10. The decomposition of cyclopropane has a rate constant of 6.7 x 10-4 s-1. If the initial concentration of cyclopropane is 1.50 M, what is the concentration of cyclopropane after 650 s?

Answer 1

As indicated by units of k, this is a first order reaction.

You can use the integrated rate law [A] = [A]_oe^-kt or you can use half life.

First order half life = 0.693/k = 0.693/6.7x10^-4 s^-1 = 1034s = t_1/2

number of half lives elapsed = 650 sec x 1 half life/1034 sec = 0.63 half lives elapsed

Fraction remaining = 0.5ⁿ where n is # half lives elapsed

Fraction remaining = 0.5^0.63

Fraction remaining = 0.65

Concentration remaining = 1.5 M x 0.65 = 0.975 M