Proportional equations, method kinetic analysis

The kinetic and thermodynamic characterisation of chemical reactions is a crucial task in the context of thermal process safety as well as process development, and involves considering objectives as diverse as profit and environmental impact. As most chemical and physical processes are accompanied by heat effects, calorimetry represents a unique technique to gather information about both aspects, thermodynamics and kinetics. As the heat-flow rate during a chemical reaction is proportional to the rate of conversion (expressed in mol s 1), calorimetry represents a differential kinetic analysis method [ 1 ]. For a simple reaction, this can be expressed in terms of the mathematical relationship in Equation 8.1 ... 

The above-mentioned approaches take for granted that the spectra of all the reactants are known. This is not at all the case in kinetic analysis, although usually at least the intermediates are unknown. As is demonstrated in Chapter 5, even reactions can be evaluated under these circumstances. But usually the constants obtained from the over-determined system of differential equations are only proportional to the interesting kinetic constants or a combination of them. For this reason absorption spectroscopy is likely to be combined with other methods. An example of combination with fluorescence and with chromatographic principles is given in Chapter 5. 

Equation 18.12 is the basis for the derivative approach to rate-based analysis, which involves directly measuring the reaction rate at a specific time or times and relating this to [A]fl. Equation 18.11 is the basis for the two different integral approaches to kinetic analysis. In one case, the amount of A reacted during a fixed time is measured and is directly proportional to [A]o ( fixed-time method) in the other case, the time required for a fixed amount of A to react is measured and is also proportional to [A]o variable-time method). Details of these methods will be discussed in Section... 

When more than one reactant is present in the rate equation, the isolation method can be used together with the differential method. The isolation method requires the use of one reactant in large excess while the concentration of the isolated reactant is varied in this case, kinetic analysis is conducted in stages using one isolated reactant at a time. However, this method of partial analysis has to be employed with caution in solid-catalyzed reactions since, in certain reactions, a large excess of any one reactant may have an adverse effect on the active sites of the catalyst. Linearized equations of the form presented in Example 2 can easily be handled by the computational methods available even if reactant concentrations are comparable but present in non-stoichiometric proportions ... 

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