Chemistry Class 12 Chapter 4

1. When a chemical reaction takes place, during the course of the reaction the rate of reaction

(a) keeps on increasing with time

(b) remains constant with time

(c) keeps on decreasing with time

(d) shows irregular trend with time

Ans (C)

2. The rate of disappearance of SO₂in the reaction, 2SO₂ + O₂ → 2SO₃ is 1.28 x 10^-5 M s^-1. The rate of appearance of SO₃ is …………..

(a) 64 x 10^-5 M s^-1

(b) 0.32 x 10^-5 M s^-1

(c) 2.56 x 10^-5 Ms^-1

(d) 1.28 x 10^-5 M s^-1

Ans (D)

3. In a reaction 2X → Y, the concentration of X decreases from 3.0 moles/litre to 2.0 moles/litre in 5 minutes. The rate of reaction is ………………..

(a) 1 mol L^-1 min^-1

(b) 5 mol L^-1 min^-1

(c) 1 mol L^-1 min^-1

(d) 0.5 mol L^-1 min^-1

Ans (A)

4. The rate constant of a reaction depends upon

(a) temperature of the reaction

(b) extent of the reaction

(c) initial concentration of the reaction

(d) the time of completion of reaction

Ans (A)

5. Rate constant in case of first order reaction is

(a) inversely proportional to the concentration units

(b) independent of concentration units

(c) directly proportional to concentration units

(d) inversely proportional to the square of concentration units

Ans (B)

6. The rate constant for the reaction, 2N₂O₂→ 4NO₂ + O₂ is 2 x 10^–5s^-1. If rate of reaction is 1.4 x 10^-5 mol L^-1 s^-1, what will be the concentration of N₂O₅ in mol L^-1?

(a) 8

(b) 0.7

(c) 1.2

(d) 1

Ans (B)

7. The order of reaction is decided by…………..

(a) temperature

(b) mechanism of reaction as well as relative concentration of reactants

(c) molecularity

(d) pressure

Ans (B)

8. Which of the following is an example of a fraction order reaction ?

(a) NH₄NO₂ → N₂ +2H₂O

(b) NO + O₃ → NO₂+O₂

(c) 2NO + Br₂ → 2NOBr

(d) CH₃CHO → CH₄ + CO

Ans (D)

9. What will be the rate equation for the reaction 2X + Y→ Z, if the order of the reaction is zero ?

(a) Rate = k[X] [Y]

(b) Rate = k

(c) Rate = A[X]⁰[Y]

(d) Rate = k[X][Y]⁰

Ans (B)

10. The unit of rate constant for the reaction, 2H₂+ 2NO → 2H₂O + N₂which has rate – k[H₂][NO]², is …………..

(a) molL^–1s^-1

(b) s^-1

(c) mol^–1L²s^-1

(d) mol L^-1

Ans (C)

11. The unit of rate and rate constant are same for a…………….

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction

Ans (A)

12. The number of molecules of the reactants taking part in a single step of the reaction is indicative of

(a) order of a reaction

(b) molecularity of a reaction

(c) fast step of the mechanism of a reaction

(d) half-life of the reaction

Ans (B)

13. The overall rate of a reaction is governed by

(a) the rate of fastest intermediate step

(b) the sum of the rates of all intermediate steps

(c) the average of the rates of all the intermediate steps

(d) the rate of slowest intermediate step.

Ans (D)

14. Radioactive disintegration is an example of ……………

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction

Ans (B)

15. A first order reaction has a rate constant 1.15 x 10^-3s^-1. How long will 5 g of this reaction take to reduce to 3 g ?

(a) 444 s

(b) 400 s

(c) 528 s

(d) 669 s

Ans (A)

16. Half-life period of a first order reaction is 10 min. What percentage of the reaction will be completed in 100 min ?

(a) 25%

(b) 50%

(c) 99.9%

(d) 75%

Ans (C)

17. The rate constant for a first order reaction is 2 x 10^-2min^-1. The half-life period of reaction is

(a) 69.3 min

(b) 34.65 min

(c) 17.37 min

(d) 3.46 min

Ans (B)

18. The value of rate of a pseudo first order reaction depends upon

(a) the concentration of both the reactants present in the reaction

(b) the concentration of the reactant present in small amount

(c) the concentration of the reactant present in excess

(d) the value of ΔH of the reaction

Ans (B)

19. Under what conditions a bi-molecular reaction may be kinetically of first order ?

(a) When both reactants have same concentration

(b) When one of the reacting species is in large excess

(c) When the reaction is at equilibrium

(d) When the activation energy of reaction is less

Ans (B)

20. For an endothermic reaction, AH represents the enthalpy of the reaction in kj mol^-1. The minimum amount of activation energy will be

(a) less than zero

(b) equal to ΔH

(c) less than ΔH

(d) more than ΔH

Ans (D)

21. The decomposition of a hydrocarbon follows the equation k = (4.5 x 10¹¹ s^-1) e^-28000K/T. What will be the value of activation energy ?

