test was applied on to the first, second, and third year pre-service science teachers in Hasan Ali Yucel Education Faculty, Istanbul University. The results showed that the pre-service science teachers had alternative conceptions about endothermic-exothermic reactions, conservation of energy, reaction enthalpy, calorimeters; rate of reaction, reaction rate constant, effects of some factors on reaction rate and reaction rate constant; effects of some factors on equilibrium, equilibrium dynamics, Le Chatelier Principle; equivalence point, end point, indicators, buffers, titrations, neutralization, strength and properties of acids and bases, pH; effects of concentrations on cell potential, metal electrodes, localization of anode and cathode, plating, galvanization. Key words: acids and bases, alternative conception, chemical equilibrium, chemical kinetic, electrochemistry, thermochemistry, two tier diagnostic test.
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garfinkle, Moishe. "The thermodynamic natural path in chemical reaction kinetics." Discrete Dynamics in Nature and Society 4, no. 2 (2000): 145–64. http://dx.doi.org/10.1155/s1026022600000145.
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The Natural Path approach to chemical reaction kinetics was developed to bridge the considerable gap between the Mass Action mechanistic approach and the non-mechanistic irreversible thermodynamic approach. The Natural Path approach can correlate empirical kinetic data with a high degree precision, as least equal to that achievable by the Mass-Action rate equations, but without recourse mechanistic considerations. The reaction velocities arising from the particular rate equation chosen by kineticists to best represent the kinetic behavior of a chemical reaction are the natural outcome of the Natural Path approach. Moreover, by virtue of its thermodynamic roots, equilibrium thermodynamic functions can be extracted from reaction kinetic data with considerable accuracy. These results support the intrinsic validity of the Natural Path approach.
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Virkki, Heli, Antti Vuori, and Tapani Vuorinen. "Intramolecular Lactonization of Poly(α-hydroxyacrylic acid): Kinetics and Reaction Mechanism." Journal of Polymers 2015 (September 28, 2015): 1–10. http://dx.doi.org/10.1155/2015/157267.
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Poly(α-hydroxyacrylic acid), PHA, is one of the few polymers with biodegradable properties used in mechanical pulp bleaching to stabilize hydrogen peroxide. A new method for the in situ follow-up of the lactone ring formation of PHA has been developed. The results have further been applied to describe the reaction kinetics of the lactonization and hydrolysis reactions through parameter estimation. In addition, the reaction mechanism is elucidated by multivariate data analysis. Satisfactory identification and semiquantitative separation of the lactone ring as well as the acyclic (carboxyl and hydroxyl groups) forms have been established by 1H NMR in the pH range of 1–9. The lactonization reaction approaching equilibrium can be described by pseudo-first-order kinetics in the pH range of 1–6. The rate constants of the pseudo-first-order kinetic model have been estimated by nonlinear regression. Due to the very low rates of lactonization as well as the weak pH dependency of the reaction, an addition-elimination mechanism is proposed. Additionally, the presence of a transient reaction intermediate during lactonization reaction could be identified by subjecting the measurement data to multivariate data analysis (PCA, principal component analysis). A good correlation was found between the kinetic and the PCA models in terms of model validity.
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Schmitz, Guy, and Henri Rooze. "Cinétique et mécanisme des réactions bromate–chlorite et bromate – dioxyde de chlore." Canadian Journal of Chemistry 66, no. 2 (February 1, 1988): 231–35. http://dx.doi.org/10.1139/v88-038.
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In an acidic solution, containing initially chlorous acid and bromate in excess, two consecutive reactions are observed, the oxidation of chlorous acid to chlorine dioxide followed by the oxidation of chlorine dioxide: BrO3− + 4ClO2 + 2H2O = 4ClO3− + 3H+ + HOBr. The kinetics of this reaction has been studied and a mechanism proposed. It agrees with the one accepted for the related reaction between bromate and Ce(III). Extended by reactions of chlorous acid, the mechanism reproduces the experimental curves of chlorine dioxide evolution in chlorous acid – bromate solutions. The values of the equilibrium and kinetic constantes are discussed.
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Vogel, Kristina, Thorsten Greinert, Monique Reichard, Christoph Held, Hauke Harms, and Thomas Maskow. "Thermodynamics and Kinetics of Glycolytic Reactions. Part I: Kinetic Modeling Based on Irreversible Thermodynamics and Validation by Calorimetry." International Journal of Molecular Sciences 21, no. 21 (November 6, 2020): 8341. http://dx.doi.org/10.3390/ijms21218341.
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In systems biology, material balances, kinetic models, and thermodynamic boundary conditions are increasingly used for metabolic network analysis. It is remarkable that the reversibility of enzyme-catalyzed reactions and the influence of cytosolic conditions are often neglected in kinetic models. In fact, enzyme-catalyzed reactions in numerous metabolic pathways such as in glycolysis are often reversible, i.e., they only proceed until an equilibrium state is reached and not until the substrate is completely consumed. Here, we propose the use of irreversible thermodynamics to describe the kinetic approximation to the equilibrium state in a consistent way with very few adjustable parameters. Using a flux-force approach allowed describing the influence of cytosolic conditions on the kinetics by only one single parameter. The approach was applied to reaction steps 2 and 9 of glycolysis (i.e., the phosphoglucose isomerase reaction from glucose 6-phosphate to fructose 6-phosphate and the enolase-catalyzed reaction from 2-phosphoglycerate to phosphoenolpyruvate and water). The temperature dependence of the kinetic parameter fulfills the Arrhenius relation and the derived activation energies are plausible. All the data obtained in this work were measured efficiently and accurately by means of isothermal titration calorimetry (ITC). The combination of calorimetric monitoring with simple flux-force relations has the potential for adequate consideration of cytosolic conditions in a simple manner.
