Rate of reaction factors order molecularity and rate laws - Question Bank

1. The term 'rate-determining step' in a reaction mechanism refers to:
A) The fastest step in the mechanism.
B) The slowest step in the mechanism.
C) The step with the highest activation energy.
D) The step with the lowest activation energy.
2. If doubling the concentration of a reactant A increases the rate of reaction by a factor of 8, the order with respect to A is:
A) 1
B) 2
C) 3
D) 4
3. For an elementary reaction, the rate law can be written by directly observing the stoichiometric coefficients of the reactants. This statement is:
A) True
B) False
C) True only for unimolecular reactions
D) True only for bimolecular reactions
4. The rate of a reaction decreases as temperature decreases because:
A) The activation energy increases.
B) The number of effective collisions decreases.
C) The concentration of reactants decreases.
D) The molecularity of the reaction decreases.
5. For the rate law Rate = k[A]^1[B]^0, what is the overall order of the reaction?
A) 0
B) 1
C) 2
D) Cannot be determined
6. For a reaction A + B -> Products, if Rate = k[A]^1[B]^0, what is the order with respect to B?
A) 0
B) 1
C) 2
D) Cannot be determined
7. If the rate of a reaction is independent of the concentration of all reactants, the order is:
A) Zero
B) First
C) Second
D) Third
8. What is the molecularity of the reaction 2A -> B, assuming it is an elementary reaction?
A) 0
B) 1
C) 2
D) 3
9. Consider the reaction 2A -> B. If the rate law is Rate = k[A]^2, what is the order with respect to A?
A) 0
B) 1
C) 2
D) 3
10. Which of the following is a characteristic of the order of reaction?
A) It is always an integer.
B) It is determined from the stoichiometry of elementary steps.
C) It is determined experimentally.
D) It cannot be zero.
11. Which of the following is a characteristic of molecularity?
A) It is always an integer.
B) It can be zero or fractional.
C) It is determined experimentally.
D) It changes with temperature.
12. For a complex reaction, the molecularity of the rate-determining step is:
A) Equal to the overall order of the reaction.
B) Not necessarily equal to the overall order of the reaction.
C) Always zero.
D) Always one.
13. If the rate of reaction is R = k[A]^1.5, the order of the reaction is:
A) 1
B) 1.5
C) 2.5
D) 3
14. The unit of the rate constant for a third-order reaction is:
A) mol L⁻¹ s⁻¹
B) L mol⁻¹ s⁻¹
C) L² mol⁻² s⁻¹
D) s⁻¹
15. A catalyst increases the rate of a reaction by:
A) Increasing the activation energy.
B) Decreasing the activation energy.
C) Increasing the concentration of reactants.
D) Decreasing the temperature.
16. In the Arrhenius equation, Ea represents:
A) The frequency factor
B) The activation energy
C) The gas constant
D) The absolute temperature
17. What is the relationship between the rate constant (k) and temperature (T) described by the Arrhenius equation?
A) k = A * e^(-Ea/RT)
B) k = A + e^(Ea/RT)
C) k = A / e^(Ea/RT)
D) k = A - e^(-Ea/RT)
18. The rate of a reaction generally increases with an increase in temperature because:
A) The activation energy decreases.
B) The number of effective collisions increases.
C) The concentration of reactants increases.
D) The molecularity of the reaction increases.
19. For the reaction A + 2B -> C with rate law Rate = k[A][B]^2, the overall order is:
A) 1
B) 2
C) 3
D) 4
20. For a reaction A + 2B -> C, if the rate law is Rate = k[A][B]^2, the order with respect to A is:
A) 1
B) 2
C) 3
D) 0
21. Which of the following statements about the rate constant 'k' is correct?
A) It depends on the concentration of reactants.
B) It depends on the temperature.
C) It is independent of the nature of reactants.
D) It is independent of the presence of a catalyst.
22. The rate of reaction is expressed as Rate = k[A]^0. This means the reaction is:
A) First order
B) Second order
C) Zero order
D) Third order
23. What is the molecularity of the reaction A + B -> Products, if it occurs in a single step?
A) 1
B) 2
C) 3
D) Cannot be determined
24. In the mechanism A + B -> C (slow), C + D -> E (fast), what is the order of the reaction with respect to B?
A) 0
B) 1
C) 2
D) 3
25. Consider the reaction mechanism: Step 1: A + B -> C (slow) Step 2: C + D -> E (fast). What is the order of the reaction with respect to A?
