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Rate constant of a first order reaction from the fraction reacted or left after a given time

This type of question, asked 16 times: May 2021 S1, 3 May 2023 S2, 10 May 2023 S1, 15 May 2023 S1, 16 May 2023 S2, 9 May 2024 S2, 11 May 2024 S2, 12 May 2024 S2, 14 May 2024 S2, 19 Apr 2025 S1, 13 Apr 2026 S1, 16 Apr 2026 S2, 17 Apr 2026 S2, 18 Apr 2026 S1, 19 Apr 2026 S1, 14 May 2026 S1. All 16 questions below, oldest first.

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  1. Question 1

    May 2021 S1

    65
    What is the rate constant of a first order reaction, if 0.08 mole of reactant reduces to 0.02 mole in 23.03 minutes?

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  2. Question 2

    3 May 2023 S2

    64
    What is rate constant of a first order reaction if 60% reactant decompose in 45 minute?

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  3. Question 3

    10 May 2023 S1

    76
    Calculate rate constant of first order reaction if concentration of reactant decreases by 90% in 30 minute?

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  4. Question 4

    15 May 2023 S1

    92
    A first order reaction takes 40 minute for 20% decomposition. Calculate its rate constant.

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  5. Question 5

    16 May 2023 S2

    64
    In a first order reaction 60% of the reactant converts into product in 45 minutes. Calculate rate constant of the reaction.

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  6. Question 6

    9 May 2024 S2

    66
    Calculate the rate constant of first order reaction if the concentration of the reactant decreases by 90% in 30 minutes.

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  7. Question 7

    11 May 2024 S2

    94
    Calculate the rate constant of the first order reaction if 80% of the reactant reacted in 15 minutes.

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  8. Question 8

    12 May 2024 S2

    83
    A first order reaction takes 23.0323.03 minutes for 20%20\% decomposition. Calculate its rate constant.

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  9. Question 9

    14 May 2024 S2

    80
    Calculate the rate constant of the first order reaction if 80% of the reactant decomposes in 60 minutes.

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  10. Question 10

    19 Apr 2025 S1

    62
    In a first order reaction concentration of reactant decreases from 20 milli mol dm  −3\ ^{- 3} to 8 milli mol dm  −3\ ^{- 3} in 40 minutes, find rate constant of reaction?

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  11. Question 11

    13 Apr 2026 S1

    27
    In first order reaction, 20 % concentration remains after 10 min. What would be the rate constant of reaction if log⁡10(5)=0.6989\log_{10}(5) = 0.6989?

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  12. Question 12

    16 Apr 2026 S2

    29
    If for a first-order reaction, [A]0=1.0[A]_0 = 1.0 M and [A]t=0.25[A]_t = 0.25 M after 276 s, find the value of the rate constant (k).

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  13. Question 13

    17 Apr 2026 S2

    29
    In first order reaction 20 millimole of reactant is reduced to 10 millimole in 1.1511.151 minute. Find rate constant.

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  14. Question 14

    18 Apr 2026 S1

    27
    In a first order reaction 20 millimole of reactant is lowered to 10 millimole in 0.30100.3010 minute. Find rate constant of the reaction?

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  15. Question 15

    19 Apr 2026 S1

    28
    A first order reaction take 3030 minutes for 75%75\% decomposition, calculate its rate constant ?

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  16. Question 16

    14 May 2026 S1

    25
    A first-order reaction takes 2020 minutes to reach 15%15\% completion. Calculate the rate constant of the reaction.

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