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Newman, Kenneth E., Raymond E. Ortlieb, Nicole Pawlik, and Jason Reedyk. "Formation of monofluorophosphate from fluoride in phosphoric acid – water and phosphoric acid – sulfuric acid – water mixtures." Canadian Journal of Chemistry 85, no. 5 (May 1, 2007): 346–51. http://dx.doi.org/10.1139/v07-027.
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When dissolved in concentrated phosphoric acid, sodium fluoride reacts rapidly to form monofluorophosphate. In less concentrated acid, the reaction does not proceed to completion, and the reaction kinetics become very much slower. The equilibrium and rate constants for the reaction have been determined. In ternary mixtures of phosphoric acid, sulfuric acid, and water, the formation of monofluorophosphate is considerably enhanced, and the kinetics are rapid. The results are interpreted in terms of the very low water activity coefficients in strong-acid solutions.Key words: monofluorophosphate, monofluorophosphoric acid, 19F NMR, 31P NMR, phosphoric acid, sulufric acid, equilibria, kinetics.
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McClelland, Robert A., N. Esther Seaman, James M. Duff, and R. E. Branston. "Kinetics and equilibrium in the ammonolysis of substituted phthalimides." Canadian Journal of Chemistry 63, no. 1 (January 1, 1985): 121–28. http://dx.doi.org/10.1139/v85-020.
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Kinetic studies are reported for the base hydrolysis to phthalamic acid anions (H) and ammonolysis to phthalamides (A) for seven phthalimides (P): 1, unsubstituted; 2, 4-NO2; 3, 4-Cl; 4, 4-t Bu; 5, 3-NO2; 6, 3-Me; 7, 3-Me3Si. The hydrolysis kinetics require two mechanisms, one which is first order in neutral imide and first order in hydroxide ion, and a second, which is important only in quite concentrated NaOH, which is first order in neutral phthalimide and second order in hydroxide ion. Ammonolysis kinetics for 1–5 revealed the rate law: Rate = kN [Unionized phthalimide] [NH3][OH−]. A mechanism is proposed with rate-determining breakdown of the anionic form of the tetrahedral intermediate derived by addition of NH3 to the phthalimide. The ammonolysis is reversible. The phthalamide hydrolyzes to the phthalamic acid via cyclization to an intermediate phthalimide, which is detected in concentrated base where its formation from phthalamide is more rapid than its subsequent hydrolysis. Rate constants for the cyclization follow the rate law: Rate = kcyc [Phthalamide][OH−]. This reaction is the microscopic reverse of the ammonolysis, and the ratio kN/kcyc provides the equilibrium constant Keq for the reaction P + NH3 = A. Values for 1–5 lie in the range 2 × 102 – 4 × 103. With 3-methylphthalimide, kinetics in aqueous ammonia do not obey a first-order relationship, but they could be analyzed by a scheme whereby the phthalimide is converted reversibly to the phthalamide and simultaneously undergoes an irreversible hydrolysis. The value of Keq in the system is 1.8. With 3-trimethylsilylphthalimide the value of Keq is further reduced to 0.01. The ammonolysis reaction does occur more quickly than hydrolysis but the equilibrium is so unfavorable that even in concentrated ammonia only a small amount of the phthalamide is ever formed.
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Carruthers, Chris, and Heshel Teitelbaum. "Non-equilibrium kinetics of bimolecular reactions. Part 6. Transient rate coefficients." Canadian Journal of Chemistry 72, no. 3 (March 1, 1994): 714–20. http://dx.doi.org/10.1139/v94-096.
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The master equation is solved numerically for the time dependence of the vibrational level populations of HCl (treated as a simple harmonic oscillator) during the bimolecular exchange reaction, Br + HCl → HBr + Cl, taking into account the competition between reaction and vibrational equilibration subject to Landau–Teller T–V excitation. Strong deviations from Boltzmann distributions are found. A wide range of reactant concentrations, diluent concentrations and temperatures were explored. It was found that no significant reaction occurs before the establishment of a steady vibrational population distribution, confirming that the rate coefficient for non-equilibrium bimolecular exchange reactions can be determined from a simple analytical steady state treatment (J. Chem. Soc. Faraday Trans. 87, 229 (1991)). The rate of an isolated elementary bimolecular reaction, A + BC → AB + C, under non-equilibrium conditions can deviate seriously from the standard expression, Keq [A][BC], and is better given by the law[Formula: see text]where [R] is the concentration of the collisional equilibrator, R, and a and g are constants depending only on temperature. This generalized rate law describes not only the initial rate but also the rate all the way up to completion, in the absence of the reverse reaction.
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He, Yuyang, Xiaobin Cao, and Huiming Bao. "Ideas and perspectives: The same carbon behaves like different elements – an insight into position-specific isotope distributions." Biogeosciences 17, no. 19 (October 2, 2020): 4785–95. http://dx.doi.org/10.5194/bg-17-4785-2020.
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Abstract. It is expected that information on the source, reaction pathway, and reaction kinetics of an organic compound can be obtained from its position-specific isotope compositions or intramolecular isotope distribution (Intra-ID). To retrieve the information, we could use its predicted equilibrium Intra-ID as a reference for understanding the observed Intra-IDs. Historically, observed, apparently close-to-equilibrium carbon Intra-ID has prompted an open debate on the nature of biosystems and specifically the pervasiveness of reversible biochemical reactions. Much of the debate remains unresolved, and the discussion has not clearly distinguished between two states of equilibrium: (1) the equilibrium among the corresponding bond-breaking and bond-forming positions in reactant and product and (2) the equilibrium among all carbon positions within a compound. For an organic molecule with multiple carbon positions, equilibrium carbon Intra-ID can be attained only when a specific reaction is in equilibrium and the sources of each position are also in equilibrium with each other. An observed Intra-ID provides limited information on if the sources and pathways are both unconstrained. Here, we elaborate on this insight using examples of the observed Intra-IDs of hydroxyl-bearing minerals, N2O, and acetic acid. Research effort aiming to calibrate position-specific equilibrium and kinetic isotope fractionation factors for defined processes will help to interpret observed Intra-IDs of a compound accurately and fully.
