1. Calculate the half-life for N2O5 at 25oC and the fraction decomposed after 8 hours (k = 3.38 x 10-5 s-1).
Solution
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Hence,
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2. Zinc-65 has a half-life of 245 days (a) What % of the original activity remains after 100 days? (b) How much
time is required for the activity to reduce to 5% of the initial activity?
Solution
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Therefore,
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Therefore,
3. At 25°C the half-life for the decomposition of N2O5 is 2.05 x 104 s and is independent of the initial
concentration of N2O5. (a) What is the order of the reaction? (b) What length of time is required for 80% of the
N2O5 to decompose?
Solution
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4. Determine the half-life of a zero-order reaction if the original concentration of the reactant is 1.2 mol dm-3 and
k0 is 0.00625 mol dm-3 s-1.
Solution
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5. A reaction has a rate law of the form k[A]2[B]. what are the units of the rate constant k if the rate was
measured in mol dm-3 s-1?
Solution
The unit of concentration is mol dm-3
[ ] [ ]
[ ] [ ]
6. The half-life of carbon is 5700 years (a) What % of the original activity remains after 100 years? (b) How
much time is required for the activity to decrease to 5% of the initial value?
Solution
(a) The decay constant (λ) can be obtained from the equation t1/2 = 0.693/λ, therefore,
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From the rate law,
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