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A method is described for determination of the kinetic parameters of reversible reactions under isothermal and non-isothermal conditions in thermal analysis. Reversible reactions of the first and second orders and of mixed types are considered. The kinetic parameters of the forward and reverse reactions are determined on the basis of the initial integral data of the thermoanalytical experiment. The results of processing a computerized experiment demonstrated that the suggested method is satisfactorily applicable.

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The relationship between the degree of moving away from equilibrium, the kinetic parameters and the experimental conditions is provided by solving a mass balance equation for the gaseous products of reversible decompositions. The ways to reduce the share of the reverse reaction in the total rate of reaction are discussed. The conditions of non-equilibrium CaCO3 decomposition are defined.

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Studies of thermokinetics in an adiabatic calorimeter

II. Calorimetric curve analysis methods for irreversible and reversible reactions

Journal of Thermal Analysis and Calorimetry
Authors: S. Zhan, J. Liu, Z. Qin, and Y. Deng
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Abstract  

Radiotracer experiments are presented on 241Am uptake in natural aqueous suspensions from a reservoir and a river in SW Spain. The uptake was followed by measuring the 241Am activity in water using a liquid scintillation technique. Experimental results revealed a three-step kinetics in the uptake, which could be satisfactorily described by a model of two parallel and reversible reactions followed by a consecutive weakly-reversible reaction. This paper also studies the effects of the concentration of suspended matter and the specific surface area on the kinetic transfer coefficients.

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Abstract  

The suitability of zone electrophoresis and of free-liquid electrophoresis for investigation of the physico-chemical forms of trace elements in aqueous solutions has been examined. Comparison of the electrophoretic mobilities of tervalent cerium determined by these two methods has demonstrated that adsorption of trace elements on the supporting medium renders zone electrophoresis unsuitable for investigation of hydrolytic and other reversible reactions of trace elements accompanied or preceded by significant adsorption. Free-liquid electrophoresis should be preferably used for this purpose as it is much less complicated by adsorption effects.

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Abstract

The author proposed a method for analyzing kinetics of non-stoichiometry by observing cyclic mass change behavior under cyclic temperature change. Because relationship between the mass and the mass change rate is independent on the previous thermal history of the specimen, we can get equivalent isothermal curves (synthesized isothermal curves) by extracting datum pairs of mass and mass change rate at a given temperature and many conversions, changing the frequencies. The equivalent isothermal curves are really the same as curves of conversion and rate of conversion observed isothermally, so that conventional methods for kinetic analysis can be similarly applied to the equivalent isothermal curves. When multiple elementary processes are proceeding, they can be separately observed by changing the frequency, so that, the method proposed in this short communication is useful and effective to elucidate kinetics of non-stoichiometry as well as reversible reactions.

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Abstract  

The kinetics of complexation (C) and decomplexation (D) reactions between Eu(III) and Aldrich humic acid (HA) was investigated as a function of pH (pH 4, 5, 6, 7 and 8) in the system Eu(III) - HA - Amberlite IR-120(Na) (I = 0.1). The derivation of the kinetic differential equations was based on the reactions of Eu3+ with, so called, strong (HAS) and weak (HAW) carboxylic groups of HA formulated in accordance with the new complexation model.1 The differential equations determining d[EuaHAS]/dt and d[EubHAW]/dt have the classical form applicable for reversible reactions where the forward reaction is the C-reaction and the reverse one is the D-reaction. Kinetic model used for the evaluation of experimental data includes these differential equations and the film diffusion model of sorption of Eu3+ on Amberlite IR-120(Na).

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Abstract  

The reaction thermodynamic and kinetic equations for the non-reversible reactions are established. The enthalpy change of formation reaction of manganese(II) histidine (His) complex in water has been determined by microcalorimetry, using manganese chloride with L-a-histidine at 298.15-323.15 K. The standard enthalpy of formation of Mn(His)2 2+(aq) has been calculated. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constants, along with three kinetic parameters (the apparent activation energies, the pre-exponential constant and the reaction order) are obtained. The results show that the reaction easily takes place over the studied temperature range. The solid complex Mn(His)2Cl24H2O was prepared and characterized by IR and TG-DTG.

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Abstract  

Electrospray ionization mass spectrometry (ESI-MS) was used for the study of cyclization of organic chelating compounds (chelators). Four chelating compounds were studed: Symmetrical ethylenediaminediacetic acid (s-EDDA), Unsymmetrical ethylenediaminediacetic acid (u-EDDA), N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), and N-(2-hydroxyethyl)iminodiacetic acid (HEIDA). The chelators were cyclized with treatments of acids and heating. The open and cyclized form of the chelators were semi-quantified by both positive and negative ion modes ESI-MS. The kinetics of chelator cyclization was studied as a function of reaction temperature and the pH of the matrix. The cyclization of s-EDDA was found to be a pseudo-first order reaction in s-EDDA and overall second order. The cyclizations of HEIDA and HEDTA are reversible reactions. Higher temperature and lower pH favors cyclization.

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A study has been carried out of the influence of sample dilution, the nature of the gas atmosphere, and the static or flowing conditions of this, on the DTA curves resulting from the thermal decomposition of solids. The results obtained seem to indicate that only the reversible reactions of solid thermal decomposition are seriously affected by such factors.

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