Question

What is the molecularity of a chemical reaction $A + 2B \longrightarrow C$, if the rate of formation of C increases by a factor of 2 times on doubling the concentration of A and increases by a factor of 9 on tripling the concentration of B?

• A. 3
• B. 2
• C. 1
• D. Not defined

Answer 1

Answer: (A)

3

Answer 2

The molecularity of a chemical reaction is the number of reacting species involved in an elementary reaction.

In the reaction $A + 2B \longrightarrow C$, if it's an elementary reaction:

• 1 molecule of A
• 2 molecules of B

Therefore, the molecularity is $1 + 2 = 3$.

The rate information confirms this:

• Rate $\propto [A]^1$
• Rate $\propto [B]^2$

This matches the stoichiometry, suggesting it is indeed an elementary reaction.