alleryStart learning →For which reaction order is the half-life independent of the starting concentration?
AZero order reactions only
BSecond order reactions only
CFirst order reactions only
DEvery order behaves this way
Answer & Solution
Correct answer: C. First order reactions only
1. For first order the half-life is 0.693/k, and no concentration appears in it.
2. So each successive half-life takes the same length of time, as seen when a peroxide solution halves every 6.00 hours.
3. For zero order the half-life is [A]0/(2k), which does contain the starting concentration.
4. For second order it is 1/(k[A]0), which also contains it.
5. So only first order reactions have a half-life free of concentration.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.4 Integrated Rate Laws_
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