Class JEE Chemistry ALL Q #1243
COMPETENCY BASED
APPLY
4 Marks 2026 JEE Main 2026 (Online) 22 January Morning Shift MCQ SINGLE
Consider a first order reaction: $A\to \text{products}$ . 3 different solutions are taken rate of reaction : Solution 1: $100mL~10M~'A' - r_{1}$ ; Solution 2: $200mL~10M~'A' - r_{2}$ ; Solution 3: $100mL~10M~'A' + 100ml~\text{water} - r_{3}$ . The correct order of the rates of reactions is :
(A) $r_{1}=r_{2}=r_{3}$
(B) $r_{1}=r_{2} \lt r_{3}$
(C) $r_{1}=r_{2}\gt r_{3}$
(D) $r_{1} \lt r_{2}=r_{3}$

AI Tutor Explanation

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Step-by-Step Solution

For a first-order reaction, the rate law is given by: \( r = k[A] \), where \( k \) is the rate constant and \( [A] \) is the concentration of reactant A.

Solution 1:

Volume = 100 mL, Concentration = 10 M

\( r_1 = k \times 10 \)

Solution 2:

Volume = 200 mL, Concentration = 10 M

\( r_2 = k \times 10 \)

Solution 3:

Initial volume of A = 100 mL, Initial concentration = 10 M

Final volume = 100 mL (A) + 100 mL (water) = 200 mL

Using the dilution formula, \( M_1V_1 = M_2V_2 \):

\( 10 \times 100 = M_2 \times 200 \)

\( M_2 = \frac{10 \times 100}{200} = 5 \text{ M} \)

\( r_3 = k \times 5 \)

Comparing the rates:

\( r_1 = 10k \), \( r_2 = 10k \), \( r_3 = 5k \)

Therefore, \( r_1 = r_2 > r_3 \)

Correct Answer: \( r_{1}=r_{2}\gt r_{3} \)

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AI Suggestion: Option C

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the rate law for a first-order reaction to compare the rates in different scenarios.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding the concept of rate laws and how concentration affects the rate of a first-order reaction.
Syllabus Audit: In the context of JEE, this is classified as COMPETENCY. The question assesses the student's ability to apply the concepts of chemical kinetics to solve a problem, rather than just recalling definitions or formulas.