Question

A compound decomposes by a first order reaction. We are told that the initial concentration is 0.0350M. After 65 seconds, the concentration of the compound is 0.0250M. What is the concentration of the compound after 1.47 minutes?

Answer 1

Answer – Given, first order, [A]o = 0.0350 M, t = 65 s , [A]t =0.0250 M ,

At time , t = 1.47 min , [A]t = ?

First we need to calculate the rate constant from the given

We know

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

ln 0.0250 M / 0.0350 = -k * 65 s

-0.336 = -k *65 s

So, k = 0.336/65

         = 0.00518 s^-1

Now at time, t = 1.47 min = 88.2 s

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

ln [A]t / 0.0350 = -0.00518 s^-1 * 88.2 s

                         = 0.456

Taking antiln form both side

A]t / 0.0350 = 0.633

So, [A]t = 0.633*0.0350

              = 0.0222 M