A first-order reaction decomposes 75 g of reactant A in 100 minutes when 100 g is taken initially. How long will it take to decompose 150 g of A when the initial amount taken is 200 g?

100 minutes
200 minutes
150 minutes
175 minutes

Correct answer: 100 minutes

Solution

First-order time depends only on the fraction decomposed; 75/100 = 75% and 150/200 = 75% are the same fraction, so the time is the same, 100 minutes.

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