Search Results
Abstract
The transformation equation for the thermokinetics of consecutive first-order reactions has been deduced, and a thermokinetic research method of irreversible consecutive first-order reactions, which can be used to determine the rate constants of two steps simultaneously, is proposed. The method was validated and its theoretical basis was verified by the experimental results.
Abstract
A heat conduction microcalorimeter with a sensitivity of 103 V mW-1 and a vessel of 3 cm3 has been designed. The device is equipped with an automatic dosimeter, an original system for injection in titration experiments, and a PC for control, data recording and data analysis. The software allows the determination of (i) overall heat effects, (ii) thermokinetics, and (iii) changes in enthalpy and equilibrium constants in titration experiments.
Abstract
A microcalorimeter (Setaram c-80) was used to study the thermokinetics of the hydration process of calcium phosphate cement (CPC), a biocompatible biomaterial used in bone repair. The hydration enthalpy was determined to be 35.8 J g–1 at 37.0°C when up to 80 mg CPC was dissolved in 2 mL of citric buffer. In the present study, parameters related to time constants of the calorimeter were obtained by fitting the recorded thermal curves with the function θ=Ae–?t(1– e–?2t). The real thermogenetic curves were then retrieved with Tian function and the transformation rate of the hydration process of CPC was found to follow the equation α=1–[1–(0.0075t)3]3. The microstructures of the hydrated CPC were examined by scanning electron microscopy. The nano-scale flake microstructures are due to crystallization of calcium phosphate and they could contribute to the good biocompatibility and high bioactivity.
Abstract
A novel thermokinetic research method for determination of the rate constant of a reaction taking place in a batch conduction calorimeter under isothermal conditions is proposed: the double-thermoanalytical curve method. The method needs only the characteristic time parameter t m, the peak height Δm at time t m and the peak area a*m after time t m for two thermoanalytical curves measured with different initial concentrations of the reactants: it conveniently calculates the rate constants. The thermokinetics of four reaction systems were studied with this method, and its validity was verified by the experimental results.
Abstract
Porphyrins are known as unique ligands forming some of the most stable complexes with various metal ions. In this work the thermokinetic investigations of complex formation of tetraphenylporphyrins with copper(II) acetate were carried out in two anhydrous organic solvents: acetic acid and DMF at 25C. Measurements were performed in a heat conduction microcalorimeter [7] adapted for non-aqueous solvents. Total heat effects and thermokinetics were determined. The results were discussed together with spectrophotometric data. Taking into account the high stability of metalloporphyrin complexes, the heat of their formation is rather small (in the case of acetic acid ΔQ=32.71.2 kJ mol−1, for DMF ΔQ=26.21.3 kJ mol−1). Such result can suggest that: 1) the stability of complexes is influenced strongly by an entropy factor, 2) the complexation involves breaking of the NH-bond in the porphyrin coordination centre, accompanied by high consumption of energy.
Abstract
The thermokinetics of the formation reactions of cerium(III) n-dodecylbenzene sulfonate and cerium(III) stearate are studied by using a microcalorimeter. On the basis of experimental and calculated results, three thermodynamics parameters (the activation enthalpies, the activation entropies, the activation free energies), the rate constant, three kinetic parameters (the activation energies, the pre-exponential constant and the reaction order) and the enthalpies of the reaction of preparing cerium(III) n-dodecylbenzene sulfonate in the temperature range of 20–35C and cerium(III) stearate in the temperature range of44.6–62.8C are obtained. The results showed that the title reactions easily took place in the studied temperature.
Abstract
This paper presents a novel data processing method for thermokinetics of faster first-order reaction on the basis of the double-parameter theoretical model of a conduction calorimeter, in which the rate constant of a first-order reaction can be calculated from only four peak height data from the same thermoanalytical curve without using any peak-area. The saponifications of ethyl acetate and methyl acetate in aqueous solution and ethyl benzoate in aqueous alcohol have been studied to test the validity of this method. The rate constants calculated with this method are in fair agreement with those in literature; hence the validity of this method is demonstrated.
Studies of thermokinetics in an adiabatic calorimeter
II. Calorimetric curve analysis methods for irreversible and reversible reactions
Abstract
The kinetic investigation of thermoanalytical curves for the ethyl acetate and alkaline hydrolysis, requires tedious calculations of several mathematical expressions, to establish the correlation between the thermochemical and kinetic parameters. Using the DSC measured data for the heat flow-temperature dependence of the studied reactions, we have obtained the kinetic bulk parameters and the dependencek=k(T) for the basic and acid hydrolysis of ethyl acetate.
