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Chemical Kinetics and Nuclear Chemistry question

2025 · 28 Jan · Shift 1 · Q5
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  5. /2025 · 28 Jan · Shift 1 · Q5

Chemical Kinetics and Nuclear Chemistry question

2025 · 28 Jan · Shift 1 · Q5

JEE MainChemistryChemical Kinetics and Nuclear ChemistryMCQ+4 / −1
JEE Main 2025 (Online) 28th January Morning Shift Chemistry - Chemical Kinetics and Nuclear Chemistry Question 14 English For a given reaction R→P,t1/2\mathrm{R} \rightarrow \mathrm{P}, \mathrm{t}_{1 / 2}R→P,t1/2​ is related to [A]0[\mathrm{A}]_0[A]0​ as given in table. Given: log⁡2=0.30\log 2=0.30log2=0.30 Which of the following is true? A. The order of the reaction is 1/21 / 21/2. B. If [A]0[\mathrm{A}]_0[A]0​ is 1 M , then t1/2\mathrm{t}_{1 / 2}t1/2​ is 20010 min200 \sqrt{10} \mathrm{~min}20010​ min C. The order of the reaction changes to 1 if the concentration of reactant changes from 0.100 M to 0.500 M. D. t1/2\mathrm{t}_{1 / 2}t1/2​ is 800 min for [A]0=1.6M[\mathrm{A}]_0=1.6 \mathrm{M}[A]0​=1.6M Choose the correct answer from the options given below:
  1. A
    A and C Only
  2. B
    A, B and D Only
  3. C
    A and B Only
  4. D
    C and D Only
View written solutionFree

Correct answer: B

  1. Use the half-life dependence on initial concentration

    For an nnn-th order reaction (n≠1n\neq 1n=1), t1/2∝1[A]0 n−1=[A]0 1−nt_{1/2} \propto \frac{1}{[A]_0^{\,n-1}} = [A]_0^{\,1-n}t1/2​∝[A]0n−1​1​=[A]01−n​

    So if t1/2∝[A]0mt_{1/2} \propto [A]_0^{m}t1/2​∝[A]0m​ then m=1−n⇒n=1−mm=1-n \quad \Rightarrow \quad n=1-mm=1−n⇒n=1−m

  2. Infer relation from the given table

    From the table, t1/2t_{1/2}t1/2​ increases as [A]0\sqrt{[A]_0}[A]0​​, i.e. t1/2∝[A]01/2t_{1/2} \propto [A]_0^{1/2}t1/2​∝[A]01/2​

    Therefore, 1−n=121-n=\frac121−n=21​ n=12n=\frac12n=21​

    Hence statement A is true.

  3. Find the proportionality constant

    Since t1/2=k′[A]0t_{1/2}=k'\sqrt{[A]_0}t1/2​=k′[A]0​​ using the tabulated data, the constant comes out to be k′=20010 min M−1/2k'=200\sqrt{10}\ \text{min M}^{-1/2}k′=20010​ min M−1/2

    Therefore, for [A]0=1 M[A]_0=1\,\text{M}[A]0​=1M, t1/2=20010×1=20010 mint_{1/2}=200\sqrt{10}\times \sqrt{1}=200\sqrt{10}\ \text{min}t1/2​=20010​×1​=20010​ min

    So statement B is true.

  4. Check statement C

    Reaction order is a property of the rate law under given conditions; it does not change merely because concentration changes from 0.100 M0.100\,\text{M}0.100M to 0.500 M0.500\,\text{M}0.500M.

    So statement C is false.

  5. Check statement D

    For [A]0=1.6 M[A]_0=1.6\,\text{M}[A]0​=1.6M, t1/2=200101.6t_{1/2}=200\sqrt{10}\sqrt{1.6}t1/2​=20010​1.6​

    Now, 10×1.6=16=4\sqrt{10\times 1.6}=\sqrt{16}=410×1.6​=16​=4

    Hence, t1/2=200×4=800 mint_{1/2}=200\times 4=800\ \text{min}t1/2​=200×4=800 min

    So statement D is true.

  6. Select the correct option

    True statements: A, B, D

    Therefore the correct option is: B: A, B and D Only\boxed{\text{B: A, B and D Only}}B: A, B and D Only​

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