order vs molecularity

Question

Which statement is correct?

RankGuru · Accepted Answer

1. **Order of Reaction**: This is purely an **experimental** property. It is the sum of the powers of the concentration terms in the experimentally determined rate law.
2. **Molecularity**: This is a **theoretical** property. It refers to the number of reacting species (atoms, ions, or molecules) that collide simultaneously to bring about proof of an elementary step.
3. **Key Comparison**:
   - **Order**: Can be zero, fractional, or an integer. Determined from experimental data.
   - **Molecularity**: Always a positive integer ($1, 2, 3$). It has no meaning for complex (multi-step) reactions.

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order vs molecularity

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