A zero order reaction is 20% complete in 20 minutes. Calculate the value of the rate constant. In what time will the reaction be 80% complete ?

Explanation

(i) Let `A=100 M, [A_(0)]-[A]=20 M`,
For the zero order reaction
`k=(([A_(0)]-[A])/(t))`
`k=((20M)/("20 min"))="1 M min"^(-1)`
Rate constant for a reaction `= "1 M min"^(-1)`
(ii) To calculate the time for 80% of completion
`k = "1 M min"^(-1), [A_(0)]=100 M`,
`[A_(0)]-[A]=80 M, t = ?`
Therefore,
`t=(([A_(0)]-[A])/(k))=((80 M)/("1 M min"^(-1)))=80` min.