Kinetics of Nearly Complex Reaction Sequences

The faet that the kineties of an overall reaction normally represent the net effeets of the rates of a number of individual elementary steps means that one of our major eoneems in analysis must be how to assemble the individual steps into the whole. There are systematic procedures for doing this, some of which will be discussed in detail for homogeneous reactions that occur by chain mechanisms. However, we have also pointed out that often, in the absence of detailed information, models that aecount for the essential features of the steps involved in an overall reaetion ean be of great utility. In this seetion we shall diseuss three such schemes that have found useful application in a wide variety of reaetion systems. 

Type I. Parallel reactions with separate reactants and products A B (iti) 

Type II. Parallel reactions with the same reactant  

Type III. Series reactions with a stable intermediate A B C k M) 

In addition to the rate of consumption of reactant or appearance of product, two further quantities are of importance in the analysis of the kinetics of these schemes the yield and the selectivity. These quantities serve to specify the relative importance of the reaction paths that occur and are ordinarily based on some product-to-reactant or product-to-product relationship. Here we shall define yield as the fraction of reactant converted to a particular product, so if more than one product is of interest in a reaction, there can be several yields defined. The yield of product j with respect to reactant i, Yj, is 

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