Editing Chain reaction (section)

===Typical steps===
The main types of steps in chain reaction are of the following types.<ref name=Laidler288/>
* [[Chain initiation|Initiation]] (formation of [[Active center (polymer science)|active particles]] or chain carriers, often [[free radical]]s, in either a thermal or a photochemical step)
* [[Chain propagation|Propagation]] (may comprise several elementary steps in a cycle, where the active particle through reaction forms another active particle which continues the reaction chain by entering the next elementary step). In effect the active particle serves as a catalyst for the overall reaction of the propagation cycle. Particular cases are:
** chain branching (a propagation step where one active particle enters the step and two or more are formed);
** [[chain transfer]] (a propagation step in which the active particle is a growing [[polymer]] chain which reacts to form an inactive polymer whose growth is terminated and an active small particle (such as a radical), which may then react to form a new polymer chain).
* [[Chain termination|Termination]] (elementary step in which the active particle loses its activity; e. g. by [[Recombination (chemistry)|recombination]] of two free radicals).

The ''chain length'' is defined as the average number of times the propagation cycle is repeated, and equals the overall reaction rate divided by the initiation rate.<ref name=Laidler288/>

Some chain reactions have complex [[rate equation]]s with [[Order of reaction#Fractional order|fractional order]] or [[Order of reaction#Mixed order|mixed order]] kinetics.