Worksheet: First-Order Reaction Half-Lives

In this worksheet, we will practice interpreting and converting between the half-lives and rate constants of first-order reactions.


When heated to 499C, cyclopropane (CH36) reacts to form its structural isomer propene with a rate constant of 5.95×10s.

Calculate the half-life of this first-order reaction.

Calculate the percentage of cyclopropane remaining after 0.750 h, to two significant figures.

Calculate the ratio of cyclopropane to propene after 0.434 h, to two significant figures.


The half-life of a drug in the body of a patient is 42 days. If the drug degrades by a first-order process, how much time is needed for the drug concentration to decrease to 164 of the original value?

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