Chemical Kinetics Question 178

Question: A First order reaction is half completed in 45 minutes. How long does it need 99.9% of the reaction to be completed [AIIMS 2001]

Options:

A) 5 hours

B) 7.5 hours

C) 10 hours

D) 20 hours

Show Answer

Answer:

Correct Answer: B

Solution:

$ k=\frac{0.693}{45}{{\min }^{-1}}=\frac{2.303}{{t_{99.9}}}\log \frac{a}{a-0.999a} $ or

$ {t_{99.9}}=\frac{2.303\times 45}{0.693}\log 10^{3}=448\min \approx 7.5hrs $



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