After three half-lives of a first-order reaction, what fraction of the reactant remains?
Answer and explanation
Correct answer: D. One eighth (12.5 percent)
- Step 1: Each half-life halves the amount. Step 2. (1/2) cubed = 1/8. Answer: one eighth. Why not the others: One quarter (25 percent) remains after two half-lives, one eighth (12.5 percent) remains after three half-lives, and one sixteenth (6.25 percent) remains after four half-lives.
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