Chemical Kinetics Question 258

Question: A first order reaction complete its 10% in 20 minutes then time required to complete its 19% is [Kerala CET 2005]

Options:

A) 30 minutes

B) 40 minutes

C) 50 minutes

D) 38 minutes

E) 45 minutes

Show Answer

Answer:

Correct Answer: B

Solution:

In first phase, $ K=\frac{2.303}{20}\log \frac{90}{100} $ …..(i) In second phase $ K=\frac{2.303}{t}\log \frac{81}{100} $ …..(ii) From eq. (i) $ \frac{2.303}{20}\log \frac{90}{100}=\frac{2.303}{t}\log \frac{81}{100} $

$ t=\frac{20(\log 81-\log 100)}{(\log 90-\log 100)} $

$ =\frac{20(1.908-2)}{(1.954-2)}=\frac{20\times (-0.092)}{(-0.046)} $ = 40 minutes



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