alleryA reaction has k = 0.05 s⁻¹. After how many seconds is 90% complete?
A20 s
B46 s (≈ ln 10 / k)
C100 s
D30 s
Answer & Solution
Correct answer: B. 46 s (≈ ln 10 / k)
For 1st order, t = (1/k) ln([A]₀/[A]) = (1/0.05) ln(1/0.1) = 20 × 2.303 ≈ 46 s.
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