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Vogel, Kristina, Thorsten Greinert, Monique Reichard, Christoph Held, Hauke Harms, and Thomas Maskow. "Thermodynamics and Kinetics of Glycolytic Reactions. Part II: Influence of Cytosolic Conditions on Thermodynamic State Variables and Kinetic Parameters." International Journal of Molecular Sciences 21, no. 21 (October 25, 2020): 7921. http://dx.doi.org/10.3390/ijms21217921.
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For systems biology, it is important to describe the kinetic and thermodynamic properties of enzyme-catalyzed reactions and reaction cascades quantitatively under conditions prevailing in the cytoplasm. While in part I kinetic models based on irreversible thermodynamics were tested, here in part II, the influence of the presumably most important cytosolic factors was investigated using two glycolytic reactions (i.e., the phosphoglucose isomerase reaction (PGI) with a uni-uni-mechanism and the enolase reaction with an uni-bi-mechanism) as examples. Crowding by macromolecules was simulated using polyethylene glycol (PEG) and bovine serum albumin (BSA). The reactions were monitored calorimetrically and the equilibrium concentrations were evaluated using the equation of state ePC-SAFT. The pH and the crowding agents had the greatest influence on the reaction enthalpy change. Two kinetic models based on irreversible thermodynamics (i.e., single parameter flux-force and two-parameter Noor model) were applied to investigate the influence of cytosolic conditions. The flux-force model describes the influence of cytosolic conditions on reaction kinetics best. Concentrations of magnesium ions and crowding agents had the greatest influence, while temperature and pH-value had a medium influence on the kinetic parameters. With this contribution, we show that the interplay of thermodynamic modeling and calorimetric process monitoring allows a fast and reliable quantification of the influence of cytosolic conditions on kinetic and thermodynamic parameters.
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Sieniutycz, Stanisław. "Thermodynamic Structure of Nonlinear Macrokinetics in Reaction-Diffusion Systems." Open Systems & Information Dynamics 11, no. 02 (June 2004): 185–202. http://dx.doi.org/10.1023/b:opsy.0000034196.56929.71.
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Affinity picture — new for transport phenomena — and the traditional Onsagerian picture are shown to constitute two equivalent representations for kinetics of chemical reactions and transfer processes. Two competing directions in elementary chemical or transport steps are analyzed. Nonequilibrium systems are described by equations of nonlinear kinetics of Marcelin-Kohnstamm-de Donder type that contain terms exponential with respect to the Planck potentials and temperature reciprocal. Simultaneously these equations are analytical expressions characterizing the transport of the substance or energy through the energy barrier. We regard kinetics of this sort as potential representations of a generalized law of mass action that includes the effect of transfer phenomena and external fields. We also consider physical consequences of these kinetics closely and far from equilibrium, and show how diverse processes can be described. In these developments we point out the significance of nonlinear symmetries and generalized affinity. Correspondence with the Onsager's theory is shown in the vicinity of thermodynamic equilibrium. Yet, the theory shows that far from equilibrium the rates of transport processes and chemical reactions cannot be determined uniquely in terms of their affinities because these rates depend on all state coordinates of the system.
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Fedotov, Vladislav Kh, and Nikolay I. Kol'tsov. "KINETICS QUASIINVARIANTS OF CHEMICAL REACTIONS IN OPEN SYSTEMS." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 62, no. 8 (August 19, 2019): 76–80. http://dx.doi.org/10.6060/ivkkt.20196208.5891.
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The methods of nonequilibrium multi-experiments are one of the new approaches to solving inverse problems of chemical kinetics and optimization of chemical reactors. Currently, these methods are developed only for closed isothermal systems. In this paper, a generalization of the dual-experiment method and its extended version of the multi-experiment method for open systems is obtained, which allows to determine the approximate kinetic invariants (quasiinvariants) of chemical reactions in open continuous stirred tank reactor. The multi-experiment method for open systems is based on conducting two or more special nonequilibrium (unsteady) experiments under certain conditions. For nonlinear reactions of arbitrary complexity (multi-step, multi-equilibria), simple relations are obtained that allow to calculate the conditions for nonequilibrium experiments necessary for the identification of the reaction mechanism under study. The method allows to use any permissible values, except equilibrium ones, as initial values of reagent concentrations. The technique of carrying out multi-experiments and performing the necessary numerical calculations based on the multiple integration of systems of ordinary differential equations under different initial conditions is developed. The examples of using the developed method for one-stage linear and two-stage nonlinear reactions with two and three reagents are given. Found with the help of this method, the kinetic curves of the nonequilibrium quasiinvariants compared with the nonequilibrium curves of change of concentrations during the whole reaction. It is shown that quasiinvariant curves change within narrower limits than concentrations in different experiments, i.e. remain practically constant in time. The obtained results are also applicable for open nonisothermal systems.
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Amballa, Ram Gopal, Chandra Sekhar Veeravalli, Ravi Kumar Ganta, Raghu Babu Korupolu, and Annapurna Nowduri. "Mn(II) Catalyzed Oxidation of Atenolol by Cerium(IV) in Aqueous Sulfuric Acid Medium: A Spectrophotometer Aided Kinetic, Mechanistic and Thermodynamic Study." Zeitschrift für Physikalische Chemie 232, no. 2 (February 23, 2018): 223–44. http://dx.doi.org/10.1515/zpch-2017-0985.
