Question

A first order reaction 'has a specific reaction rate of 10⁻² s⁻¹. How much time will it take for 10 g of its reactant to be reduced to 2.5 g?

Answer 1

Given:

First-order reaction

Rate constant: k = 10⁻² s⁻¹

Initial amount: [A]₀ = 10 g

Final amount: [A] = 2.5 g

By using first-order integrated rate law

`k = 2.303/t log ([A]_0/([A]))`

⇒ `t = 2.303/k log ([A]_0/([A]))`

= `2.303/10^-2 log (10/2.5)`

= 230.3 × log (4)

= 230.3 × 0.6021

t = 138.6 seconds