### Problem 15.35 (half life)

Posted:

**Wed Mar 13, 2019 7:06 pm**given the half-life, how do we calculate the time needed for a certain amount of the reactant's concentration to decrease using the half-life equation

for example : (problem 15.35)

The half-life for the second-order reaction of a substance A is 50.5 s when [A]

is there a way to calculate these values more quickly using only the half-life equation? or do we have to solve for k using the half-life equation and then solve for time using the integrated rate law

for example : (problem 15.35)

The half-life for the second-order reaction of a substance A is 50.5 s when [A]

_{0}= 0.84 mol/L. Calculate the time needed for the concentration of A to decrease to (a) one-sixteenth; (b) one-fourth; (c) one-fifth of its original value.is there a way to calculate these values more quickly using only the half-life equation? or do we have to solve for k using the half-life equation and then solve for time using the integrated rate law