Question

After 43.0 minutes, 34.0% of compound decomposed. What is the half-life of this reaction assuming first order kinetics?

Answer 1

34% decomposition means that 66% of the compound remained, meaning the ratio of current to initial concentration after 43 minutes was 0.66. The decomposition equation:

ln[A] = ln[Ao] - kt
ln( [A] / [Ao] ) = -kt

Now, we substitute the given values:
ln(0.66) = -k(43)
k = 9.66 x 10⁻³

half life = ln(2) / k
half life = 71.8 minutes.