1.

75% of a first-order reaction was completed in 32 minutes. When was 50% of the reaction completed

Answer»

`24` min
`4` min
`16` min
`8` min

Solution :LET original amount, `N_(0) = 100`
Since `75%` COMPLETED, so final amount `N = 100 - 75 = 25`
As we know
`(N_(0))/(N) = 2^(n)`,where `n =` no. of half LIVES
or,`(100)/(25) = 2^(n)`
or,`4 = 2^(n)` or, `2^(2)` or, `2^(2) = 2^(n)`
`:. n=2`
Since total time `= n xx t_(1//2)`
`32` minutes `= 2 xx t_(1//2)`
`:. t_(1//2) = 16` minutes


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