11. Which of the following is true for the adsorption of gases on a solid surface?
- a) The extent of adsorption increases at high temperature.
- b) The extent of adsorption decreases with an increase in surface area of the adsorbent.
- c) The extent of adsorption increases with a decrease in temperature.
- d) Adsorption occurs more easily on smooth surfaces.
Answer: c) The extent of adsorption increases with a decrease in temperature.
Explanation: Adsorption is an exothermic process, and according to Le Chatelier’s principle, lowering the temperature favors adsorption by shifting the equilibrium towards more adsorption.
12. Which of the following factors does NOT affect the rate of physisorption?
- a) Nature of adsorbent
- b) Temperature
- c) Pressure
- d) Bonding between adsorbate and adsorbent
Answer: d) Bonding between adsorbate and adsorbent
Explanation: Physisorption involves weak Van der Waals forces and does not require any bonding between the adsorbate and adsorbent. Chemisorption, on the other hand, involves chemical bonding.
13. Which of the following statements is true about adsorption?
- a) It is always irreversible.
- b) It involves the formation of a multilayer of molecules.
- c) It results in the increase of entropy of the system.
- d) It is spontaneous and results in a decrease of free energy.
Answer: d) It is spontaneous and results in a decrease of free energy.
Explanation: Adsorption is spontaneous, leading to a decrease in the system’s free energy (ΔG < 0), though the process reduces the entropy (ΔS < 0) since it involves the ordering of adsorbate molecules on the surface of the adsorbent.
14. The Langmuir adsorption isotherm assumes that:
- a) Adsorption is a reversible process.
- b) The surface is homogeneous.
- c) Multilayer adsorption occurs.
- d) There is a fixed number of adsorption sites.
Answer: b) The surface is homogeneous.
Explanation: The Langmuir adsorption isotherm assumes that the surface of the adsorbent is uniform (homogeneous) and that all adsorption sites are equivalent.
15. Freundlich adsorption isotherm applies to:
- a) Ideal gases
- b) Ideal liquids
- c) Both monolayer and multilayer adsorption
- d) Only monolayer adsorption
Answer: c) Both monolayer and multilayer adsorption
Explanation: Freundlich adsorption isotherm is empirical and can describe both monolayer and multilayer adsorption, depending on the adsorbent-adsorbate interaction.
16. At low pressure, adsorption of a gas on a solid follows which order?
- a) First order
- b) Zero order
- c) Second order
- d) Third order
Answer: a) First order
Explanation: At low pressures, the amount of gas adsorbed varies directly with the pressure, so adsorption follows first-order kinetics.
17. Which of the following is a characteristic of physisorption?
- a) It occurs at high temperatures.
- b) It requires a large amount of activation energy.
- c) It forms multiple layers of adsorbate on the surface.
- d) It is highly specific.
Answer: c) It forms multiple layers of adsorbate on the surface.
Explanation: Physisorption can lead to multilayer adsorption because the forces involved (Van der Waals forces) allow for weak attraction of more than one layer of molecules onto the surface of the adsorbent.
18. Chemisorption typically:
- a) Involves weak Van der Waals forces.
- b) Occurs at low temperatures.
- c) Forms multilayers of adsorbate.
- d) Requires activation energy.
Answer: d) Requires activation energy.
Explanation: Chemisorption involves the formation of strong chemical bonds between adsorbate and adsorbent, which requires activation energy, unlike physisorption.
19. The BET isotherm is primarily used to describe:
- a) Monolayer adsorption
- b) Multilayer adsorption
- c) Chemical adsorption
- d) Gaseous adsorption on metals
Answer: b) Multilayer adsorption
Explanation: The BET (Brunauer, Emmett, Teller) isotherm is an extension of the Langmuir model and describes multilayer adsorption, where the adsorbate forms multiple layers on the adsorbent surface.
20. Which of the following is NOT a correct assumption of the Langmuir adsorption isotherm?
- a) Adsorption sites are equivalent.
- b) Adsorption occurs uniformly over the surface.
- c) Multilayer adsorption occurs.
- d) Adsorption is restricted to a monolayer.
Answer: c) Multilayer adsorption occurs.
Explanation: Langmuir adsorption isotherm assumes adsorption occurs only in a single monolayer, not multilayer adsorption.
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