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AbstractThe kinetics and mechanism of manganese(II) catalyzed oxidation of atenolol by cerium(IV) sulfate in aqueous H2SO4at a constant ionic strength of 0.50 mol dm-3was studied spectrophotometrically. The reaction showed first order kinetics in cerium(IV) whereas fractional order in both manganese(II) and atenolol. Addition of products showed no effect on the rate of the reaction. The main product, 2-(4-(2-hydroxy-3-oxopropoxy)phenyl)acetamide, was identified with the aid of IR and mass spectral data. Stoichiometry with respect to the drug substrate and reagent was established as 2:1. Added H2SO4, SO42−and HSO4−showed negligible effect on the rate of the reaction. HCe(SO4)3−was found to be the predominant reactive species under the specified experimental conditions. The rate constants (k), catalytic constant (kc) and equilibrium constant (K6) for the proposed mechanism were determined. The kinetic and thermodynamic activation parameters were computed for both the slow rate determining step and complex forming equilibrium step.
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Tee, Oswald S., Jana Pika, M. Judith Kornblatt, and Michael Trani. "Rates and equilibrium constants for the covalent hydration of 5-bromo-2(1H)-pyrimidinone in aqueous solution." Canadian Journal of Chemistry 64, no. 6 (June 1, 1986): 1267–72. http://dx.doi.org/10.1139/v86-209.
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The kinetics of bromination of the title compound (1) have been measured in aqueous solutions of pH 0–6. The change in the order of reaction which occurs around pH 2.5 is explained by 1 reacting via its covalent hydrate, 3. Furthermore, there is sufficient 3 present at equilibrium that the kinetics of its equilibration with 1 were also measured. From these two studies the extent of covalent hydration of 1 is estimated to be 5%.Kinetic studies of the bromination of the dimethyl cation 5 and of its equilibration with the pseudobase 6 were also carried out for the purposes of comparison.The present results for 1, 3, 5, and 6 are compared to earlier results for 2-pyrimidinone and analogous derivatives.
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Ning, Hong Long, Lin Feng Lan, Lei Wang, Jun Biao Peng, Zhi Jian Peng, and Ju Sheng Ma. "Interface Reaction Thermodynamics of AgCuTi Brazing Filler Metal and Alumina Ceramic." Advanced Materials Research 936 (June 2014): 1239–46. http://dx.doi.org/10.4028/www.scientific.net/amr.936.1239.
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In this work, the interface reaction between Al2O3 ceramic and Ag70.5Cu27.5Ti2 brazing filler metal at 845-860°C was investigated. Based on the data of thermodynamics and kinetics, the Gibbs free energies of the main interface reactions in the real brazing system condition were calculated. But the values of normal equilibrium reaction condition and the real interface reaction brazing system were different; and the main influential factor was the brazing temperature, and the system vacuum of brazing condition can lead the change of equilibrium constant (Kα). The results revealed that the high temperature and vacuum active brazing is a non-equilibrium interface reaction especially to titanium alloy, the vacuum and alloy liquid solution are beneficial to the brazing process, and the by-product formation of titanium-oxygen are affected by the diffusion process.
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Matte, Denise, Bernard Solastiouk, André Merlin, and Xavier Deglise. "Étude cinétique de la N-chloration de la diméthylamine et de la diéthylamine en phase aqueuse." Canadian Journal of Chemistry 67, no. 5 (May 1, 1989): 786–91. http://dx.doi.org/10.1139/v89-118.
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A complete kinetic study of the N-chlorination, in aqueous medium, of dimethylamine and diethylamine by a stopflow spectrophotometric method is presented. In neutral or basic medium our experimental results can be interpreted by two kinetically indistinguishable mechanisms; the reactions between protonated amine (R2NH2+) and hypochlorite ion (ClO−) and the reaction between R2NH and hypochlorous acid (ClOH) are equivalent because of the fast equilibrium of proton exchange existing between the two groups of possible reactants [Formula: see text]. In acid medium, in the presence of chloride ions, we observed a reaction by aqueous chlorine (Cl2) on the amine (Cl2 + R2NH → chloramine).Keywords: kinetics, N-chlorination, amines, aqueous medium.
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Azis, Thamrin, La Ode Ahmad, Fajrin E. Rosa, and Laode Abdul Kadir. "Study of Equilibrium and Kinetics of Pb(II) in Solution Using Persimmon Tannin Gel as an Adsorbent." Jurnal Kimia Sains dan Aplikasi 22, no. 6 (November 13, 2019): 310–16. http://dx.doi.org/10.14710/jksa.22.6.310-316.
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Heavy metals concentrations exceeding the recommended threshold are hazardous for the environment, so there is a need for handling it safely. The purpose of this research was to determine the adsorption capacity and kinetics of adsorption. This research uses an adsorption method in the process of removing Pb(II) heavy metal ions using persimmon tannin gel. Besides the influence of contact time, pH, and the concentration of Pb(II) metal ions on adsorption, a kinetics study was also carried out. The adsorption rate is obtained through the adsorption rate constant (K) and the reaction order generated from the kinetics model. Based on the results of the research, showed the optimum adsorption process, which is 20 minutes and at a pH of 5. The maximum adsorption capacity of 17.62 mg/g with the value of the standard energy changes of Gibbs adsorption (-ΔG° = -14.274 kJ/moll) indicates that the adsorption takes place through physical interaction. The kinetic adsorption gives the adsorption rates a constant of, k = 0.008231 g/mg.min.
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Chaudhuri, Beauty, and Rupendranath Banerjee. "Kinetics and mechanism of hydroxylamine oxidation by [Fe2III(µ-O)(phen)4(H2O)2]4+ in aqueous media." Canadian Journal of Chemistry 76, no. 3 (March 1, 1998): 350–55. http://dx.doi.org/10.1139/v98-004.
