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

1. The rate of a reaction is defined as the rate of disappearance of a reactant or the rate of appearance of a product. For the reaction A -> B, this can be written as:
A) Rate = -d[A]/dt = +d[B]/dt
B) Rate = +d[A]/dt = -d[B]/dt
C) Rate = d[A]/dt = d[B]/dt
D) Rate = -d[A]/dt = -d[B]/dt
2. If the rate of reaction is independent of the concentration of a reactant, it is:
A) First-order with respect to that reactant.
B) Second-order with respect to that reactant.
C) Zero-order with respect to that reactant.
D) Third-order with respect to that reactant.
3. Which of the following units for the rate constant 'k' indicates a third-order reaction?
A) M s⁻¹
B) M⁻¹ s⁻¹
C) M⁻² s⁻¹
D) M⁻³ s⁻¹
4. The rate of a reaction is proportional to the frequency of effective collisions between reactant molecules. This statement is part of:
A) Thermodynamic theory
B) Collision theory
C) Transition state theory
D) Ostwald's dilution law
5. For the reaction 2H₂ + 2NO -> 2H₂O + N₂, if the rate law is Rate = k[H₂][NO]², what is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
6. What is the effect of a catalyst on the equilibrium position of a reversible reaction?
A) Shifts it towards products.
B) Shifts it towards reactants.
C) Does not affect it.
D) Shifts it towards the side with more moles of gas.
7. The Arrhenius equation relates the rate constant to:
A) Concentration and time.
B) Temperature and activation energy.
C) Pressure and volume.
D) Entropy and enthalpy.
8. If the rate of reaction is directly proportional to the concentration of a reactant, it is said to be:
A) Zero-order with respect to that reactant.
B) First-order with respect to that reactant.
C) Second-order with respect to that reactant.
D) Independent of that reactant.
9. The rate law of a reaction provides information about:
A) The overall stoichiometry of the reaction.
B) The mechanism of the reaction.
C) The dependence of the reaction rate on the concentration of reactants.
D) The equilibrium constant of the reaction.
10. For a bimolecular reaction, the molecularity is:
A) 1
B) 2
C) 3
D) Cannot be determined.
11. Which of the following factors has the most significant effect on the rate of a chemical reaction?
A) Pressure (for gaseous reactions)
B) Surface area
C) Concentration
D) Activation energy
12. What is the unit of the rate constant for a first-order reaction?
A) s⁻¹
B) mol L⁻¹ s⁻¹
C) L mol⁻¹ s⁻¹
D) L² mol⁻² s⁻¹
13. For the reaction R -> P, if the rate law is Rate = k[R]⁰, what is the order of the reaction?
A) 0
B) 1
C) 2
D) 3
14. The rate of a reaction is generally increased by:
A) Decreasing the surface area of solid reactants.
B) Increasing the concentration of reactants.
C) Decreasing the temperature.
D) Adding an inhibitor.
15. The collision theory states that for a reaction to occur, reactant molecules must:
A) Have sufficient kinetic energy only.
B) Collide with proper orientation only.
C) Collide with sufficient kinetic energy and proper orientation.
D) Be in a gaseous state.
16. If the half-life of a first-order reaction is 30 minutes, what is the rate constant?
A) 0.0231 min⁻¹
B) 0.01155 min⁻¹
C) 0.693 min⁻¹
D) 30 min⁻¹
17. Which of the following statements about order and molecularity is correct?
A) Order and molecularity are always equal.
B) Order is determined experimentally, while molecularity is theoretical.
C) Molecularity is determined experimentally, while order is theoretical.
D) Both order and molecularity are always equal for complex reactions.
18. The rate constant of a reaction decreases as the temperature increases. This implies:
A) The reaction is exothermic with a high activation energy.
B) The reaction is endothermic with a high activation energy.
C) The reaction is exothermic with a low activation energy.
D) The reaction is endothermic with a low activation energy.
19. For a reaction A + B -> Products, if the rate law is Rate = k[A][B]², what is the overall order of the reaction?
A) 1
B) 2
C) 3
D) 4
20. The rate of reaction is defined as the rate of change of:
A) Concentration of reactants only.
B) Concentration of products only.
C) Concentration of reactants or products.
D) Temperature of the system.
21. What happens to the rate of reaction if the concentration of a reactant involved in a zero-order reaction is doubled?
A) The rate doubles.
B) The rate quadruples.
C) The rate remains unchanged.
D) The rate halves.
22. The unit of the rate constant (k) for a third-order reaction is:
A) s⁻¹
B) mol L⁻¹ s⁻¹
C) L mol⁻¹ s⁻¹
D) L² mol⁻² s⁻¹
23. Which of the following is a characteristic of elementary reactions?
A) They are always multi-step.
B) Their molecularity is equal to their order.
C) Their molecularity is determined experimentally.
D) They do not involve collision theory.
24. What is the order of reaction with respect to reactant A if doubling the concentration of A increases the rate of reaction by a factor of 8?
A) 1
B) 2
C) 3
D) 4
25. The term 'rate-determining step' refers to:
A) The fastest step in a reaction mechanism.
