JEE Main · 2019 · Shift-IImediumCK-080

For the reaction, 2A + B products, when the concentration of A and B both were doubled, the rate of the reaction…

Chemical Kinetics · Class 12 · JEE Main Previous Year Question

Question

For the reaction, 2A+B→\mathrm{2A + B \rightarrow} products, when the concentration of A and B both were doubled, the rate of the reaction increased from 0.3 mol L−1 s−10.3\,\mathrm{mol\,L^{-1}\,s^{-1}} to 2.4 mol L−1 s−12.4\,\mathrm{mol\,L^{-1}\,s^{-1}}. When the concentration of A alone is doubled, the rate increased from 0.3 mol L−1 s−10.3\,\mathrm{mol\,L^{-1}\,s^{-1}} to 0.6 mol L−1 s−10.6\,\mathrm{mol\,L^{-1}\,s^{-1}}.

Which one of the following statements is correct?

Options
  1. a

    Order of the reaction with respect to B is 2

    ✓
  2. b

    Total order of the reaction is 4

  3. c

    Order of the reaction with respect to A is 2

  4. d

    Order of the reaction with respect to B is 1

Correct Answera

Order of the reaction with respect to B is 2

Detailed Solution

Order w.r.t. A: When [A] doubles (B constant): rate doubles (0.3→0.6). So order w.r.t. A = 1.

Order w.r.t. B: When both doubled: rate increases 8× (0.3→2.4). 8=2a×2b=21×2b⇒2b=4⇒b=28 = 2^a \times 2^b = 2^1 \times 2^b \Rightarrow 2^b = 4 \Rightarrow b = 2

So order w.r.t. B = 2, total order = 1 + 2 = 3.

Checking options:

  • (1) Order w.r.t. B is 2 ✓
  • (2) Total order is 4 ✗ (it's 3)
  • (3) Order w.r.t. A is 2 ✗ (it's 1)
  • (4) Order w.r.t. B is 1 ✗

Answer: Option (1)

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