Question

What is molecularity of a reaction? Is it different from the order of a reaction? Name one bimolecular and one trimolecular gaseous reaction.

Answer 1

The molecularity of an elementary reaction is the number of reactant molecules taking part in the reaction.
Molecularity of a reaction is a theoretical value whereas order of reaction is experimentally determined quantity. Molecularity is always a whole number whereas order can be zero, fractional or negative. Molecularity does not determines the rate of the reaction whereas order determines the rate of the reaction.
Following reaction is bi-molecular gaseous reaction.
$O_3\left(g\right)+O\left(g\right)\to 2O_2\left(g\right)$
Following reaction is tri-molecular gaseous reaction.
$2NO+H_2\to N_2+H_2{O}_2$