Answer the questions based on the passage given below:

Adsorption is a surface phenomenon and it differs from absorption which occurs throughout the body of the substance that absorbs. In physisorption the attractive forces are mainly van der Waals forces while in chemisorption ionic / covalent bonds are formed between particles of adsorbent and adsorbate. The catalytic activity of finely divided iron in Haber's process of ammonia manufacture can be explained by adsorption theory. Adsorption being an exothermic process, the heat of adsorption is utilized in enhancing the rate of the reaction. Adsorption has many applications being used in gas masks, control of humidity, chromatograph separation, curing diseases etc.

Which of the following is not correct regarding the adsorption of a gas on the surface of solid?

A. On increasing temperature, adsorption increasescontinuously

B. Enthalpy and entropy changes are negative

C. Chemical adsorption is more specific than physical adsorption

D. High temperature favours physical adsorption.

Choose the correct answers from the options given below:

A and D only

The correct answer is option 1. A and D only.

Let us explain each statement in detail regarding the adsorption of gases on solid surfaces:

Statement A: On increasing temperature, adsorption increases continuously

Adsorption involves the adhesion of gas molecules onto the surface of a solid. This process is typically exothermic, meaning it releases heat.

Effect of Temperature: According to Le Chatelier's principle, for an exothermic process, increasing the temperature shifts the equilibrium towards the reactants (in this case, desorption rather than adsorption). Thus, as temperature increases, the amount of gas adsorbed onto the surface usually decreases because the higher temperature provides energy that disrupts the adsorbed molecules.

Conclusion: Adsorption does not increase continuously with temperature; rather, it generally decreases with increasing temperature. Thus, statement A is incorrect.

Statement B: Enthalpy and entropy changes are negative

Enthalpy Change (\(\Delta H\)): Adsorption is an exothermic process, meaning it releases heat. As a result, the enthalpy change for adsorption is negative (\(\Delta H < 0\)).

Entropy Change (\(\Delta S\)): When a gas adsorbs onto a solid surface, the molecules become more ordered compared to their state in the gas phase. This reduction in disorder (entropy) means that the entropy change is negative (\(\Delta S < 0\)).

Conclusion: Both enthalpy and entropy changes are typically negative during adsorption, making statement B correct.

Statement C: Chemical adsorption is more specific than physical adsorption

Chemical Adsorption (Chemisorption): Involves the formation of chemical bonds between the adsorbate and the adsorbent. This process is highly specific because it depends on the chemical nature of both the adsorbate and the surface.

Physical Adsorption (Physisorption): Involves weaker van der Waals forces and is generally less specific because it does not rely on specific chemical interactions.

Conclusion: Chemical adsorption is indeed more specific than physical adsorption. Therefore, statement C is correct.

Statement D: High temperature favors physical adsorption

Physical Adsorption: This process is exothermic and is favored at lower temperatures. Increasing the temperature generally leads to a decrease in the extent of physical adsorption because the additional thermal energy disrupts the weak van der Waals forces holding the gas molecules on the surface.

Conclusion: High temperature does not favor physical adsorption; rather, it tends to reduce the extent of physical adsorption.** Therefore, statement D is incorrect.

Summary:

Incorrect Statements: A and D are incorrect because:

A incorrectly states that adsorption increases with temperature.

D incorrectly suggests that high temperatures favor physical adsorption.

Correct Statements: B and C are correct because:

B accurately describes that both enthalpy and entropy changes are typically negative for adsorption.

C correctly notes that chemical adsorption is more specific than physical adsorption.

Thus, the correct choice is: 1. A and D only