Molecularity of a Reaction
Defines molecularity as the number of reacting species colliding simultaneously in an elementary reaction and distinguishes it from the order of reaction.
What is Molecularity of a Reaction?
The number of reactant molecules, atoms, or ions that must collide simultaneously for an elementary reaction to occur.
Key points
- Define molecularity of a reaction.
- Differentiate between molecularity and order of reaction.
- Determine the molecularity of elementary reactions.
- Understand the limitations of molecularity.
Common exam trap
Confusing molecularity with the order of reaction.
Definitions
- Term
Molecularity
- Meaning
The number of reactant molecules, atoms, or ions that must collide simultaneously for an elementary reaction to occur.
- Term
Elementary Reaction
- Meaning
A reaction that occurs in a single step, where the molecularity can be directly determined from the stoichiometry of that step.
- Term
Order of Reaction
- Meaning
The sum of the exponents of the concentration terms in the experimentally determined rate law for a reaction.
Learning objectives
Define molecularity of a reaction.
Differentiate between molecularity and order of reaction.
Determine the molecularity of elementary reactions.
Understand the limitations of molecularity.
Prerequisites
Chemical Kinetics
Elementary Reactions
Order of Reaction
Stoichiometry
Common mistakes
Confusing molecularity with the order of reaction.
Assuming molecularity for complex reactions without considering the mechanism.
Assigning fractional or negative molecularity.
Keywords
Molecularity
Elementary Reaction
Order of Reaction
Chemical Kinetics
Collision Theory
Reaction Mechanism
Unimolecular
Bimolecular
Termolecular
Practice preview
For an elementary reaction, the molecularity can be:…
easy
The reaction 2A + B → C is found to be elementary. What is the rate law for this reaction?…
medium
Consider the reaction mechanism: Step 1: A + B → C (slow) Step 2: C + D → E (fast). What is the molecularity of the rate-determining step?…
hard