Question

25% of first order reaction is completed in 30 minutes. Calculate the time taken in minutes for the reaction to go to 90% completion. 

Answer 1

t = 30 min
[A]₀ = 100 
[A]_{1 = 75}

<sub>∴ `k = (2.303)/tlog  [A]_0/[A]_1`

`therefore k = 2.303/30 log  100/75`
`therefore k = 0.076xx0.1249=9.58 xx 10^-3`
Now, time requried for 90% completion 
t = ?</sub>
`[A]_0= 100`

`[A]_1 = 10`
k = 9.58 × 10^-1 
`9.58 × 10^-3 =2.303/t  log  100/10 ` 
_{`t = 204.39 min`}