Identify the correct statement :
Show Hint
- Molecularity of a reaction is an experimental quantity.
- For complex reactions molecularity has no meaning.
- Molecularity of a reaction can be zero or even a fraction.
- Molecularity more than three is very common in chemical reactions.
The Correct Option is B
Solution and Explanation
• Molecularity: The number of reacting species (atoms, ions, or molecules) that must collide simultaneously to bring about a chemical reaction in an elementary step.
• Complex Reaction: A reaction that proceeds through a sequence of elementary steps (a mechanism).
Step 1: Distinguishing between theoretical and experimental quantities.
Molecularity is a theoretical concept derived from the reaction mechanism/elementary step. It is not something measured in a lab. In contrast, the Order of Reaction is an experimental quantity. Therefore, statement (A) is incorrect.
Step 2: Analyzing Molecularity in the context of complex reactions.
For a complex reaction, the overall reaction doesn't occur in a single collision. Each individual step in the mechanism has its own molecularity. However, the term "molecularity" as applied to the overall balanced equation of a complex reaction is physically meaningless. We only discuss the "order" of a complex reaction (usually determined by the slowest step). Thus, statement (B) is the correct choice.
Step 3: Evaluating possible values for Molecularity.
Molecularity represents a count of colliding particles. You cannot have zero molecules colliding to form a product, nor can you have half a molecule participating in a collision. Therefore, molecularity is always a positive integer (1, 2, or 3). Statement (C) is incorrect.
Step 4: Considering high molecularity reactions.
The probability of four or more molecules colliding at the exact same moment with the correct orientation is statistically negligible. Consequently, molecularity greater than three is extremely rare. Statement (D) is incorrect. Final Answer: The correct statement is (B).
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Reason (R): Two molecules of the reactants are involved in simultaneous collision between them. - Assertion (A) : The molecularity of the given reaction is 2.
\( 2\text{HI} \longrightarrow \text{H}_2 + \text{I}_2 \)
Reason (R) : Two molecules of the reactants are involved in simultaneous collision between them.
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