8. In 30 minutes, a first-order reaction is 50% complete. Calculate the amount of time it took to complete 87.5 percent of the reaction. a) 30 minutes b) 60 minutes c) 90 minutes d) 120 minutes
Answer: c Explanation: In 30 minutes, the reaction is 50% complete. As a result, t1/2 = 30 minutes. In two half-lives, 75% of the process is accomplished. As a result, t = 2 30 = 60 minutes. In three half-lives, 87.5 percent of the reaction is finished. Hence, t = 3 × 30 = 90 minutes.
