A first order reaction is 20% complete in 5 minutes. Calculate the time taken for the reaction to be 60% complete

Explanation

For first order reaction `k=(2.303)/(t)log (a)/(a-x)`
To calculate the first order rate constant
Rate constant k=`(2.303)/(5 min)log(100)/(80) =(2.303)/(5 min)log 1.25`
`=0.04464 min^(-1)`
Time taken for 60% completion `t=(2.303)/(k)log(100)/(40) =(2.303)/(0.446 min^(-1))log (100)/(40)`
`t=(2.303)/(0.0446 min^(-1))log2.5 =20.53 min`