B) The slowest step in a reaction mechanism.
C) The step with the highest activation energy.
D) The equilibrium step in a reaction mechanism.
26. For a first-order reaction, the integrated rate law is given by:
A) [A]t = [A]₀ - kt
B) ln[A]t = ln[A]₀ - kt
C) 1/[A]t = 1/[A]₀ + kt
D) [A]t = [A]₀ * e^(-kt)
27. A catalyst increases the rate of reaction by:
A) Increasing the activation energy.
B) Decreasing the activation energy.
C) Increasing the enthalpy change.
D) Decreasing the enthalpy change.
28. What is the order of the reaction A + B -> Products if the rate law is Rate = k[A]¹/²[B]¹?
A) 1
B) 1.5
C) 2
D) 2.5
29. The rate law for the reaction 2NO(g) + O₂(g) -> 2NO₂(g) is found experimentally to be Rate = k[NO]²[O₂]. What is the molecularity of this reaction?
A) 1
B) 2
C) 3
D) Cannot be determined from the rate law.
30. If a reaction is exothermic and the activation energy for the forward reaction is Ea(f), what is the activation energy for the reverse reaction Ea(r)?
A) Ea(r) = Ea(f) + ΔH
B) Ea(r) = Ea(f) - ΔH
C) Ea(r) = ΔH - Ea(f)
D) Ea(r) = Ea(f)
31. Which of the following is NOT a unit of rate of reaction?
A) mol L⁻¹ s⁻¹
B) M s⁻¹
C) atm s⁻¹
D) mol⁻¹ L s⁻¹
32. For a complex reaction, the rate of reaction is determined by:
A) The fastest step.
B) The slowest step (rate-determining step).
C) The sum of all steps.
D) The equilibrium step.
33. What is the molecularity of a unimolecular reaction?
A) 0
B) 1
C) 2
D) 3
34. The rate law for a reaction can be determined by:
A) Balancing the chemical equation.
B) The stoichiometry of the reaction.
C) Experimental measurements of concentration versus time.
D) The molecularity of the reaction.
35. If the rate of reaction doubles when the temperature is increased by 10°C, what is the approximate temperature coefficient?
A) 1
B) 2
C) 3
D) 4
36. For a second-order reaction, the unit of the rate constant (k) is:
A) s⁻¹
B) mol L⁻¹ s⁻¹
C) L mol⁻¹ s⁻¹
D) L² mol⁻² s⁻¹
37. The activation energy (Ea) of a reaction is:
A) The minimum energy required for reactants to form products.
B) The average kinetic energy of the molecules.
C) The energy released during the reaction.
D) The energy of the activated complex.
38. What is the relationship between the rate constant (k) and temperature (T) described by the Arrhenius equation?
A) k = A * exp(-Ea/RT)
B) k = A + exp(-Ea/RT)
C) k = A / exp(-Ea/RT)
D) k = A - exp(-Ea/RT)
39. A reaction that proceeds in a single step is called:
A) Complex reaction
B) Elementary reaction
C) Photochemical reaction
D) Catalytic reaction
40. For a first-order reaction, the half-life (t₁/₂) is:
A) Independent of the initial concentration.
B) Directly proportional to the initial concentration.
C) Inversely proportional to the initial concentration.
D) Proportional to the square of the initial concentration.
41. Which type of catalyst increases the rate of a reaction?
A) Inhibitor
B) Promoter
C) Positive catalyst
D) Negative catalyst
42. The rate constant 'k' of a reaction is:
A) Dependent on temperature and concentration.
B) Dependent on temperature but independent of concentration.
C) Dependent on concentration but independent of temperature.
D) Independent of both temperature and concentration.
43. What is the unit of the rate constant (k) for a zero-order reaction?
A) s⁻¹
B) mol L⁻¹ s⁻¹
C) L mol⁻¹ s⁻¹
D) L² mol⁻² s⁻¹
44. For the reaction 2A + B -> C, if the rate law is Rate = k[A]^2[B]^1, what is the order of the reaction with respect to A?
A) 0
B) 1
C) 2
D) 3
45. Which of the following statements is true about molecularity?
A) It can be zero or fractional.
B) It is always an integer and usually less than or equal to 3.
C) It is determined experimentally.
D) It applies only to complex reactions.
46. Molecularity of a reaction is defined as:
A) The number of steps in the reaction mechanism.
B) The number of molecules that collide simultaneously with proper energy and orientation to cause a reaction.
C) The sum of the stoichiometric coefficients of the reactants.
D) The order of the reaction.
47. For a zero-order reaction, the rate of reaction is:
A) Directly proportional to the concentration of the reactant.
B) Inversely proportional to the concentration of the reactant.
C) Independent of the concentration of the reactant.
D) Proportional to the square of the concentration of the reactant.
48. Which of the following factors does NOT typically affect the rate of a chemical reaction?
A) Concentration of reactants
B) Temperature
C) Physical state of reactants
D) Color of the reactants
49. What is the instantaneous rate of reaction at time 't' for a reaction A -> Products?
A) -d[A]/dt
B) d[A]/dt
C) [A]/dt
D) -dt/[A]
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