Question: In a first-order reaction, if the concentration of reactant decreases from 0.8 M to 0.2 M in 20 minutes, what is the rate constant? (2022)

Options:

1. 0.0347 min⁻¹
2. 0.0693 min⁻¹
3. 0.1 min⁻¹
4. 0.2 min⁻¹

Correct Answer: 0.0347 min⁻¹

Solution:

Using the first-order rate equation, k = (ln[A₀] - ln[A]) / t. Here, k = (ln(0.8) - ln(0.2)) / 20 = 0.0347 min⁻¹.