For reaction A → B with rate constant 10⁻³ s⁻¹ (first order), concentration after 1000 s if [A]₀ = 1 M:
Ae⁻¹ ≈ 0.37 M
B0.5 M
C1 M
D0.1 M
Answer & Solution
Correct answer: A. e⁻¹ ≈ 0.37 M
[A] = [A]₀ e^(-kt) = 1 × e^(-10⁻³ × 1000) = e⁻¹ ≈ 0.37 M. (After one 'mean lifetime' τ = 1/k, only 1/e remains.)
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