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Equilibrium studies show that in aqueous solutions containing excess 1,10-phenanthroline (phen) in the range pH 3-9, the complex ion [Fe2III ( μ-O)(phen)4(H2O)2]4+ (1) undergoes rapid but partial hydrolysis and coexists with [Fe2III ( μ-)(phen)3(H2O)4]4+ (1d),[Fe2 III ( μ-O)(phen)4(H2O)(OH)]3+ (2), and [Fe2III ( μ-O)(phen)4(OH)2]2+ (3). The solution oxidizes hydroxylamine quantitatively to N2O and is itself reduced to [Fe(phen)3]2+. The reactions in the range pH 3-6 are first-order in concentrations of complex and hydroxylamine but exhibits complex [H+] dependence, suggesting kinetic contributions from 1, 1d, and 2 but not from 3. Rapid formation of inner-sphere adducts between NH2OH and different {Fe2O}4+ species followed by rate-determining one-electron transfer to produce NHOH and {Fe2O}3+ is proposed. All subsequent steps are rapid. Ambient light does not affect kinetics and reaction products.Key words: kinetics, equilibrium, oxo bridge, iron (III), hydroxylamine.
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Mirkes, Evgeny M. "Universal Gorban’s Entropies: Geometric Case Study." Entropy 22, no. 3 (February 25, 2020): 264. http://dx.doi.org/10.3390/e22030264.
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Recently, A.N. Gorban presented a rich family of universal Lyapunov functions for any linear or non-linear reaction network with detailed or complex balance. Two main elements of the construction algorithm are partial equilibria of reactions and convex envelopes of families of functions. These new functions aimed to resolve “the mystery” about the difference between the rich family of Lyapunov functions (f-divergences) for linear kinetics and a limited collection of Lyapunov functions for non-linear networks in thermodynamic conditions. The lack of examples did not allow to evaluate the difference between Gorban’s entropies and the classical Boltzmann–Gibbs–Shannon entropy despite obvious difference in their construction. In this paper, Gorban’s results are briefly reviewed, and these functions are analysed and compared for several mechanisms of chemical reactions. The level sets and dynamics along the kinetic trajectories are analysed. The most pronounced difference between the new and classical thermodynamic Lyapunov functions was found far from the partial equilibria, whereas when some fast elementary reactions became close to equilibrium then this difference decreased and vanished in partial equilibria.
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Rahmawati, Fitria, Wanodya Anggit Mawasthi, and Patiha. "REACTION KINETICS OF Cu ELECTRO-DEPOSITION ON THE SURFACE OF TiO2/GRAPHITE." Jurnal Riset Kimia 8, no. 2 (March 28, 2015): 116. http://dx.doi.org/10.25077/jrk.v8i2.228.
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Research on the kinetics of electrode reaction during copper electro-deposition on the surface of TiO2/graphite has been conducted. The aims of this research are to determine the ratio of anodic reaction rate to cathodic reaction rate , the ratio of anodic rate constant to cathodic rate constant , the equilibrium constant when the reaction reach equilibrium condition and to study the polarization in the electro-deposition reaction. Copper was deposited electrochemically from CuSO4 solution at various concentration i.e. 0.1 M; 0.2 M; 0.3 M; 0.4 M; 0.5 M. In every 5 minutes during electro-deposition process, the pH changes in anode cell was recorded and the change of Cu2+ concentration was also analyzed by spectrophotometric method. The result shows that the reaction order of Cu2+ reduction is first order and the oxidation of H2O in anodic cell is zero order. The ratio of anodic rate constant to cathodic rate constant, is 4.589´10-3 ± 0.071´10‑3. It indicates that the reaction rate in cathode is larger than the reaction rate in anode and it allowed polarization. The electrochemical cell reached equilibrium after 25 minutes with the equilibrium constant is 8.188´10-10 ± 1.628´10-10.
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Dlouhý, Jiří, and Josef Pašek. "Kinetics of hydrogenation amination of 2-propanol with aniline on a copper-chromium catalyst." Collection of Czechoslovak Chemical Communications 54, no. 2 (1989): 326–40. http://dx.doi.org/10.1135/cccc19890326.
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The kinetics of hydrogenation amination of alcohols in the liquid phase were studied in the presence of a copper(II)-chromium(III) catalyst, 2-propanol and aniline were used as the models. In addition to the kinetic investigation of the model reaction as a whole, the partial reaction steps-dehydrogenation of 2-propanol and condensation of aniline with acetone-were also examined. It was proved that, in the reaction of aniline with 2-propanol on the copper-chromium catalyst, the formation of acetone is equilibrium-controlled. The overall rate of amination of 2-propanol with aniline is determined by both the condensation of acetone with aniline and the hydrogenation of the ketimine intermediate. The amination is accelerated by addition of aluminosilicate to the copper-chromium catalyst, which confirms that the ketimine concentration is not equilibrium-controlled.
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Povar, Igor. "The Stoichiometric Uniqueness of Multiple Chemical Reaction Systems in Chemical Thermodynamics, Kinetics and Catalysis – Contributions of Professor Ilie Fishtik." Chemistry Journal of Moldova 15, no. 2 (December 2020): 7–28. http://dx.doi.org/10.19261/cjm.2020.803.
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The main scientific achievements of great significance accomplished by Professor Ilie Fishtik at the University of Iowa and the Worcester Polytechnic Institute, in several fields of the physical chemistry as chemical thermodynamics, kinetics and heterogeneous catalysis were revealed and briefly analysed. Fundamental equations of chemical thermodynamics within the De Donder (stoichiometric) approach were reformulated in terms of a special class of chemical reactions, called as response reactions. Using this approach, the unusual behaviour of chemical equilibrium systems, to interpret the apparent contradictions to Le Chatelier principle and to discover hitherto unnoticed thermodynamic identities, was rationalised. The stabilities of chemical species were formulated in terms of a certain class of stoichiometrically unique chemical reactions and their thermochemical characteristics. A completely new approach for the generation and simplification of kinetic mechanisms for complex reaction systems was developed and applied. Based on a new type of reaction networks, referred to as reaction route graphs, a systematic method of analysis and reduction of a microkinetic mechanism was established and employed.
