alleryStart learning →Which expression gives the half-life of a zero order reaction?
At(1/2) = 0.693/k
Bt(1/2) = [A]0/(2k)
Ct(1/2) = 1/(k[A]0)
Dt(1/2) = 2k[A]0
Answer & Solution
Correct answer: B. t(1/2) = [A]0/(2k)
1. Start from [A] = -kt + [A]0 and set [A] equal to half of [A]0.
2. Then half of [A]0 equals [A]0 minus k times t(1/2).
3. So k times t(1/2) equals half of [A]0, giving t(1/2) = [A]0/(2k).
4. This half-life grows as the starting concentration grows, which is the opposite of second order behaviour.
5. Using 0.693/k here would import the first order result and give a wrong answer.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.4 Integrated Rate Laws_
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