A first order reaction is `20%` complete in `10 min`. Calculate (a) the specific rate constant of the reaction and (b) the time taken for the reaction to reach `75%` completion.

Explanation

`k = 2.303/t log""(a)/((a-x))`
k = specific reaction rate
Let initial conc. (a) = 100 g, t = 10 min
`:. (a-x) = 80 g`
(`:.` Reactrion is 20% complete)
`k = 2.303/10 log""100/80 =0.0223 "min"^(-1)`
`:.t=2.303/0.0223log""100/25 = 62.18 min`