[Olympiad] A reaction A → B follows second-order kinetics. If the rate constant is 0.05 M⁻¹s⁻¹, how long (in seconds) will it take for the concentration of A to decrease from 0.8 M to 0.2 M?
- 5 s
- 10 s
- 75 s
- 20 s
📝 Detailed explanation
For second-order: 1/[A] - 1/[A]₀ = kt.1/0.2 - 1/0.8 = 0.05 * t
5 - 1.25 = 0.05 * t
3.75 = 0.05 * t
t = 3.75 / 0.05 = 75 s.