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Worksheet: First-Order Reaction Half-Lives

Q1:

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.

Q2:

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?