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If the half life of a first order reaction is 6.93 minutes then the time required for completion of 99% of the reaction will be _______ minutes. (Given: log 2 = 0.3010)
Correct Answer: 46.06
Step 1: Calculate the rate constant $$(k)$$.
For, first order reaction the rate constant $$(k)$$ is related to $$t_{1/2}$$ by this formula:
$$t_{1/2}=\frac{0.693}{k}$$
since,
$$t_{1/2}=6.93$$
$$k=\frac{0.693}{6.93}=0.1\ \min^{-1}$$
Step 2: Calculate time for 99% Completion
The integrated rate law for a first-order reaction give us to solve for time $$(t)$$:
$$t=\frac{2.303}{k\ }\log\left(\frac{\left[A_o\right]}{\left[A_t\right]}\right)$$
For 99% completion, 1% of the reactant remains.
Let's assume the initial concentration $$[A]_0 = 100$$, then the final concentration $$[A]_t = 1$$:
$$t=\frac{2.303}{0.1}\log\left(\frac{100}{1}\right)$$
$$t=\frac{2.303}{0.1}\times\ 2$$
$$t=23.03\times\ 2$$
$$t=46.06$$ minutes
Therefore, the time required for completion of 99% of the reaction will be 46.06 minutes.
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