AP Chemistrymediummcq1 pt
A first-order decomposition has a half-life of 12 minutes. What percentage of the original reactant concentration remains after 36 minutes?
A.12.5%
B.25%
C.50%
D.6.25%
Explanation
Core Concept
Thirty-six minutes equals three consecutive half-lives, since 36 divided by 12 is 3. Each half-life cuts the remaining amount in half, so the fraction left is (1/2)^3 = 1/8. As a percentage, 1/8 of the original concentration is 12.5 percent. Constant half-lives make this counting strategy valid for every first-order process.
Correct Answer
A12.5%
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