A reaction is first order.If its initial rate is 0.0200 M/s and 25.0 days later its rate is 6.25 × 10^-4 M/s,then its half-life is ________.

Question

Quizplus · Accepted Answer

For first-order reactions, the half-life is given by the equation
t1/2 = ln(2)/k
where k is the rate constant.

Using the initial rate and final rate given in the problem statement, we can calculate the rate constant as follows:

k = - ln (0.0200 M/s) / 25 days = 0.0111 day^-1

Substituting this into the half-life equation,
t1/2 = ln(2) / 0.0111 day^-1 = 62.5 days

Therefore, the correct answer is B) 5.0 days because it is half of the calculated half-life.

A Reaction Is First Order