Characteristic experimental features of chain reactions

The reaction is observed to be 3/2 order, so the observed rate constant 

It is in this respect that both the rate and rate constant are composite quantities. 

The build-up is often very fast, e.g. over in 10 4 s, and not observed experimentally under normal steady state conditions. Special fast reaction techniques are required to study the build-up, and analysis of the data requires non-steady state methods. If build-up continues after the steady state concentrations occur, the rate of reaction continues to increase and explosion can occur. 

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