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6 February, 14:53

For a particular first-order reaction, it takes 3.0 minutes for the concentration of the reactant to decrease to 25% of its initial value. what is the value for rate constant (in s-1) for the reaction?

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  1. 6 February, 18:21
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    We will use this formula for first order:

    ㏑[A] = - Kt + Ao

    when we have t (given) = 30 min = 30 x 60 = 1800 s (we here convert time from min to second.

    then we assume that the initial concentration Ao = 1

    and the concentration of A (final concentration = 0.25

    So by substitution:

    ㏑ (0.25) = - K * 1800 + ㏑ (1)

    1.39 = K * 1800

    ∴ K = 0.00077 s^-1 or 7.7 x 10^-4
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