alleryStart learning →As a simple second order reaction proceeds, what happens to its half-life?
AIt shortens as reactant is used up
BIt falls to zero at half reaction
CIt lengthens as reactant is used up
DIt stays constant from start to end
Answer & Solution
Correct answer: C. It lengthens as reactant is used up
1. For a simple second order reaction the half-life is 1 / (k[A]0), inversely proportional to the concentration.
2. As reactant is consumed, the concentration entering that formula keeps falling.
3. A smaller concentration makes the next half-life longer, so successive half-lives stretch out.
4. A constant half-life is the signature of first order kinetics, not second order.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.4 Integrated Rate Laws_
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