#### 12th Standard Chemistry English Medium Chemical Kinetics Reduced Syllabus Important Questions 2021

12th Standard

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Chemistry

Time : 01:00:00 Hrs
Total Marks : 100

Multiple Choice Questions

15 x 1 = 15
1. For a first order reaction A ⟶ B the rate constant is x min−1. If the initial concentration of A is 0.01M , the concentration of A after one hour is given by the expression.

(a)

001. e−x

(b)

1 x 10-2(1-e-60x)

(c)

(1x10-2)e-60x

(d)

none of these

2. The addition of a catalyst during a chemical reaction alters which of the following quantities? (NEET)

(a)

Enthalpy

(b)

Activation energy

(c)

Entropy

(d)

Internal energy

3. Consider the following statements :
(i) increase in concentration of the reactant increases the rate of a zero order reaction.
(ii) rate constant k is equal to collision frequency A if Ea = 0
(iii) rate constant k is equal to collision frequency A if Ea =0
(iv) a plot of ln (k) vs T is a straight line.
(v) a plot of ln (k) vs $\left( \cfrac { 1 }{ T } \right)$ is a straight line with a positive slope.
Correct statements are

(a)

(ii) only

(b)

(ii) and (iv)

(c)

(ii) and (v)

(d)

(i), (ii) and (v)

4. Which of the following statement is not correct?

(a)

Molecularity of a reaction cannot be fractional

(b)

Molecularity of a reaction cannot be more than three

(c)

Molecularity of a reaction can be zero

(d)

Molecularity is assigned for each elementary step of mechanism.

5. For an exothermic chemical process occurring in 2 steps as
(i) A +B ⟶ X (slow) ;
(ii) X ⟶  AB (fast)
The progress of the reaction can be best described by (x- intermediate).

(a)

(b)

(c)

(d)

None of these

6. During a chemical reaction, the concentration of reaction

(a)

increases

(b)

decreases

(c)

remains constant

(d)

first increases and then decreases

7. The half life period of a first order reaction is 10 minutes. Then its rate constant is

(a)

6.93 x 102 min-1

(b)

0.693 x 10-2 min-1

(c)

6.932 x 10-2 min-1

(d)

69.3 x 10-1 min-1

8. If the activation energy is high) then the rate of the reaction is

(a)

high

(b)

moderate

(c)

low

(d)

cannot be predicted

9. Rate law cannot be determined from balanced chemical equation if _____________

(a)

Reverse reactions is not involved

(b)

It is an elementary reaction

(c)

It is a sequence of elementary reactions

(d)

All of the reactants is in excess. Rate law can be determined from balanced chemical equation if it is an elementary reaction.

10. The value of rate constant of a pseudo first order reaction________________

(a)

Independent on the concentration of reactants present in small amount

(b)

Depends on the concentration of reactants present in excess

(c)

Independent of the concentration of reactants

(d)

Depends only on temperature.

11. By the order of reaction we mean _______________

(a)

the sum of powers to which the concentration terms are raised in the rate equation

(b)

the number of reactants take part in the reaction

(c)

the number of concentration terms in the velocity equation for the reaction

(d)

the least number of product molecule needed for the reaction

12. For a reaction 2A + B ⟶ 3C, express the rate of reaction in terms of formation of the product _____________

(a)

$\frac { 1 }{ 2 } \frac { d\left[ A \right] }{ dt }$

(b)

$\frac { -1 }{ 3 } \frac { d\left[ C \right] }{ dt }$

(c)

$\frac { 1 }{ 3 } \frac { d\left[ C \right] }{ dt }$

(d)

$\frac { -1 }{ 2 } \frac { d\left[ B \right] }{ dt }$

13. The minimum energy that all colliding molecules must possess so as to make the collisions more effective and successful is_____________

(a)

activation energy

(b)

colliding energy

(c)

threshold energy

(d)

kinetic energy

14. The time required for 50%completion of the reaction is known as ___________

(a)

Average life period

(b)

Half-life period

(c)

Rate

(d)

None of these

15. If [A] is the concentration of A at any time t and [Ao]is the concentration at t = 0, then for the first order reaction, the rate equation can be written as _________

(a)

$k=\frac { 2.303 }{ t } \log { \left[ \frac { A }{ { A }_{ 0 } } \right] }$

(b)

${ k }_{ t }=2.303\log { \left[ \frac { { A }_{ 0 } }{ \left[ A \right] } \right] }$

(c)