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Cloonan, Carrie A., Carolyn A. Nichol, and John S. Hutchinson. "Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks." Journal of Chemical Education 88, no. 10 (October 2011): 1400–1403. http://dx.doi.org/10.1021/ed1010773.
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Pekař, Miloslav. "Non-Equilibrium Thermodynamics View on Kinetics of Autocatalytic Reactions—Two Illustrative Examples." Molecules 26, no. 3 (January 22, 2021): 585. http://dx.doi.org/10.3390/molecules26030585.
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Autocatalytic reactions are in certain contrast with the linear algebra of reaction stoichiometry, on which rate equations respecting the permanence of atoms are constructed. These mathematical models of chemical reactions are called conservative. Using a non-equilibrium thermodynamics-based theory of chemical kinetics, it is shown how to introduce autocatalytic step into such (conservative) rate equation properly. Further, rate equations based on chemical potentials or affinities are derived, and conditions for the consistency of rate equations with the entropic inequality (the second law of thermodynamics) are illustrated. The theory illustrated here can be viewed as a tool for verifying and generalizing traditional mass-action kinetics by means of modern non-equilibrium thermodynamics, which is able to deal also with such rather problematic cases.
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Zhu, Chen, Yilun Zhang, J. Donald Rimstidt, and Honglin Yuan. "Measuring reaction rates at equilibrium with the isotope doping method." E3S Web of Conferences 98 (2019): 13003. http://dx.doi.org/10.1051/e3sconf/20199813003.
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Since the time of J. H. van’t Hoff [1], it has been known that chemical equilibrium is dynamic, meaning that at equilibrium, chemical reactions do not cease, but instead the forward and backward reaction rates are equal. The constant concentrations at equilibrium preclude the use of concentrations to measure reaction rates at equilibrium. Therefore, with the exception of a few special cases, no reaction rates at equilibrium have been published in the literature of chemistry, physics, or chemical engineering. Here we report dissolution and precipitation rates at equilibrium for quartz and barite with the isotope-doping method. Experimental data show that dissolution and precipitation rates are equal at equilibrium, indicating the principle of detailed balance (PDB) appear to be applicable at these experimental conditions. The PDB has been a cornerstone for irreversible thermodynamics and chemical kinetics for a long time, and its wide application in geochemistry has mostly been implicit and without experimental testing of its applicability. Nevertheless, many extrapolations based on PDB without experimental validation have far reaching impacts on society’s mega environmental enterprises. The isotope doping method appears to able to test its applicability for a variety of minerals at a wide range of conditions.
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Fedotov, Vladislav Kh, and Nikolaiy I. Koltsov. "METHOD FOR DETERMINING QUASI INVARIANTS IN KINETICS OF CHEMICAL REACTIONS." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 59, no. 5 (July 12, 2018): 72. http://dx.doi.org/10.6060/tcct.20165905.5342.
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A method was developed for determining the approximate kinetic relations (quasi-invariants), which connect equilibrium constants of multi- step reactions with reagent concentrations measured in several non-stationary experiments (multi-experiments). With this method use the quasi-invariants were defined for the oxidation reaction of carbon monoxide proceeding through different mechanisms.
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Alam, M., and Q. Sun. "The kinetics of chemical vapor deposited diamond-oxygen reaction." Journal of Materials Research 8, no. 11 (November 1993): 2870–78. http://dx.doi.org/10.1557/jmr.1993.2870.
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The kinetics of reaction between chemical vapor deposited diamond films (prepared by the hot filament method) and oxygen gas was studied by thermogravimetry. The reactions were carried out at atmospheric pressure in gas mixtures containing between 25 and 100 vol. % oxygen (balance argon), and in the temperature range of 973–1073 K. The apparent order of the reaction is close to 0.6, and the apparent activation energy is 232 kJ/mole. The kinetic data are explained by assuming no mass transfer limitations, direct reaction between CVD diamond and oxygen to form CO and CO2, and thermodynamic equilibrium between CVD diamond, CO, and CO2. The dominant chemical reaction involves the formation of CO, while the formation of CO2 is not significant. Three stage mechanistic schemes are developed involving adsorption of oxygen on CVD diamond surface, surface chemical reaction, and desorption of adsorbed species to CO or CO2. The experimental rate data conform to the reaction rate expressions developed for the mechanistic schemes leading to the formation of CO and CO2, assuming adsorption as the rate-controlling step. The adsorption rate constants for the formation of CO and CO2 are determined. The activation energy of the adsorption step leading to the formation of CO is 213 kJ/mole.
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Gómez-Ríos, David, Howard Ramírez-Malule, Peter Neubauer, Stefan Junne, and Rigoberto Ríos-Estepa. "Degradation Kinetics of Clavulanic Acid in Fermentation Broths at Low Temperatures." Antibiotics 8, no. 1 (January 17, 2019): 6. http://dx.doi.org/10.3390/antibiotics8010006.
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Clavulanic acid (CA) is a β-lactam antibiotic inhibitor of β-lactamase enzymes, which confers resistance to bacteria against several antibiotics. CA is produced in submerged cultures by the filamentous Gram-positive bacterium Streptomyces clavuligerus; yield and downstream process are compromised by a degradation phenomenon, which is not yet completely elucidated. In this contribution, a study of degradation kinetics of CA at low temperatures (−80, −20, 4, and 25 °C) and pH 6.8 in chemically-defined fermentation broths is presented. Samples of CA in the fermentation broths showed a fast decline of concentration during the first 5 h followed by a slower, but stable, reaction rate in the subsequent hours. A reversible-irreversible kinetic model was applied to explain the degradation rate of CA, its dependence on temperature and concentration. Kinetic parameters for the equilibrium and irreversible reactions were calculated and the proposed kinetic model was validated with experimental data of CA degradation ranging 16.3 mg/L to 127.0 mg/L. Degradation of the chromophore CA-imidazole, which is commonly used for quantifications by High Performance Liquid Chromatography, was also studied at 4 °C and 25 °C, showing a rapid rate of degradation according to irreversible first-order kinetics. A hydrolysis reaction mechanism is proposed as the cause of CA-imidazole loss in aqueous solutions.
