Chemical Kinetics - Result Question 44

####44. A substance ‘A’ decomposes by a first order reaction starting initially with [A]=2.00m and after 200min, [A] becomes 0.15m. For this reaction t1/2 is

(a) 53.72min

(b) 50.49min

(c) 48.45min

(d) 46.45min

[1995]

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Solution:

  1. (a) Given initial concentration (a)=2.00m; Time taken (t)=200min and final concentration (ax)=0.15m. For a first order reaction, rate constant,

k=2.303tlogaax=2.303200log2.000.15 =2.303200×(0.301+0.824)=1.29×102min1.

Further

(t1/2)=0.693k=0.6931.29×102=53.49min.



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