Q.

The half-life of a first order reaction is 100 seconds. What is the time required for 90 % completion of the reaction?
 

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a

100 sec.
 

b

339 sec.
 

c

500 sec.
 

d

200 sec.
 

answer is C.

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Detailed Solution

Half life time t12=100sec. (given) K=0.693100

Time required for 90% completion?
Here let initial concentration =a
Concentration decomposed is 90 %
 x=90×a100 =0.9a
Now,

t=2.3030.693t1/2logaax 2.303100logaa0.9a 2.3030.693loga0.1a 2.303100log10 2.3030.693×100×log10 339.32sec

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