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Lívanský, Karel. "Kinetics of pH equilibration in solutions of hydrogen carbonate during bubbling with a gas containing carbon dioxide." Collection of Czechoslovak Chemical Communications 50, no. 3 (1985): 553–58. http://dx.doi.org/10.1135/cccc19850553.
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The kinetics of the title process is approximated by differential equations based on kinetic and equilibrium data for carbon dioxide. The course of pH after a sudden change of the concentration of CO2 in the gas is calculated by numerical integration. The course of pH during absorption of CO2 is different from that during desorption. The course of pH during desorption calculated on the assumption that the rate of the noncatalysed hydration of CO2 is sufficient to ensure chemical equilibrium is in good agreement with experimental data from the literature. During absorption of CO2 in a solution of hydrogen carbonate, the chemical reaction rate is sometimes insufficient to ensure chemical equilibrium prior to pH measurement.
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Cummings, R. H., and H. L. Pardue. "Fast kinetic method for methemoglobin developed and adapted for quantification of hemoglobin in whole blood." Clinical Chemistry 33, no. 4 (April 1, 1987): 493–97. http://dx.doi.org/10.1093/clinchem/33.4.493.
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Abstract We studied the kinetics of the reaction of cyanide with methemoglobin (mHb), used the information to develop a fast kinetic method for quantifying methemoglobin, then used that method to quantify hemoglobin (Hb) in whole blood based on the reaction with ferricyanide to produce mHb. Reaction conditions for mHb and cyanide are adjusted to give pseudo-first-order behavior with an apparent rate constant that increases linearly with cyanide concentration, decreases linearly with pH, and follows an Arrhenius-type relationship with temperature. Absorbance change, computed from kinetic data with a curve-fitting method, varies linearly with mHb concentration. Although the reactions are monitored most reliably with stopped-flow mixing, cyanide concentration was used to decrease reaction velocities to be compatible with centrifugal mixing. Kinetic results (y) for Hb in blood by both mixing methods correlate well with equilibrium results (x): y = 1.000x + 0.02 mmol/L, Syx = 0.06 mmol/L with stopped-flow mixing; y = 1.03x + 0.12 mmol/L, Syx = 0.07 mmol/L with centrifugal mixing; r = 0.96 and n = 21 in each case.
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Koukkari, Pertti, Risto Pajarre, and Peter Blomberg. "Reaction rates as virtual constraints in Gibbs energy minimization." Pure and Applied Chemistry 83, no. 5 (April 4, 2011): 1063–74. http://dx.doi.org/10.1351/pac-con-10-09-09.
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The constrained Gibbs energy method has been developed for the use of immaterial entities in the formula conservation matrix of the Gibbs energy minimization problem. The new method enables the association of the conservation matrix with structural, physical, chemical, and energetic properties, and thus the scope of free energy calculations can be extended beyond the conventional studies of global chemical equilibria and phase diagrams. The use of immaterial constraints enables thermochemical calculations in partial equilibrium systems as well as in systems controlled by work factors. In addition, they allow the introduction of mechanistic reaction kinetics to the Gibbsian multiphase analysis. The constrained advancements of reactions are incorporated into the Gibbs energy calculation by using additional virtual phases in the conservation matrix. The virtual components are then utilized to meet the incremental consumption of reactants or the formation of products in the kinetically slow reactions. The respective thermodynamic properties for the intermediate states can be used in reaction rate formulations, e.g., by applying the reaction quotients.
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White, W. B. "Thermodynamic equilibrium, kinetics, activation barriers, and reaction mechanisms for chemical reactions in Karst Terrains." Environmental Geology 30, no. 1-2 (March 24, 1997): 46–58. http://dx.doi.org/10.1007/s002540050131.
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Alonso, Antonio A., Irene Otero-Muras, and Manuel Pájaro. "Routes to Multiple Equilibria for Mass-Action Kinetic Systems." Complexity 2018 (December 12, 2018): 1–13. http://dx.doi.org/10.1155/2018/3912627.
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In this work we explore two potential mechanisms inducing multiple equilibria for weakly reversible networks with mass-action kinetics. The study is performed on a class of polynomial dynamic systems that, under some mild assumptions, are able to accommodate in their state-space form weakly reversible mass-action kinetic networks. The contribution is twofold. We provide an explicit representation of the set of all positive equilibria attained by the system class in terms of a set of (positive parameter dependent) algebraic relations. With this in hand, we prove that deficiency-one networks can only admit multiple equilibria via folding of the equilibrium manifold, whereas a bifurcation leading to multiple branches is only possible in networks with deficiencies larger than one. Interestingly, some kinetic networks within this latter class are capable of sustaining multiple equilibria for any reaction simplex, as we illustrate with one example.
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Fawzy, Ahmed, Saleh A. Ahmed, Ismail I. Althagafi, Moataz H. Morad, and Khalid S. Khairou. "Kinetics and Mechanistic Study of Permanganate Oxidation of Fluorenone Hydrazone in Alkaline Medium." Advances in Physical Chemistry 2016 (July 25, 2016): 1–9. http://dx.doi.org/10.1155/2016/4526578.
