Reaction kinetics at linearly increased temperature. I. Comparative characterization of reactions in solution and solid phase in a unique “mechanistic diagram”

The temperature dependence of the rate of chemical reactions has been known for a long time; very often it is characterized by the Arrhenius plot. However, kinetic methods that take this phenomenon into account in one measurement in a planned manner have been applied to reactions in solution only in isolated examples-with the exception of the temperature jump method developed by Eigen et al. for fast reactions, based on a stepped temperature program. A mathematical analysis, however, reveals to the chemist that from the point of view of information theory the course of the reaction rate versus time under conditions of constantly increasing temperature is the measured signal which should lead to the most effective understanding of the reaction mechanism. Analysis of the measured peaks, which may overlap, allows the characterization of reactions either in the solid state or in solution by "mechanistic coordinates", which extend the concept of reaction order. Their behavior allows further experiments to be planned, enabling elementary steps to be eliminated. Each reacting system can be characterized kinetically by one series of experiments using different starting concentrations for each reactant and, additionally, using different heating rates. The experimental verification of these considerations can be seen in ca. 1400 DTA and UV experiments for ca. 120 different systems. Furthermore, the example of the oscillating Belousov-Zhabotinsky reaction shows that "fast" reactions frequently may also be recognized. A test for proposed reaction mechanisms is provided by integration programs which allow immediate comparison between experimental and theoretical signal curves.

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New strategies for studies on the kinetics and energetics of the Belousov‐Zhabotinskii reaction

Koch

Nagy-Ungvárai

1987

Ber Bunsenges Phys Chem

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Catalysis / Chemical Kinetics / Computer Experiments / Oscillatory Chemical Reactions / Thermal AnalysisThe oscillatory Belousov-Zhabotinskii reaction and its subsystems were studied by z 1700 DTA and UV experiments performed at linearly increased temperature. The starting concentrations of bromate, bromide, catalyst, and malonic acid were varied in order to obtain "concentration codes" of such series. These represent the dependence of any parameters in discrete ranges of the starting concentrations of the different components. Particularly adequate for a model check are the mechanistic codes (= MCC's), which concern the shape index and reaction type index: If these mechanistic coordinates remain constant in such a concentration interval, other data, e.g. activation energies, can be attributed to a rate-determining process. -The results led to a nine-step model which is based on the FKN mechanism and is capable of roughly reproducing the influence of the initial concentrations and heating rate on 11 parameters characteristic of the envelope and of the oscillations of the experimental signals. The MCC's of the experimental and theoretical series are similar, revealing 4-5 rate-determining steps in the different concentration ranges. -The activation energies agree with values from the literature, cited for three steps; these and further resulting activation energies are consistent with our studies with subsystems.

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Reaction kinetics at linearly increased temperature. I. Comparative characterization of reactions in solution and solid phase in a unique “mechanistic diagram”

Cited by 22 publications

References 46 publications

Zeitlineare Temperaturführung — der Weg zu einer neuen Reaktionskinetik

Zeitlineare Temperaturführung — der Weg zu einer neuen Reaktionskinetik

Linear Control of Temperature with Time—A New Approach to Reaction Kinetics

New strategies for studies on the kinetics and energetics of the Belousov‐Zhabotinskii reaction

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