alleryA reaction is second order with respect to a reactant. If the concentration of that reactant is reduced to half, how does the rate change?
ABecomes one-half
BBecomes one-fourth
CRemains unchanged
DBecomes double
Answer & Solution
Correct answer: B. Becomes one-fourth
1. Rate $= k[A]^2$.
2. New rate $= k\left(\tfrac{[A]}{2}\right)^2 = \tfrac{1}{4}k[A]^2$.
3. So the rate becomes one-fourth of the original.
4. Distractor A applies a first order dependence by mistake.
_Source: syllabus Chemistry Ch 3 "Chemical Kinetics", p.24_
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