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Time for a given percentage of a first-order reaction from its half-life

This type of question, asked 7 times: 26 Jul 2022, 25 Jan 2023, 30 Jan 2023, 31 Jan 2024, 29 Jan 2025, 5 Apr 2026 S1, 6 Apr 2026 S1. All 7 questions below, oldest first.

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  1. Question 1

    26 Jul 2022

    124
    At 30∘C30^{\circ}C, the half- life for the decomposition of AB2AB_{2} is 200 s200\text{ }s and is independent of the initial concentration of AB2AB_{2}. The time required for 80%80\% of the AB2AB_{2} to decompose is (Given: log⁡2=0.30\log2 = 0.30; log⁡3=0.48)\log3 = 0.48)

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  2. Question 2

    25 Jan 2023

    51
    For the first order reaction A→BA \rightarrow B, the half life is 30 min⁡30\text{ }\min. The time taken for 75%75\% completion of the reaction is ____\_\_\_\_ min. (Nearest integer) Given: log⁡2=0.3010\log2 = 0.3010
    log⁡3=0.4771log⁡5=0.6989\begin{matrix} & \log3 = 0.4771 \\ & \log5 = 0.6989 \end{matrix}

  3. Question 3

    30 Jan 2023

    147
    An organic compound undergoes first order decomposition. If the time taken for the 60%60\% decomposition is 40 s40\text{ }s, then the time required for 90%90\% decomposition will be is___ s. (Nearest integer). Given: ln⁡10=2.3;log⁡2=0.3\ln10 = 2.3;\log2 = 0.3

  4. Question 4

    31 Jan 2024

    142
    r=k[A]r = k\lbrack A\rbrack for a reaction, 50%50\% of AA is decomposed in 120 minutes. The time taken for 90%90\% decomposition of AA is ____ minutes.

  5. Question 5

    29 Jan 2025

    117
    Drug X becomes ineffective after 50%50\% decomposition. The original concentration of drug in a bottle was 16mg/mL16mg/mL which becomes 4 mg/mLmg/mL in 12 months. The expiry time of the drug in months is ______\_\_\_\_\_\_ -. Assume that the decomposition of the drug follows first order kinetics.

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  6. Question 6

    5 Apr 2026 S1

    50
    If the half-life of a first order reaction is 6.93 minutes then the time required for completion of 99%99\% of the reaction will be ____\_\_\_\_ minutes. (Given : log⁡2=0.3010\log2 = 0.3010 )

  7. Question 7

    6 Apr 2026 S1

    49
    Sucrose hydrolyses in acidic medium into glucose and fructose by first order rate law with t1/2=3t_{1/2} = 3 hour. The percentage of sucrose remaining after 6 hours is ____\_\_\_\_ . (Nearest integer) (Given : log⁡2=0.3010\log2 = 0.3010 and log⁡3=0.4771\log3 = 0.4771 )