Question

A) The rate constant for a certain reaction is k = 2.60×10−3 s−1 . If the initial reactant concentration was 0.200 M, what will the concentration be after 16.0 minutes

B)A zero-order reaction has a constant rate of 4.20×10⁻⁴M/s. If after 60.0 seconds the concentration has dropped to 9.00×10⁻²M, what was the initial concentration

Answer 1

we have:

[A]o = 0.200 M

t = 16.0 min = 16*60 s = 960 s

k = 0.0026 s-1

By seeing the unit of k, we can say it is 1st order reaction

use integrated rate law for 1st order reaction

ln[A] = ln[A]o - k*t

ln[A] = ln(0.2) - 2.6*10^-3*960

ln[A] = -1.609438 - 2.6*10^-3*960

ln[A] = -4.105438

[A] = 1.648*10^-2 M

Answer: 1.648*10^-2 M

B)

we have:

[A] = 9.00*10^-2 M

t = 60.0 s

k = 4.20*10^-4 M/s

use integrated rate law for 0 order reaction

[A] = [A]o - k*t

9.00*10^-2 M = [A]o - 4.20*10^-4*60

[A]o = 0.115 M

Answer: 0.115 M