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
