31. In the context of adsorption, the term “sorption” refers to:
- a) Only adsorption
- b) Only absorption
- c) Both adsorption and absorption
- d) Neither adsorption nor absorption
Answer: c) Both adsorption and absorption
Explanation: Sorption is a general term that refers to both adsorption (surface phenomenon) and absorption (bulk phenomenon).
32. Which statement is true for chemisorption as compared to physisorption?
- a) Chemisorption is non-specific.
- b) Chemisorption is reversible.
- c) Chemisorption requires activation energy.
- d) Chemisorption involves weak forces.
Answer: c) Chemisorption requires activation energy.
Explanation: Chemisorption involves the formation of chemical bonds, which typically require activation energy. This makes it different from physisorption, which involves weak Van der Waals forces and occurs at lower temperatures without significant energy input.
33. A decrease in temperature usually:
- a) Increases physisorption and decreases chemisorption.
- b) Increases chemisorption and decreases physisorption.
- c) Increases both physisorption and chemisorption.
- d) Decreases both physisorption and chemisorption.
Answer: a) Increases physisorption and decreases chemisorption.
Explanation: Physisorption increases at lower temperatures because it involves weak Van der Waals forces that are enhanced at lower kinetic energies. Chemisorption, on the other hand, often requires higher temperatures for bond formation and activation energy.
34. Activated charcoal is used to adsorb gases because:
- a) It is inexpensive
- b) It has a high surface area
- c) It is chemically reactive
- d) It is inert
Answer: b) It has a high surface area
Explanation: Activated charcoal has an extremely high surface area, allowing it to adsorb large amounts of gases and impurities, making it ideal for use in air purification and gas masks.
35. Adsorption of gases on solids can be increased by:
- a) Increasing temperature
- b) Increasing surface area of the solid
- c) Decreasing pressure
- d) Using smooth surfaces
Answer: b) Increasing surface area of the solid
Explanation: The greater the surface area of the adsorbent, the more sites are available for adsorption, hence increasing the extent of adsorption.
36. Which of the following is NOT true for physisorption?
- a) It forms a multilayer of adsorbate.
- b) It occurs at low temperatures.
- c) It is highly specific.
- d) It is reversible.
Answer: c) It is highly specific.
Explanation: Physisorption is not specific to any particular type of adsorbate and occurs through weak Van der Waals forces, making it a non-specific process.
37. Which of the following adsorption isotherms explains the formation of a monolayer of adsorbate?
- a) Langmuir isotherm
- b) Freundlich isotherm
- c) BET isotherm
- d) Temkin isotherm
Answer: a) Langmuir isotherm
Explanation: The Langmuir adsorption isotherm assumes the formation of a monolayer on the adsorbent surface and that all adsorption sites are equivalent.
38. For physical adsorption, the enthalpy change (ΔH) is generally:
- a) Highly positive
- b) Highly negative
- c) Slightly negative
- d) Zero
Answer: c) Slightly negative
Explanation: Physical adsorption (physisorption) releases a small amount of heat, making the enthalpy change slightly negative. The process is exothermic, but the energy released is not as large as in chemisorption.
39. The extent of adsorption of a gas on a solid is generally:
- a) Inversely proportional to pressure at constant temperature.
- b) Directly proportional to pressure at constant temperature.
- c) Independent of temperature.
- d) Independent of pressure.
Answer: b) Directly proportional to pressure at constant temperature.
Explanation: As pressure increases at constant temperature, more gas molecules collide with the solid surface, increasing the extent of adsorption. This is particularly true at low pressures.
40. Which of the following statements is correct for adsorption?
- a) Adsorption increases with an increase in temperature.
- b) Adsorption is an endothermic process.
- c) Adsorption increases with an increase in surface area.
- d) Adsorption is independent of the adsorbate.
Answer: c) Adsorption increases with an increase in surface area.
Explanation: A larger surface area provides more adsorption sites, leading to greater adsorption of gases or solutes.
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