Chapter 4 - MOLECULAR DISSOCIATION AND RADICAL COMBINATION

Abstract

The most difficult part of any chain reaction is the production of the primary free radicals. The most direct way of producing such initial radicals is the decomposition of a normal molecule into two free radicals. The initiation of chain reactions by a thermal decomposition of molecules is quite a difficult process. The first method is the addition of compounds that readily decompose to free atoms or radicals. Examples of such substances are the vapors of sodium, hexaphenyl ethane, iodine, and peroxides. Dissociation of Na 2 into two atoms takes place so readily that the vapor is almost completely dissociated at 100°C. Thus, the addition of sodium vapour to any system is equivalent to the addition of atomic sodium. This chapter presents a number of examples that prove that the overall reaction rate depends on the reactant concentrations and that the overall activation energy varies with the dominant process in chain termination. The chapter also discusses the special aspects of radical generation and recombination in liquids and describes the effects of inhibitors on the rates of chain reactions.