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 $
