1. The number of molecules that participate in an elementary chemical reaction.
Usage: chemistry; technical

Examples

• The molecularity of a reaction determines how many particles must collide simultaneously for the reaction to occur.
• A unimolecular reaction has a molecularity of one, while a bimolecular reaction has a molecularity of two.
• Chemists use molecularity to understand the mechanism of elementary steps in complex reactions.
• The molecularity of the rate-determining step affects the overall kinetics of the reaction.