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The oxidation kinetics of fluorenone hydrazone (FH) using potassium permanganate in alkaline medium were measured at a constant ionic strength of 0.1 mol dm−3 and at 25°C using UV/VIS spectrophotometer. A first-order kinetics has been monitored in the reaction of FH with respect to [permanganate]. Less-than-unit order dependence of the reaction on [FH] and [OH−] was revealed. No pronounced effect on the reaction rate by increasing ionic strength was recorded. Intervention of free radicals was observed in the reaction. The reaction mechanism describing the kinetic results was illustrated which involves formation of 1 : 1 intermediate complex between fluorenone hydrazones and the active species of permanganate. 9H-Fluorenone as the corresponding ketone was found to be the final oxidation product of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy. The expression rate law for the oxidation reaction was deduced. The reaction constants and mechanism have been evaluated. The activation parameters associated with the rate-limiting step of the reaction, along with the thermodynamic quantities of the equilibrium constants, have been calculated and discussed.
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Crampton, Michael R., and Ian A. Robotham. "Kinetic studies of bold σ -adduct formation and nucleophilic substitution in the reactions of ethyl 2,4,6-trinitrophenyl ether, some phenyl 2,4,6-trinitrophenyl ethers, and phenyl 2,4-dinitronaphthyl ether with aniline in dimethyl sulfoxide." Canadian Journal of Chemistry 76, no. 6 (June 1, 1998): 627–34. http://dx.doi.org/10.1139/v97-225.
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The reaction of ethyl 2,4,6-trinitrophenyl ether with aniline in dimethyl sulfoxide containing Dabco occurs in two stages. The first gives 5, the σ -adduct intermediate on the substitution pathway, which has been identified spectroscopically. The second yields 2,4,6-trinitrodiphenylamine, the substitution product. Kinetic studies show that proton transfer is rate limiting both in the formation of the intermediate and in its subsequent acid-catalysed decomposition. Phenoxide is a considerably better leaving group than ethoxide and the substitution reactions of phenyl 2,4,6-trinitrophenyl ethers and phenyl 2,4-dinitronaphthyl ether with aniline in DMSO occur without the accumulation of intermediates. The kinetics indicate both uncatalysed and base-catalysed pathways. The kinetic and equilibrium data for reaction of the ethyl and phenyl ethers are compared with data for σ -adduct formation from 1,3,5-trinitrobenzene and aniline.Key words: nucleophilic substitution, proton transfer, base catalysis, σ -adducts
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Knížek, Jiří, Erhard Lejdar, and Pavel Vetešník. "Mechanism of acetoacetylation of substituted anilines." Collection of Czechoslovak Chemical Communications 50, no. 2 (1985): 365–74. http://dx.doi.org/10.1135/cccc19850365.
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Kinetics have been studied of the reaction of diketene with substituted anilines, and the reaction rate has been found to depend on relative permittivity of the system. The rate and equilibrium constants have been calculated by combination of rate and equilibrium relations with the relation by Amis; the constants correlate with the Hammett substituent constants. The reaction does not proceed as a simple bimolecular process. A reaction mechanism has been suggested.
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Tang, J. Y. "On the relationships between Michaelis–Menten kinetics, reverse Michaelis–Menten kinetics, Equilibrium Chemistry Approximation kinetics and quadratic kinetics." Geoscientific Model Development Discussions 8, no. 9 (September 3, 2015): 7663–91. http://dx.doi.org/10.5194/gmdd-8-7663-2015.
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Abstract. The Michaelis–Menten kinetics and the reverse Michaelis–Menten kinetics are two popular mathematical formulations used in many land biogeochemical models to describe how microbes and plants would respond to changes in substrate abundance. However, the criteria of when to use which of the two are often ambiguous. Here I show that these two kinetics are special approximations to the Equilibrium Chemistry Approximation kinetics, which is the first order approximation to the quadratic kinetics that solves the equation of enzyme-substrate complex exactly for a single enzyme single substrate biogeochemical reaction with the law of mass action and the assumption of quasi-steady-state for the enzyme-substrate complex and that the product genesis from enzyme-substrate complex is much slower than the equilibration between enzyme-substrate complexes, substrates and enzymes. In particular, I showed that the derivation of the Michaelis–Menten kinetics does not consider the mass balance constraint of the substrate, and the reverse Michaelis–Menten kinetics does not consider the mass balance constraint of the enzyme, whereas both of these constraints are taken into account in the Equilibrium Chemistry Approximation kinetics. By benchmarking against predictions from the quadratic kinetics for a wide range of substrate and enzyme concentrations, the Michaelis–Menten kinetics was found to persistently under-predict the normalized sensitivity ∂ ln v / ∂ ln k2+ of the reaction velocity v with respect to the maximum product genesis rate k2+, persistently over-predict the normalized sensitivity ∂ ln v / ∂ ln k1+ of v with respect to the intrinsic substrate affinity k1+, persistently over-predict the normalized sensitivity ∂ ln v / ∂ ln [ E ]T of v with respect the total enzyme concentration [ E ]T and persistently under-predict the normalized sensitivity ∂ ln v / ∂ ln [ S ]T of v with respect to the total substrate concentration [ S ]T. Meanwhile, the reverse Michaelis–Menten kinetics persistently under-predicts ∂ ln v / ∂ ln k2+ and ∂ ln v / ∂ ln [ E ]T, and persistently over-predicts ∂ ln v / ∂ ln k1+ and ∂ ln v / ∂ ln [ S ]T. In contrast, the Equilibrium Chemistry Approximation kinetics always gives consistent predictions of ∂ ln v / ∂ ln k2+, ∂ ln v / ∂ ln k1+, ∂ ln v / ∂ ln [ E ]T and ∂ ln v / ∂ ln [ S ]T. Since the Equilibrium Chemistry Approximation kinetics includes the advantages from both the Michaelis–Menten kinetics and the reverse Michaelis–Menten kinetics and it is applicable for almost the whole range of substrate and enzyme abundances, soil biogeochemical modelers therefore no longer need to choose when to use the Michaelis–Menten kinetics or the reverse Michaelis–Menten kinetics. I expect removing this choice ambiguity will make it easier to formulate more robust and consistent land biogeochemical models.