Relationship between molecularity and the reaction order
Molecularity applies to single elementary reaction steps and is seldom higher than 2.
The reaction order is the &quot;effective molecularity&quot; of the whole set of linked reactions, if it had been a single step reaction. It need not to be integer and has just indirect relation to molecularities of elementary steps.
The reaction order is either determined experimentally, either derived from the reaction schema via determined conditions for steady states of intermediate products.