A first order reaction is 20% complete in 20 minuts. Calculate the time it will take the reaction to complete 80%.

Explanation

Step 1: To calculate k
`[R]_0=100(say),[R]=100-20=80`
t=20 min, k=?
`k=(2.303)/(t)log([R]_0)/([R])`
`=(2.303)/("20 min")log(100)/(80)`
`=(2.303)/("20 min")[log10-log8]`
`=(2.303)/("20 min")[1-0.9031]`
`=(2.303xx0.0969)/("20 min")`
`=0.011 min^(-1)`
Step II : To calculate t
`[R]_0=100,[R]=100-80=20`
k=0.01, 1 `min^(-1)`
`t=(2.303)/(k)log([R]_0)/([R])`
`=(2.303)/(0.0111" min"^(-1))log(100)/(20)`
`=(2.303)/(0.0111" min"^(-1))log5`
`=(2.303)/(0.0111" min"^(-1))xx0.699`
=145 min.