Nuclear Chemistry - Result Question 1

####1. The half life of a substance in a certain enzyme catalysed reaction is 138s. The time required fo the concentration of the substance to fall fron 1.28mgL1 to 0.04mgL1, is :

[2011]

(a) 414s

(b) 552s

(c) 690s

(d) 276s

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Solution:

  1. (c) For a first order reaction

Total time T= no. of half lives (n)× half life (t1/2)

NN0=(12)n

where n= no. of half lives

Give N0 (original amount) =1.28mg/l

N (amount of substance left after time T )

=0.04mgL1

0.041.28=(12)n;132=(12)n;(12)5=(12)nn=5T=5×138=690



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