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kherson [118]
3 years ago
10

A reactant decomposes with a half-life of 29.5 s when its initial concentration is 0.229 M. When the initial concentration is 0.

639 M, this same reactant decomposes with a half-life of 82.3 s. What is the value and unit of the rate constant for this reaction?
Chemistry
1 answer:
Dmitrij [34]3 years ago
4 0

Answer :

The order of reaction is, 0 (zero order reaction).

The value of rate constant is, 0.00388Ms^{-1}

Explanation :

Half life : It is defined as the time in which the concentration of a reactant is reduced to half of its original value.

The general expression of half-life for nth order is:

t_{1/2}\propto \frac{1}{[A_o]^{n-1}}

or,

\frac{t_{1/2}_1}{t_{1/2}_2}=\frac{[A_2]^{n-1}}{[A_1]^{n-1}}

or,

n=\left(\frac{\log\frac{(t_{1/2})_1}{(t_{1/2})_2}}{\log\frac{(A)_2}{(A)_1}}\right )+1           .............(1)

where,

t_{1/2} = half-life of the reaction

n = order of reaction

[A] = concentration

As we are given:

Initial concentration of A = 0.229 M

Final concentration of A = 0.639 M

Initial half-life of the reaction = 29.5 s

Final half-life of the reaction = 82.3 s

Now put all the given values in the above formula 1, we get:

n=\left (\frac{\log \frac{29.5}{82.3}}{\log\frac{0.639}{0.229}}\right )+1

n=0.000196\approx 0

Thus, the order of reaction is, 0 (zero order reaction).

Now we have to determine the rate constant.

To calculate the rate constant for zero order the expression will be:

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

When,

t_{1/2} = 29.5 s

[A_o] = 0.229 M

29.5s=\frac{0.229M}{2k}

k=0.00388Ms^{-1}

Thus, the value of rate constant is, 0.00388Ms^{-1}

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