A first order reaction is 20% complete in 10 min. How long it takes to complete 80% ?

Explanation

Applying first order intergral rate equation , rate constant K is given as .
`K = (2.303)/(t) log (a)/(a-x)`
`k = (2.303)/(10) log (100)/(100-20) = 0.0223 min^(-1)`
Time required for 80% completion of the first order reaction , `t_(0.8)`
`t_(0.78) = (2.303)/(K) log (100)/(100-80) = (2.303)/(0.0223) log (100)/(20) = 72.2 `min.