Classification of Exchange Reactions

Considering the number of atoms participating in the exchange, two kinds of reactions are distinguished three-center exchange reactions 

Reactions of type 1, referred to in the following as simple exchange reactions, involve breaking of one (single, double or triple) chemical bond. In reactions of type 2, called double exchange reactions, two bonds are broken. Reactions with a more complicated structural change such as O + C2H2 CO + CH2 can also be included into type 2. 

The study of the temperature dependence of the rate constant k is the only source of information on elementary thermal reactions. This dependence can be calculated if the reaction cross section and the distribution function of reactants are known (see Section III.8). However, the interpretation of experimental results in terms of these microscopic quantities meets with two difficulties. 

if the reaction occurs under non-equilibrium conditions, the distribution function being often unknown. 

Second, the most important characteristics of the reaction dynamics are, to a considerable extent, lost as a result of averaging, even if the distributions functions are known. For instance, with equilibrium distribution, the temperature depen- 

---