61. What is the effect of temperature on the adsorption of gases on solids?
- a) Adsorption increases with an increase in temperature.
- b) Adsorption decreases with an increase in temperature.
- c) Adsorption remains constant with an increase in temperature.
- d) Adsorption first increases and then decreases with an increase in temperature.
Answer: b) Adsorption decreases with an increase in temperature
Explanation: Adsorption is an exothermic process, so according to Le Chatelier’s principle, increasing the temperature shifts the equilibrium towards desorption, reducing the extent of adsorption.
62. Which of the following isotherms is associated with multilayer adsorption?
- a) Langmuir isotherm
- b) Freundlich isotherm
- c) BET isotherm
- d) Temkin isotherm
Answer: c) BET isotherm
Explanation: The BET isotherm explains the adsorption of gases on solids and can account for the formation of multilayers of adsorbate molecules.
63. Which of the following characteristics is incorrect for physical adsorption?
- a) It is reversible.
- b) It forms a multilayer of adsorbate.
- c) It occurs at high temperatures.
- d) It involves weak Van der Waals forces.
Answer: c) It occurs at high temperatures
Explanation: Physical adsorption generally occurs at low temperatures because the weak Van der Waals forces holding the adsorbate to the surface are not strong enough to overcome increased thermal energy at high temperatures.
64. Which of the following is true for both physisorption and chemisorption?
- a) Both are endothermic processes.
- b) Both involve Van der Waals forces.
- c) Both increase with decreasing temperature.
- d) Both involve the attraction of molecules to a solid surface.
Answer: d) Both involve the attraction of molecules to a solid surface
Explanation: Both physisorption and chemisorption involve the attraction of adsorbate molecules to the surface of a solid, though the nature of the forces differs (weak Van der Waals forces in physisorption and stronger chemical bonds in chemisorption).
65. In which of the following is the interaction between adsorbent and adsorbate the strongest?
- a) Physisorption of CO₂ on charcoal
- b) Chemisorption of H₂ on nickel
- c) Physisorption of N₂ on silica gel
- d) Adsorption of water on silica gel
Answer: b) Chemisorption of H₂ on nickel
Explanation: Chemisorption involves strong chemical bonds between the adsorbent and the adsorbate, making the interaction stronger than in physisorption, which only involves weak Van der Waals forces.
66. Which of the following adsorption processes involves an increase in entropy?
- a) Chemisorption
- b) Physisorption
- c) Adsorption of gases on a solid
- d) Adsorption of solutes from solution
Answer: d) Adsorption of solutes from solution
Explanation: When a solute is adsorbed from a solution onto a solid surface, the solvent molecules are freed from the solvation shell of the solute, leading to an increase in the entropy of the system.
67. Which of the following factors does not affect the adsorption of gases on solids?
- a) Temperature
- b) Pressure
- c) Nature of adsorbent
- d) Volume of the gas
Answer: d) Volume of the gas
Explanation: The extent of adsorption depends on the temperature, pressure, and nature of the adsorbent, but not directly on the volume of the gas.
68. Which type of adsorption is likely to occur when a gas is adsorbed on a non-reactive solid surface like charcoal at low temperature?
- a) Chemisorption
- b) Physisorption
- c) Both physisorption and chemisorption
- d) Neither physisorption nor chemisorption
Answer: b) Physisorption
Explanation: Physisorption occurs at low temperatures and involves weak Van der Waals forces, making it the likely type of adsorption when a gas is adsorbed on a non-reactive surface like charcoal.
69. Which one of the following does NOT apply to the adsorption process?
- a) It is spontaneous.
- b) It increases with increasing surface area.
- c) It increases with increasing temperature.
- d) It is exothermic.
Answer: c) It increases with increasing temperature
Explanation: Adsorption is generally exothermic and decreases with increasing temperature because high thermal energy discourages the adherence of adsorbate molecules to the surface.
70. The Langmuir adsorption isotherm is based on the assumption that:
- a) Adsorption occurs on a heterogeneous surface.
- b) Adsorption forms a multilayer of adsorbate.
- c) Adsorption occurs on specific homogeneous sites on the surface.
- d) Adsorption occurs at variable energies at different sites.
Answer: c) Adsorption occurs on specific homogeneous sites on the surface
Explanation: The Langmuir adsorption isotherm assumes a homogeneous surface with specific sites for adsorption, where only a monolayer is formed.
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