81. Which of the following is not a characteristic of chemisorption?
- a) It is highly specific.
- b) It is usually irreversible.
- c) It forms multilayers of adsorbate.
- d) It involves chemical bonds.
Answer: c) It forms multilayers of adsorbate
Explanation: Chemisorption forms a monolayer of adsorbate, as it involves strong chemical bonding with specific sites on the adsorbent surface. Multilayer formation is characteristic of physisorption.
82. Which of the following changes occur during adsorption?
- a) Enthalpy increases and entropy decreases.
- b) Enthalpy decreases and entropy decreases.
- c) Enthalpy increases and entropy increases.
- d) Enthalpy decreases and entropy increases.
Answer: b) Enthalpy decreases and entropy decreases
Explanation: Adsorption is an exothermic process (enthalpy decreases), and as the molecules become more ordered on the surface, the randomness or disorder of the system decreases (entropy decreases).
83. In physisorption, adsorption decreases with:
- a) Increase in temperature
- b) Increase in pressure
- c) Decrease in temperature
- d) Decrease in surface area
Answer: a) Increase in temperature
Explanation: Physisorption is favored at low temperatures because it involves weak Van der Waals forces. As temperature increases, the thermal energy of the adsorbate molecules increases, leading to desorption.
84. What is the main difference between chemisorption and physisorption?
- a) Chemisorption is non-specific, and physisorption is specific.
- b) Chemisorption requires activation energy, while physisorption does not.
- c) Chemisorption is reversible, while physisorption is irreversible.
- d) Chemisorption forms multilayers, while physisorption forms a monolayer.
Answer: b) Chemisorption requires activation energy, while physisorption does not
Explanation: Chemisorption involves the formation of chemical bonds, which often requires activation energy, whereas physisorption is governed by weak Van der Waals forces and does not require significant activation energy.
85. In which of the following adsorption processes is the enthalpy change the highest?
- a) Physisorption of CO₂ on activated charcoal
- b) Chemisorption of hydrogen on nickel
- c) Adsorption of nitrogen on silica gel
- d) Adsorption of water vapor on silica gel
Answer: b) Chemisorption of hydrogen on nickel
Explanation: Chemisorption involves the formation of strong chemical bonds, leading to a higher enthalpy change compared to the weak interactions involved in physisorption.
86. Freundlich adsorption isotherm fails at:
- a) Low pressure
- b) High pressure
- c) Low temperature
- d) High temperature
Answer: b) High pressure
Explanation: The Freundlich adsorption isotherm fails at high pressure because it does not account for the saturation of the adsorbent, where no more adsorption can occur regardless of further increases in pressure.
87. At low temperatures, the adsorption of gas on solid is mainly:
- a) Chemisorption
- b) Physisorption
- c) Both physisorption and chemisorption
- d) Desorption
Answer: b) Physisorption
Explanation: Physisorption predominates at low temperatures because it involves weak Van der Waals forces. Chemisorption requires higher temperatures due to its need for activation energy.
88. Which of the following statements is incorrect regarding adsorption?
- a) Adsorption is a surface phenomenon.
- b) Adsorption is an endothermic process.
- c) Adsorption increases with an increase in surface area.
- d) Adsorption decreases with an increase in temperature.
Answer: b) Adsorption is an endothermic process
Explanation: Adsorption is an exothermic process, where heat is released when the adsorbate molecules adhere to the surface of the adsorbent.
89. What is the main assumption of the Langmuir adsorption isotherm?
- a) The surface is heterogeneous.
- b) Adsorption can occur at variable energies.
- c) All adsorption sites are equivalent.
- d) Multilayer adsorption occurs.
Answer: c) All adsorption sites are equivalent
Explanation: The Langmuir adsorption isotherm assumes that the adsorbent surface is homogeneous, with all adsorption sites being equivalent and able to hold only one molecule of adsorbate.
90. The efficiency of an adsorbent increases with:
- a) Decrease in surface area
- b) Decrease in particle size
- c) Increase in temperature
- d) Increase in pressure
Answer: b) Decrease in particle size
Explanation: Decreasing the particle size increases the surface area available for adsorption, making the adsorbent more efficient.
Leave a comment