Relating to Reaction Mechanisms and Elementary Reactions

Even a simple reaction usually takes place in a complex manner involving multiple steps making up a reaction mechanism. For example, the formation of ammonia, represented by the simple reaction N2 + 3H2 2NH3, does not take place in the manner 

The original reaction mechanism (Rice and Herzfeld, 1934) proposed for the formation of C2H4 from C2H6 consists of the following five steps  

We use this example to illustrate and define several terms relating to reaction fundamentals  

Elementary reaction a chemical reaction step that takes place in a single molecular encounter (each of the five steps above is an elementary reaction) it involves one, two, or (rarely) three molecular entities (atoms, molecules, ions, radicals, etc.). Only a small number of chemical bonds is rearranged. 

Reaction mechanism a postulated sequence of elementary reactions that is consistent with the observed stoichiometry and rate law these are necessary but not sufficient conditions for the correctness of a mechanism, and are illustrated in Chapter 7. 

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