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 = (0.693)/(45) "min"^(-1) = (2.303)/(t_(99.9%)) "log" (a)/(a-0.999 a)` or
`t_(99.9%) = (2.303 XX 45)/(0.693) "log" 10^(3) = 448` min = 7.5 hrs.


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