$k=2.303\log { \left[ \frac { { A }_{ 0 } }{ \left[ { A }_{ 0 } \right] -\left[ A \right] } \right] }$

(d)

$k=\frac { 2.303 }{ t } \log { \left[ \frac { { A }_{ 0 } }{ { A } } \right] }$

1. 2 Marks

10 x 2 = 20
16. Define average rate and instantaneous rate

17. What is an elementary reaction? Give the differences between order and molecularity of a reaction

18. Describe the graphical representation of first order reaction.

19. The rate law for a reaction of A, B and C has been found to be rate =k[A]2[B][L]3/2 How would the rate of reaction change when
(i) Concentration of [L] is quadrupled
(ii) Concentration of both [A] and [B] are doubled
(iii) Concentration of [A] is halved
(iv) Concentration of [A] is reduced to $\left( 1/3 \right)$ and concentration of [L] is quadrupled.

20. What is the study of chemical kinetics used for?

21. Why is instantaneous rate preferred over average rate?

22. The decomposition reaction of ammonia gas on platinum surface has a rate constant R = 2.5 x 10-4mol L-1. What is the order of the reaction.

23. How does the value of rate constant vary with reactant constant.

24. Consider the oxidation of nitric oxide to form NO2
2NO(g) + O2(g) ➝2NO (g)
(a). Express the rate of the reaction in terms of changes in the concentration of NO,O2 and NO2.
(b). At a particular instant, when [O2] is decreasing at 0.2 mol L−1s−1 at what rate is [NO2] increasing at that instant?

25. The rate of the reaction X+2y⇾ product is 4x10-3 mol L-1S-1, if [X]=[Y]=0.2M and rate constant at 400K is 2x10-2s-1, What is the overall order of the reaction

1. 3 Marks

10 x 3 = 30
26. For a reaction x+y+z$\longrightarrow$ productsthe rate law is given by ratek =k[x]3/2[y]1/2 what is the overall order of the reaction and what is the order of the reaction with respect to z.

27. Explain briefly the collision theory of bimolecular reactions

28. The decomposition of Cl2O7 at 500K in the gas phase to Cl2 and O2 is a first order reaction. After 1 minute at 500K, the pressure of Cl2O7 falls from 0.08 to 0.04 atm. Calculate the rate constant in s-1

29. Identify the order for the following reactions
(i) Rusting of Iron
(ii) Radioactive disintegration of 92U238
(iii) $2A+3B\longrightarrow products$;rate k[A]1/2[B]2

30. (i) Molecularity of any reaction is not equal to zero. Why?
(ii) For which type of reactions, order, and molecularity have the same value?

31. The rate constant, the activation energy and frequency factor of a chemical reaction at 25oC are 3.0 x 10-4 S-1; 104.4 kJ mol-1  and 6.0 x 1014 S-1 respectively. What is the value of the rate constant when T ⟶ ∞?

32. A first order reaction is found to have a rate A constant k = 7.39 x 10-5 S-1. Find the half life of this reaction.

33. A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is
(i) doubled (ii) reduced to half

34. A reaction is first order in A and second order in B.
(i) Write the differential rate equation.
(ii) How is rate affected on increasing the concentration of B three times?
(iii) How is the rate affected when the concentrations of both A and Bare doubled?

35. Show that in case of first order reaction, the time required for 99.9% completion is nearly ten times the time required for half completion of the reaction.

1. 5 Marks

7 x 5 = 35
36. The rate constant for a first order reaction is 1.54 x 10-3 s-1. Calculate its half life time.

37. A zero order reaction is 20% complete in 20 minutes. Calculate the value of the rate constant. In what time will the reaction be 80% complete?

38. In a pseudo first order hydrolysis of ester in water, the following results were obtained.

1 0 30 60 90
[Ester]mol L-1 0.55 0.31 0.17 0.085

(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(i) Calculate the pseudo first order rate constant for the hydrolysis of ester.

39. Write an account of the Arrhenius equation for rates of chemical reactions.

40. The conversion of molecules x to y follows second order kinetics. Its concentration of x is increased to three times how will it affect the rate of formation of y?
For the reaction x ➝ y as it follows second order kinetics wherefore the rate of formation of y?

41. The specific reaction. rates of a chemical reaction are 2.45 x 10-5 sec-1 at 273 K and 16.2 x10-4 sec-1 at 303 K. Calculate the activation energy.

42. Rate constant of a first order reaction is 0.45 sec-1, calculate its half life.