Question

The reactant concentration in a zero-order reaction was 6.00×10−2 M after 160 s and 1.50×10−2 M after 305 s . What is the rate constant for this reaction? (I got this answer 3.10*10^-4 M/s) What was the initial reactant concentration for the reaction described in Part A?

The reactant concentration in a first-order reaction was 0.100 M after 40.0 s and 3.80×10⁻³M after 90.0 s . What is the rate constant for this reaction? (I got this answer 6.54*10^-2 1/s) The reactant concentration in a second-order reaction was 0.770 M after 100 s and 4.70*10^-2 M after 780s. What is the rate constant for this reaction?

Answer 1

A) The governing equation of zero order reaction is :-

k*t = [A₀] - [A]

Now, k*160 = [A₀] - (6*10^-2) ........(1)

Also, k*305 = [A₀] - (1.5*10^-2) ......(2)

(2) - (1) we get

k*145 = 0.045

or, k = rate constant = 3.1*10^-4 M/s

using the value of k in (1) we get [A₀] = 0.11 M = initial concentration of the reactant

B) The governing equation for 1st order eaction is :-

k*t = ln{[A₀]/[A]}

Thus, k*40 = ln([A₀]/0.1)......(1)

k*90 = ln([A₀]/0.0038).....(2)

Now, (2) - (1)

k*50 = ln26.32

or, k =0.065 s^-1

C) The governing equation for 2nd order reaction is :-

k*t = (1/[A]) - (1/[A₀])

Thus, k*100 = (1/0.77) - (1/[A₀]) .....(1)

k*780 = (1/0.047) - (1/[A₀]).....(2)

Now, (2) - (1) we get

k*680 = 19.978

or, k = 0.03 M^-1 s^-1