Dental Admissions Test (DAT) Practice Test

What is true about the half-life of the reactant in a first-order reaction?

1. a. It decreases with time

2. b. It increases with time

3. c. It is constant

4. d. It is independent of the initial concentration of the reactant

The correct answer is: d. It is independent of the initial concentration of the reactant

In a first-order reaction, the half-life of the reactant is constant. This means that regardless of the initial concentration of the reactant or the time that has passed since the reaction started, the time it takes for half of the original concentration of the reactant to be consumed remains the same. This is a characteristic feature of first-order reactions and is independent of other factors, hence making option D the correct answer. The other options are incorrect because: A. In a first-order reaction, the half-life does not decrease with time. B. In a first-order reaction, the half-life does not increase with time. C. The half-life of the reactant in a first-order reaction is not constant; it remains the same.