Actually 2 H2 + O2 ----> 2 H2O has about 14 reaction steps.
"Another important consideration is the formation of chain reactions. The basic premise of chain reaction mechanisms is also that free radicals play a leading role in the destruction of reactant molecules. The chain reaction mechanism itself consists of several steps: initiation, propagation, branching (not always present), and termination. This can be illustrated, for certain range of temperature and pressure, by some of the reactions in the following Hydrogen oxidation mechanism:"
"To summarize, reaction mechanisms can be assembled from elementary reactions using free radicals as the means for decomposition of the reactant, and intermediate products. Chain branching reactions, if they occur, take a very important role in the mechanism as they lead to the formation of increasing concentrations of radicals. Reaction time and temperature have a bearing on radical concentration, and the type of reaction initiating the consumption of the reactant"
