Question

Chapter 13, Question 29 The conversion of C5H1Br into CsHo follows first-order kinetics, with a rate constant of 0.385 h. If the initial concentration of CSHBr is 0.125 M, find (a) the time at which the concentration will be 1.52 x 10 M (b) the concentration after 3.0 h of reaction. Click if you would like to Show Work for this question: Open Show Work

Answer 1

a)
we have:
[A]o = 0.125 M
[A] = 1.52*10^-3 M
k = 0.385 h-1

use integrated rate law for 1st order reaction
ln[A] = ln[A]o - k*t
ln(1.52*10^-3) = ln(0.125) - 0.385*t
-6.489 = -2.079 - 0.385*t
0.385*t = 4.41
t = 11.45 h
Answer: 11.5 h

b)
we have:
[A]o = 0.125 M
t = 3.0 h
k = 0.385 h-1

use integrated rate law for 1st order reaction
ln[A] = ln[A]o - k*t
ln[A] = ln(0.125) - 0.385*3
ln[A] = -2.079 - 0.385*3
ln[A] = -3.234
[A] = e^(-3.234)
[A] = 3.938*10^-2 M
Answer: 3.94*10^-2 M