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Answer:

[tex]t_{1/2}=30.14\ min[/tex]

Explanation:

Using integrated rate law for first order kinetics as:

[tex][A_t]=[A_0]e^{-kt}[/tex]

Where,  

[tex][A_t][/tex] is the concentration at time t

[tex][A_0][/tex] is the initial concentration

Given:

75 % is decomposed which means that 0.75 of [tex][A_0][/tex] is decomposed. So,

[tex]\frac {[A_t]}{[A_0]}[/tex] = 1 - 0.75 = 0.25

t = 60 min

[tex]\frac {[A_t]}{[A_0]}=e^{-k\times t}[/tex]

[tex]0.25=e^{-k\times 60}[/tex]

k = 0.023 min⁻¹

Considering the expression for half life as:-

[tex]t_{1/2}=\frac {ln\ 2}{k}[/tex]

Where, k is rate constant

So,  

[tex]t_{1/2}=\frac{\ln 2}{0.023}\ min[/tex]

[tex]t_{1/2}=30.14\ min[/tex]

The half-life of a compound if 75% of a given sample of  the compound decomposes in 60 min - 30 min

Given:

t = time of decomposition = 60 minutes

a = let initial amount of the reactant  = 100g

a - x = amount left after decay process = (100-75)g = 25g

Solution:

Expression for rate law for first-order kinetics is given by:

[tex]t=\frac{2.303}{k}\log\frac{a}{a-x}[/tex]

Placing the given values:

[tex]60=\frac{2.303}{k}\log\frac{100}{25}\\\\k=0.023min^{-1}[/tex]

Half-life is the amount of time taken by a radioactive material to decay to half of its original value.

[tex]t_{\frac{1}{2}}=\frac{0.693}{k}t_{\frac{1}{2}}=\frac{0.693}{0.023}\\=30\ min[/tex]

Thus, the half-life of a compound if 75% of a given sample of  the compound decomposes in 60 min - 30 min

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