If the initial concentration of a reactant in a generic zero-order reaction is and it drops to in ex — Chemical Kinetics Chemistry Question
Question
If the initial concentration of a reactant in a generic zero-order reaction is $0.10 \text{ M}$ and it drops to $0.05 \text{ M}$ in exactly $5 \text{ minutes}$, what is the total time required for 100% completion of this reaction from the very start, in minutes?
💡 Solution & Explanation
Rate constant $k = ([A]_0 - [A]_t) / t = (0.10 - 0.05) / 5 = 0.01 \text{ M min}^{-1}$. The time for 100% completion is $t_{100\%} = [A]_0 / k = 0.10 / 0.01 = 10 \text{ minutes}$. Since $0.05 \text{ M}$ is exactly half of $0.10 \text{ M}$, $5 \text{ mins}$ is the half-life. For zero-order, total completion time is $2 \times t_{1/2} = 10 \text{ mins}$.