Which of the following statements is NOT true for a second-order reaction?

Its rate constant can have a value of 1 * 10^(-2) L mol^(-1) s^(-1)
Its half-life is inversely proportional to its initial concentration
The time to complete 75% of the reaction is twice its half-life
t_(50%) = 1 / (k * [A]₀)

Correct answer: The time to complete 75% of the reaction is twice its half-life

Solution

For a second-order reaction: integrated law gives 1/[A] - 1/[A]₀ = kt. t_(50%) = 1/(k[A]₀) (half-life, inversely proportional to [A]₀). t_(75%) = time when [A] = [A]₀/4: 4/[A]₀ - 1/[A]₀ = kt => 3/[A]₀ = kt => t_(75%) = 3/(k[A]₀) = 3 * t_(1/2), not 2 * t_(1/2). Statement C (t₇₅% = 2 * t_(1/2)) is NOT true.

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