A first-order reaction has a specific rate constant of exactly . How much absolute time will it take — Chemical Kinetics Chemistry Question

💡 Solution & Explanation

Reducing the mass from 20 g to 5 g represents exactly two half-lives ($20 \rightarrow 10 \rightarrow 5$). For a first-order reaction, $t_{1/2} = 0.693 / k = 0.693 / 10^{-2} = 69.3 \text{ s}$. The total time is $2 \times 69.3 = 138.6 \text{ s}$.