# Topic: Unit VII: Chemical Kinetics (Test 3)

Topic: Unit VII: Chemical Kinetics
Q.1
In a homogeneous reaction A →B + C + D , the initial pressure was P0 and after time t it was P. expression for rate constant in terms of P0, P and t will be
A. B. C. D. Explaination / Solution: Workspace
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Q.2
If 75% of a first order reaction was completed in 60 minutes , 50% of the same reaction under the same conditions would be completed in
A. 20 minutes
B. 30 minutes
C. 35 minutes
D. 75 minutes
Explaination / Solution:

t75% = 2t50%

t50% = (t75% / 2) = (60/2) = 30 min

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Q.3
The half life period of a radioactive element is 140 days. After 560 days , 1 g of element will be reduced to
A. (1/2)g
B. (1/4)g
C. (1/8)g
D. (1/16)g
Explaination / Solution:

In 140 days initial concentration reduced to (1/2)g

In 280 days initial concentration reduced to (1/4)g

In  420 days initial concentration reduced to (1/8)g

In 560 days initial concentration reduced to (1/16)g

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Q.4
The correct difference between first and second order reactions is that
A. A first order reaction can be catalysed; a second order reaction cannot be catalysed.
B. The half life of a first order reaction does not depend on [A0]; the half life of a second order reaction does depend on [A0].
C. The rate of a first order reaction does not depend on reactant concentrations; the rate of a second order reaction does depend on reactant concentrations.
D. The rate of a first order reaction does depend on reactant concentrations; the rate of a second order reaction does not depend on reactant concentrations.
Explaination / Solution:

For a first order reaction

t1/2 = 0.6932/k

For a second order reaction Workspace
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Q.5
After 2 hours, a radioactive substance becomes (1/16)th of original amount. Then the half life ( in min) is
A. 60 minutes
B. 120 minutes
C. 30 minutes
D. 15 minutes 