Chemistry - Chemical Kinetics Question with Solution | TestHub

Initial concentration, $[A{]}_0=0.8$ M

Final concentration, $[A{]}_t=0.2$ M

Time taken, $t=12$ hour

For a first order reaction, the concentration after $n$ half-lives is:

$[A{]}_t=\frac{[A{]}_0}{2^n}$

$0.2=\frac{0.8}{2^n}$

$2^n=4$

$n=2$

The total time is related to the half-life by $t=n\times t_{1/2}$

$12=2\times t_{1/2}$

$t_{1/2}=6$ hour

Answer: 6 hour