NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions
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Question : 18
Total: 39
For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.
Solution:
99% x = 99 % [ R 0 ]
or,[ R ] = [ R 0 ] − 0.99 [ R 0 ]
= 0.01 [ R 0 ]
For first order reaction,t =
log
∴ t 99 % =
log
=
log 10 2 = 2 ×
90% [ R ] = [ R 0 ] − 0.90 R 0 ]
= 0.1 [ R 0 ]
∴ t 90 % =
log
=
log 10 =
∴
= (
) ∕ (
) = 2
or,t 99 % = 2 × t 90 %
or,
For first order reaction,
90
or,
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