A first order reaction is 60% complete in 20 minutes .How long will the reaction take to be 84% complete ?

Options

A. 54 mins
B. 68 mins
C. 40 mins
D. 76 mins

Answer

C

Explanation

( C) For 60% completion of reaction
`k= (2.303)/(t) "log"([R]_(0))/([R])`
`=(2.303)/(20)"log" (100)/(40)`
`=0.045 "min^(-1)`
For 84 % completion of reaction
`t = (2.303)/(k)"log"([R]_(0))/([R])`
`=(2.303)/(0.045)"log"(100)/(16)`
=40.7 min