A) 0
B) 1
C) 2
D) 3
26. If a reaction is bimolecular, its molecularity is:
A) 1
B) 2
C) 3
D) Cannot be determined
27. For the reaction H2 + I2 -> 2HI, the rate law is found to be Rate = k[H2][I2]. What is the order of this reaction?
A) 1
B) 2
C) 3
D) 4
28. The rate of a reaction is halved when the concentration of a reactant is halved. This indicates the order with respect to that reactant is:
A) Zero
B) First
C) Second
D) Cannot be determined
29. Which factor generally increases the rate of a reaction significantly?
A) Decreasing concentration
B) Increasing temperature
C) Adding an inert substance
D) Decreasing pressure
30. For the rate law Rate = k[A][B]², what is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
31. A reaction has a rate law Rate = k[A][B]². What is the order with respect to B?
A) 1
B) 2
C) 3
D) 4
32. What is the unit of the rate constant for a second-order reaction?
A) s⁻¹
B) mol L⁻¹ s⁻¹
C) L mol⁻¹ s⁻¹
D) L² mol⁻² s⁻¹
33. In the reaction 2NO(g) + O2(g) -> 2NO2(g), if the rate law is Rate = k[NO]^2, what is the overall order of the reaction?
A) 0
B) 1
C) 2
D) 3
34. Consider the reaction: 2NO(g) + O2(g) -> 2NO2(g). If the rate law is Rate = k[NO]^2, what is the order of the reaction with respect to O2?
A) 0
B) 1
C) 2
D) 3
35. Which of the following statements is true about order and molecularity?
A) Order can be fractional, molecularity cannot.
B) Molecularity can be fractional, order cannot.
C) Both can be fractional.
D) Neither can be fractional.
36. For an elementary reaction, the order of the reaction is equal to its:
A) Molecularity
B) Activation energy
C) Rate constant
D) Stoichiometric coefficient
37. The rate law for a reaction can be determined experimentally, while molecularity can be determined:
A) From the balanced chemical equation for elementary reactions.
B) From the balanced chemical equation for complex reactions.
C) Only experimentally.
D) From the overall stoichiometry.
38. For a complex reaction, the rate law is determined by:
A) The slowest step (rate-determining step).
B) The fastest step.
C) The sum of all steps.
D) The stoichiometry of the overall reaction.
39. Can molecularity be zero?
A) Yes
B) No
C) Only for complex reactions
D) Only for elementary reactions
40. Can molecularity be a fractional value?
A) Yes
B) No
C) Only for complex reactions
D) Only for elementary reactions
41. What is the molecularity of the elementary reaction 2A + B -> C?
A) 1
B) 2
C) 3
D) 4
42. Molecularity of a reaction is defined for:
A) Elementary reactions only
B) Complex reactions only
C) Both elementary and complex reactions
D) Overall reactions
43. Which of the following units is appropriate for the rate constant of a first-order reaction?
A) L mol⁻¹ s⁻¹
B) mol L⁻¹ s⁻¹
C) s⁻¹
D) L² mol⁻² s⁻¹
44. For a zero-order reaction, the rate is:
A) Independent of the concentration of reactants.
B) Directly proportional to the concentration of reactants.
C) Inversely proportional to the concentration of reactants.
D) Proportional to the square of the concentration of reactants.
45. If the concentration of a reactant is doubled and the rate of reaction quadruples, what is the order of the reaction with respect to that reactant?
A) Zero
B) First
C) Second
D) Third
46. What does the rate constant 'k' represent?
A) The proportionality constant relating rate to concentrations.
B) The total amount of reactants consumed.
C) The time required for half the reaction to complete.
D) The activation energy of the reaction.
47. The overall order of the reaction Rate = k[A]^x[B]^y is:
A) x
B) y
C) x + y
D) 1
48. For a reaction A + B -> Products, the rate law is given by Rate = k[A]^x[B]^y. What is the order of the reaction with respect to A?
A) x
B) y
C) x + y
D) 1
49. Which of the following is NOT a factor affecting the rate of a chemical reaction?
A) Concentration of reactants
B) Temperature
C) Nature of reactants
D) Number of moles of product formed
50. What is the rate of reaction?
A) The change in concentration of a reactant or product per unit time.
B) The time taken for a reaction to complete.
C) The maximum amount of product that can be formed.
D) The energy required to initiate a reaction.
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