The half-life of a first order reaction is determined to be 92.0 years. How long will it take for the concentration of the reactant to reach 2% of its initial value?

Answer 1

(1/2)^n = .02
n ln .5 = ln .02
n = -3.91/-.693
n = 5.644 half lives
times 92 = 519 years

Answer 2

92.0 years X (multiply) with 5.64386