Question

If it takes 87.0 min for the concentration of a reactant to drop to 20.0% of its initial value in a first-order reaction, what is the rate constant for the reaction in the units min-1?

Answer 1

0.0185 min⁻¹

Step-by-step explanation:

Using integrated rate law for first order kinetics as:

`[A_t]=[A_0]e^(-kt)`

Where,

`[A_t]` is the concentration at time t

`[A_0]` is the initial concentration

Given:

20.0 % of the initial values is left which means that 0.20 of
`[A_0]` is left. So,

`\frac {[A_t]}{[A_0]}` = 0.20

t = 87.0 min

`\frac {[A_t]}{[A_0]}=e^(-k* t)`

`0.20=e^(-k* 87.0)`

k = 0.0185 min⁻¹