ACS General Chemistry 2 Practice Exam 2026 – Your Complete Guide to Mastery and Exam Success!

Unlock all questions

This demo includes only 20 questions. Upgrade to access hundreds of questions, flashcards, exam simulations, and disable ads.

Full question bankExam simulationsFlashcards

From $12.50Unlock all

Session length

1 / 20

The half-life for the first-order conversion of cyclobutene to ethylene is 22.7 s at a given temperature. How many seconds are needed for the partial pressure of cyclobutene to decrease from 100 mmHg to 10 mmHg?

0.101 s

52.0 s

75.5 s

First-order decay means the amount of cyclobutene decreases exponentially over time, with a constant half-life. The time to reach a certain fraction of the initial amount relates to how many half-lives have passed. To go from 100 mmHg to 10 mmHg is a reduction by a factor of 10, which corresponds to n = log2(10) ≈ 3.322 half-lives. Each half-life is 22.7 s, so the total time is t = n × t1/2 ≈ 3.322 × 22.7 s ≈ 75.5 s.

Equivalently, using the decay equation and k = ln 2 / t1/2 gives t = (ln([A]0/[A])) / k = t1/2 × (ln 10 / ln 2) ≈ 75.5 s.

5233 s