(a) 669 kJ mol^-1

(b) 232.79   kJ mol^-1

(c) 4.5 x 10^-1 kJ mol^-1

(d) 28000 kJ mol^-1

Ans (B)

22. The rate constant is given by the equation k = P.Ze^-Ea/RT Which factor should register a decrease for the reaction to proceed more rapidly ?

(a) T

(b) Z

(c) E

(d) P

Ans (C)

23. Threshold energy is equal to ……………

(a) activation energy

(b) activation energy – energy of molecules

(c) activation energy + energy of molecules

(d) None of these

Ans (C)

24. The role of a catalyst is to change………………..

(a) Gibbs energy of reaction

(b) enthalpy of reaction

(c) activation energy of reaction

(d) equilibrium constant

Ans (C)

25. In the presence of a catalyst, the heat evolved or absorbed during the reaction…………..

(a) increases

(b) decreases

(c) remains unchanged

(d) may increase or decrease

Ans (C)

26. A first order reaction is 50% completed in 1.26 x 10¹⁴How much time would it take for 100% completion ?

(a) 1.26 x 10¹⁵ s

(b) 2.52 x 10¹⁴ s

(c) 2.52 x 10²⁸ s

(d) Infinite

Ans (D)

27. The half life period of first order reaction is 1386 seconds. The specific rate constant of the reaction is

(a) 0.5 × 10^-2 s^-1

(b) 0.5 × 10^-3 s^-1

(c) 5.0 × 10^-2 s^-1

(d) 5.0 × 10^-3 s^-1

Ans (B)

28. The rate constant of a reaction A → B is 0.6 × 10³ mole per second. If the concentration of [A] is 5 M, then what will be concentration of [B] after 20 months?

(a) 0.36 M

(b) 0.72 M

(c) 1.08 M

(d) 3.60 M

Ans (B)

29. Which of the following is affected by catalyst?

(a) ∆H

(b) ∆S

(c) ∆G

(d) Ea

Ans (D)

30. A first order reaction has specific reaction rate 10^-2s^-1. How much time it will take for 20g of reactant to reduce to 5g?

(a) 138.6 s

(b) 346.5 s

(c) 693.0 s

(d) 238.6 s

Ans (A)

31. For a chemical reaction A→B, it is found that the rate of reaction doubles when the concentration of A is increased four times. The order of reaction is

(a) Two

(b) One

(c) Half

(d) Zero

Ans (C

32. The half life of the first order reaction having rate constant K = 1.7 x 10^-5s^-1is

(a) 12.1 h

(b) 9.7 h

(c) 11.3 h

(d) 1.8 h

Ans (C)

33. The rate constant of a reaction depends upon : 

(a) temperature of the reaction

(b) extent of the reaction

(c) initial concentration of the reactants 

(d) the time of completion of reaction

Ans (D)

34. The unit of rate and rate constant are same for a : 

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction 

Ans (A)

35. For a unimolecular reaction : 

(a) the order and molecularity of the slowest step are equal to one

(b) molecularity of the reaction can be zero, one or two

(c) more than one reacting species are involved in one step

(d) molecularity of the reaction can be determined only experimentally 

Ans (A)

36. The overall rate of a reaction is governed by 

(a) the rate of fastest intermediate step

(b) the sum total of the rates of all intermediate steps.

(c) the average of the rates of all the intermediate steps 

(d) the rate of slowest intermediate step

Ans (D)

37. H₂(g) + Cl₂(g) → 2 HCI (g). The order of this reaction is : 

(a) Zero order 

(b) First order

(c) Second order

(d) None of these

Ans (A)

38. For a reaction if activation energies for forward and backward reactions are the same, then :

(a) ΔH = 0

(b) ΔS = 0

(c) The order is zero

(d) None of these

Ans (A)

39. Radioactive disintegration is an example of : 

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction 

Ans (B)

40. t_1/2for first order reaction is : 

(a) 0.6 / k

(b) 0.693 / k

(c) 0.683 / k

(d) 0.10 / k

Ans (B)

41. The rate at which a substance reacts, depends upon its 

(a) Atomic Mass 

(b) Equivalent Mass

(c) Molecular Mass

(d) Active Mass

Ans (D)

42. Half life period of first order reaction is independent of : 

(a) Initial concentration of reactant

(b) Temperature

(c) Pressure

(d) None of these 

Ans (B)