Appeared in: 2022, 2023 (3 sets)
Write two differences between order of reaction and molecularity of reaction.
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Official Evaluation Steps & EL10 Insight
Question: Write two differences between order of reaction and molecularity of reaction.
Step 1 (Definition and Theoretical Basis): [1 Mark]
- Order of Reaction: It is the sum of the powers of the concentration terms in the rate law expression. For a reaction $aA + bB \rightarrow \text{Products}$, the rate law is given by $\text{Rate} = k[A]^x[B]^y$, where the order is $n = x + y$.
- Molecularity of Reaction: It is the number of reacting species (atoms, ions, or molecules) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction.
Step 2 (Comparative Analysis and Properties): [1 Mark]
| Feature | Order of Reaction | Molecularity of Reaction |
|---|---|---|
| Nature | It is an experimental quantity determined from the rate law. | It is a theoretical concept determined by the reaction mechanism. |
| Values | It can be zero, fractional, or an integer. | It is always a whole number (never zero or fractional). |
Step 3 (Final Concluded Answer): [Full Marks]
The two fundamental differences are:
- Order of reaction is an experimental value derived from the rate law, whereas molecularity is a theoretical value based on the elementary steps of the reaction mechanism.
- Order can be zero or fractional, while molecularity is always a positive integer (typically 1, 2, or 3).
💡 EL10 Concept Insight: Think of molecularity as the number of people needed to start a dance (you can't have half a person!), while order is like the actual speed of the dance floor, which you can only figure out by watching and timing it, not just by counting the people.