A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed. (Given : log 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)

 

 

 

 
 
 
 
 

Answers (1)
S Sumit

Order = 1
k= \frac{2\cdot 303}{t}\log \frac{a}{a-x}
25% decomposition , x= 0\cdot 25a, t= 20\, min
k= \frac{2\cdot 303}{20}\log \frac{a}{a-0\cdot 25a}
k= \frac{2\cdot 303}{20}\log \frac{1}{0\cdot 75}
k= \frac{2\cdot 303}{20} \left ( \log4-\log3 \right )
k= 0\cdot 01439\, min^{-1}
75 % decomposition , t = ? , x= 0\cdot 75a
t=\frac{2\cdot 303}{0\cdot 0144}\log\frac{a}{a-0\cdot 75a}
t=\frac{2\cdot 303}{0\cdot 0144}\log\frac{1}{0\cdot25}
t=\frac{2\cdot 303}{0\cdot 0144}\log4
t=\frac{2\cdot 303}{0\cdot 0144}\times 0\cdot 6021
= 96\cdot 3\, min

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