Engineering Chemistry Multiple Choice Questions on “Integrated Rate Equation and Half Lives”.
1. For a zero order reaction, the rate of reaction is independent of ___________
a) Temperature
b) Nature of reactants
c) Concentration of reactants
d) Effect of catalyst
Answer: c
Clarification: For a zero order reaction, the rate of reaction is independent of the concentration of reactants. The rate law for a zero order reaction is R = K.
2. The half-life period of zero order reaction is directly proportional to the ___________
a) Rate constant
b) Initial concentration of reactants
c) Final concentration of reactants
d) Concentration of products
Answer: b
Clarification: The half-life period of zero order reaction is directly proportional to the initial concentration of reactants. It is given by:
t1/2 = [A0] / 2K .
3. Which of the following is not an example of zero order reaction?
a) Photochemical combination of hydrogen and chlorine
b) Decomposition of ammonia over molybdenum surface
c) Thermal decomposition of HI on gold surface
d) Inversion of cane sugar in the presence of mineral acids
Answer: d
Clarification: Inversion of cane sugar in the presence of mineral acids is not an example of zero order reaction. All the other options are the example of zero order reaction.
4. For a first order reaction, the half life period is independent of the ___________
a) Initial concentration of the reactants
b) Final concentration of the reactants
c) Rate constant
d) Concentration of products
Answer: a
Clarification: For a first order reaction, the half life period is independent of the initial concentration of the reactants. t1/2 = ln2 / K .
5. The thermal decomposition of nitrogen pentaoxide in the gaseous phase is the example of ___________
a) Zero order reaction
b) Half order reaction
c) First order reaction
d) Second order reaction
Answer: c
Clarification: The thermal decomposition of nitrogen pentaoxide in the gaseous phase is the example of first order reaction. A first order reaction depends on the concentration of only one reactant (a unimolecular reaction).
6. A compound decomposes according to the first order rate law with a half life period of 30 min. What will be the fraction of the remaining compound after 120 min?
a) 0.625
b) 0.0625
c) 0.25
d) 0.025
Answer: b
Clarification: k = 0.693/t1/2
K = (2.303/t) log ([R0]/[Rt]).
7. In a first order reaction, the time required for the completion of 99% is _______ for its 90% completion.
a) Same
b) Negligible
c) Thrice
d) Twice
Answer: d
Clarification: In a first order reaction, the time required for the completion of 99% is twice for its 90% completion. ln [A] = -kt + ln [A0].
8. In a first order reaction, the time required for the completion of 99% is _______ times the time required for the completion of half of the reaction.
a) 5
b) 10
c) 20
d) 50
Answer: b
Clarification: In a first order reaction, the time required for the completion of 99% is ten times the time required for the completion of half of the reaction. ln [A] = -kt + ln [A0].
9. The half life period of first order reaction is 15 min. Its rate constant will be equal to ___________
a) 0.0462 min-1
b) 0.462 min-1
c) 0.00462 min-1
d) 0.562 min-1
Answer: a
Clarification: k = 0.693/t1/2
10. For a second order reaction, the rate is proportional to the square root of the concentration of the same reactant.
a) True
b) False
Answer: b
Clarification: For a second order reaction, the rate is proportional to the square of the concentration of the same reactant.
11. Which of the following is not an example of second order reaction?
a) Oxidation of hydrogen bromide
b) Saponification of ester
c) Acid catalyzed hydrolysis of ester
d) Gaseous decomposition of hydrogen iodide
Answer: c
Clarification: Acid catalyzed hydrolysis of an ester is not an example of second order reaction. All the other options are examples of second order reaction.
12. The half life period of nth order reaction varies inversely to ____________ th power of the initial concentration of the reactants.
a) n
b) 2n
c) (n+1)
d) (n-1)
Answer: d
Clarification: The half life period of nth order reaction varies inversely to (n-1) th power of the initial concentration of the reactants. The half-life of a reaction describes the time needed for half of the reactant to be depleted.
13. The order of the reaction, if the time of half-completion is changed from 50 sec to 25 sec, when the initial concentration is changed from 0.5 to 1M will be ___________
a) 0
b) 1
c) 2
d) 3
Answer: c
Clarification: Tb / Ta = (a/b)n-1