Chemistry / Unit 9 Chem 1706 short lesson, about 20 seconds
Molecularity: Unimolecular and Bimolecular Steps
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The idea
An elementary step's molecularity is its number of particles: a unimolecular step involves one, a bimolecular step involves two.
In practice
Cyclobutane's decomposition to ethylene is a single unimolecular step; in ozone's mechanism, O3 reacting with O to form two O2 is bimolecular.
Where people slip
Molecularity counts particles in one elementary step — it describes an overall reaction only for a single-step reaction.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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