Concentration and Reaction

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The rate of the following reaction:
Radioactive decay of 90Sr,
is characterized by the rate constant k = 0.024 year-1. What is the half-life (in years) for this reaction at the same conditions when the initial concentrations are 0.0356 M? (Round your answer to 3 significant figures.)
Hint: The units of the rate constant are linked with the order of reaction.

Answer:________________years

  • Concentration and Reaction -

    Radioactive decay is a first order reaction. t1/2 = 0.693/k
    Solve for t1/2.
    It doesn't matter that conditions are changed, the half-life is the same; half life of first order reactions don't depend upon the initial concn. You can show that, however, by using
    ln(No/N) = kt
    Substitute 0.0356 M for No and half that for N and 0.024 for k. t1/2 will be the same as obtained by 0.693/0.024.

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