A certain first-order reaction A → B is 25% complete in 42 min at 25°C. What is its rate constant? A) 6.8 × 10^-3min^-1 B) 8.3 × 10^-3min^-1 C) 3.3 × 10^-2min^-1 D) -3.3 × 10^-2min^-1 E) 11 min^-1

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Quizplus · Accepted Answer

For a first-order reaction, the rate constant k can be calculated using the formula k = (2.303/t) * log(a/(a-x)), where a is the initial concentration and x is the amount reacted. Here, 25% completion means x = 0.25a, so a/(a-x) = 1/0.75. Substituting t = 42 min, k = (2.303/42) * log(1/0.75) = 6.8 × 10^-3 min^-1.

A Certain First-Order Reaction a → B Is 25% Complete