Question

Consider a certain reaction `A rarr` Products with `k=2.0xx10^(-2)s^(-1)`. Calculate the concentration of `A` remaining after `100s` if the initial concentration of `A` is `1.0 mol L^(-1)`.

Answer 1

For the first order reaction:
`t=2.303/k log([A]_(0))/[A] = (k xx t)/(2.303)`
`k=2.0 xx 10^(-2) s^(-1), t=100s, [A]_(0) = 1.0 mol L^(-1) = 1.0 M`
`log [A_(0)]/[A] = (2.0 xx 10^(-2)s^(-2)) xx (100s)/(2.303) = 0.8684`
`[A_(0)]/[A]`= Antilog 0.8684 = 7.3858, [A] = `[A]_(0)/7.3858 = (1M)/(7.3858) = 0.135 M`