Thermal Gas-Phase Generation of Active Centers

As already stated (p. 188), a chemical chain reaction occurs via free atoms and radicals. Consequently, the formation of such active centers is a condition for the generation of chains. 

One of the possibilities of chain generation is the thermal production of active centers usually involving dissociation of molecules to atoms or radicals. 

The high quasistationary concentrations of some active species, greatly exceeding their final equilibrium concentrations, represent a specific feature of such reactions. 

For example, compare the independent reactions Hg 2H, Cb 2 Cl, with the reaction 

For simple dissociation reactions the mass action law reads 

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