1.

Thermal decomposition of a compound is of first order. If `50%` of a sample of the compound is decomposed in `120` minutes how long will it take for `90%` of the compound to decompose?A. `399` minB. `410` minC. `250` minD. `120` min

Answer» Correct Answer - A
First calculate the values of `K`
`K = (0.693)/(T_(1//2)) = (0.693)/(120) = 5.77 xx 10^(3) min-1`
Now we know that for a first order reaction
`K = (2.303)/(t) "log"((a)/(a-x))`
Here the initial concentratiion `a = 100` and `n = 90`
`:. 5.77 xx 10^(-3) = (2.303)/(t) "log"(100)/(100-90)`
`t = (2.303)/(5.77 xx 10^(-3))"log"((a)/(a-x))`
Solving, `t = 399` minute


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