Kinetic Significance of Steps in Complex Chemical Transformation

Kinetic Significance of Steps in Complex Chemical Transformation 

This chapter is aimed to show the importance of determining the kinetic significance of individual chemical steps to illuminate the essence of the reaction mechanism. A short overview is presented and a critical analysis is given for the existing methods that assess the significance of chemical species and individual steps in the kinetic models of chemical reaction systems. 

Kinetic study of a complex chemical reaction ultimately comes to the construction of a mathematical model for it. In this case, to solve each specific task on modeling a chemical reaction, as a rule a researcher selects the following strategy (see, for example [1-10])  

Definition of the problem, which mainly comes to answer the question what is the purpose of the kinetic model (describing experimental data, understanding the chemical nature of the reaction, revealing the nature of new chemical phenomena, obtaining the prognostic model for successfully controlling and so on). 

Construction of a hypothesis concerning the kinetic model of the reaction. Mostly it means a definition of a sequence of steps, as the species for the kinetic model of the reaction. Here the possibility of using the computer approaches to construct the primary hypothesis about the reaction mechanism also should be taken into consideration. This question will be discussed in Chapter 3. 

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It follows from such comprehension of the main point of complex chain reaction that it is an imavoidable situation when it becomes clear, what chemical transformations can occim in the interaction between the species of the reaction system (and with what probability) and whether it is difficult to forecast their impact on the complex chemical transformation as a whole. For illustration let us refer to the well-studied example of the chain reaction between molecular hydrogen and oxygen (see Chapter 1). In this case one can clearly conceive a chemism of the reaction having available its kinetic model. However, identification of the kinetic significance of steps in the behavior of a chain reaction requires performing a special system analysis. 

Recent efforts of the authors resulted in development of a munerical method for the analysis of reaction mechanisms, based on their Hamiltonian systematization with marking out target characteristics of reactions and with the kinetic comprehension of conjugate variables. The core factor of this approach is the ability to calculate numerically the dynamics of value magnitudes, which characterize the systenuc kinetic significances of the chemical species of a reaction and its individual steps. Such information makes it possible to realize chemically the mechanism of a complex transformation, and particularly, to carry out the purposeful selection of efficient ways to control the reactions. 

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