91. Which of the following best describes the adsorption of gases on a solid at high temperatures?
- a) Adsorption increases
- b) Adsorption decreases
- c) Adsorption is independent of temperature
- d) Adsorption increases at first and then decreases
Answer: b) Adsorption decreases
Explanation: Adsorption is an exothermic process, and increasing the temperature provides energy to the adsorbed molecules, causing them to desorb, thereby decreasing adsorption.
92. Which of the following is true for adsorption?
- a) Adsorption is spontaneous with a positive free energy change.
- b) Adsorption is non-spontaneous with a negative free energy change.
- c) Adsorption is spontaneous with a negative free energy change.
- d) Adsorption is non-spontaneous with a positive free energy change.
Answer: c) Adsorption is spontaneous with a negative free energy change
Explanation: Adsorption is spontaneous, meaning it occurs naturally, and the free energy change (ΔG) is negative. This is because the process results in a lower energy state.
93. Which of the following statements about chemisorption is incorrect?
- a) It is highly specific.
- b) It is reversible.
- c) It forms a monolayer.
- d) It involves the formation of chemical bonds.
Answer: b) It is reversible
Explanation: Chemisorption is typically irreversible due to the strong chemical bonds formed between the adsorbent and adsorbate.
94. In the adsorption of gases on solids, the plot of log x/mx/m versus log PP is a straight line with slope less than 1 in which isotherm?
- a) Langmuir isotherm
- b) BET isotherm
- c) Freundlich isotherm
- d) Temkin isotherm
Answer: c) Freundlich isotherm
Explanation: In the Freundlich adsorption isotherm, a plot of log x/mx/m (amount adsorbed per unit mass) versus log PP (pressure) gives a straight line with a slope less than 1, indicating the intensity of adsorption.
95. Which of the following is used to measure the surface area of an adsorbent?
- a) Freundlich adsorption isotherm
- b) BET adsorption isotherm
- c) Langmuir adsorption isotherm
- d) Van’t Hoff equation
Answer: b) BET adsorption isotherm
Explanation: The BET isotherm is widely used to determine the specific surface area of solids by analyzing gas adsorption data, especially in multilayer adsorption.
96. Adsorption of a gas on a solid is accompanied by a decrease in:
- a) Enthalpy only
- b) Entropy only
- c) Both enthalpy and entropy
- d) Neither enthalpy nor entropy
Answer: c) Both enthalpy and entropy
Explanation: Adsorption leads to a decrease in both enthalpy (because it is exothermic) and entropy (because the system becomes more ordered as molecules adhere to the solid surface).
97. Which of the following does not explain the mechanism of adsorption?
- a) Physical adsorption
- b) Chemisorption
- c) Le Chatelier’s principle
- d) Henry’s law
Answer: d) Henry’s law
Explanation: Henry’s law explains the solubility of gases in liquids, not the adsorption of gases on solid surfaces, which is better explained by physical adsorption, chemisorption, and Le Chatelier’s principle.
98. Which of the following is NOT involved in the adsorption process?
- a) Van der Waals forces
- b) Chemical bonds
- c) Covalent bonding
- d) Gravitational forces
Answer: d) Gravitational forces
Explanation: Gravitational forces are not involved in adsorption processes. Adsorption involves either weak Van der Waals forces (physisorption) or stronger chemical bonds (chemisorption).
99. In adsorption, when the rate of adsorption equals the rate of desorption, the system is said to be in:
- a) Chemical equilibrium
- b) Physical equilibrium
- c) Dynamic equilibrium
- d) Static equilibrium
Answer: c) Dynamic equilibrium
Explanation: In adsorption, when the rate of adsorption equals the rate of desorption, the system reaches dynamic equilibrium, where the amounts adsorbed and desorbed remain constant over time.
100. Which of the following correctly explains the relationship between temperature and chemisorption?
- a) Chemisorption increases with increasing temperature.
- b) Chemisorption decreases with increasing temperature.
- c) Chemisorption remains unaffected by temperature.
- d) Chemisorption first increases and then decreases with increasing temperature.
Answer: d) Chemisorption first increases and then decreases with increasing temperature
Explanation: Chemisorption requires activation energy, so it initially increases with temperature. However, at very high temperatures, desorption becomes significant, causing chemisorption to decrease.
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