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?

Answer»

`399` min
`410` min
`250` min
`120` min

Solution :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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