Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.

Start Practicing

Worksheet: First-Order Reaction Half-Lives


When heated to 4 9 9 C , cyclopropane ( C H 3 6 ) reacts to form its structural isomer propene with a rate constant of 5 . 9 5 × 1 0 4 1 s .

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 1 6 4 of the original value?