1.

A first-order reaction is half completed in 45 minutes. How long does it need 99.9% of the reaction to be completed

Answer»

`5` HOURS
`7.5` hours
`10` hours
`20` hours

Solution :`k = (0.963)/(45) "min"^(-1) = (2.303)/(t_(99.9%))"log"(a)/(a-0.999)`
or `t_(99.9%) = (2.303 xx 45)/(0.693) log10^(3) = 448min ~~ 7.5 hr`


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