Problem 85 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statement is wrong about chemisorption? (1) it is reversible in nature (2) it is specific in nature (3) it first increases with increase in temperature and then pressure (4) it involves the formation of a compound on the surface of the solid adsorbent (a) 1 only (b) 2 and 3 (c) 1 and 3 (d) 2 and 4

Step-by-Step Solution

Answer

Option (c) 1 and 3 are the incorrect statements about chemisorption.

Step 1: Understand Chemisorption

Chemisorption is a type of adsorption where a chemical bond forms between the adsorbate and the surface of the adsorbent. It involves interactions at a molecular level, forming compounds or bonds on the surface.

Step 2: Evaluate Statement 1

Statement 1 claims that chemisorption is reversible in nature. Chemisorption typically forms strong covalent bonds, making it generally irreversible, unlike physisorption. Hence, Statement 1 is incorrect.

Step 3: Evaluate Statement 2

Statement 2 states that chemisorption is specific in nature. Chemisorption is indeed specific as it involves the formation of chemical bonds, which depend on the nature of the adsorbate and adsorbent materials. Thus, Statement 2 is correct.

Step 4: Evaluate Statement 3

Statement 3 claims that chemisorption first increases with an increase in temperature and then with pressure. Chemisorption requires an initial activation energy, often increasing with temperature until optimal, but the role of pressure isn't directly stated to change or be essential abundantly. This assertion is partially correct.

Step 5: Evaluate Statement 4

Statement 4 indicates that chemisorption involves the formation of a compound on the surface of the solid adsorbent. This is true, as chemisorption involves chemical bonding that forms compounds at the surfaces. Therefore, Statement 4 is correct.

Step 6: Determine Incorrect Statements

Based on the above evaluations, Statements 1 and part of Statement 3 are incorrect. While chemisorption may have temperature-dependent variances, its irreversibility (as opposed to what Statement 1 claims) primarily makes it wrongfully represented in Statement 3.

Step 7: Final Answer Choice

Given the analysis, the incorrect statements are primarily found in Statements 1 and 3. Hence, the right answer choice is option (c) 1 and 3.

Key Concepts

Adsorption Processes

Adsorption is the process where molecules, atoms, or ions are attracted and held onto a surface. This process can occur in various forms, with chemisorption being one of the more significant types due to its strong and specific interactions.

• Adsorption occurs when the adsorbate (the substance being absorbed) adheres to the surface of the adsorbent (the material doing the absorbing).
• There are two primary types of adsorption processes: physisorption and chemisorption.
• Physisorption involves weak Van der Waals forces and is generally reversible.
• Chemisorption involves the formation of strong chemical bonds and is usually irreversible.

In chemisorption, the process often requires an activation energy to initiate the bond formation. This means that the adsorption efficiency can vary with temperature, often increasing as temperature rises due to the activation energy overcoming barriers. Understanding the differences between physisorption and chemisorption is crucial for applications in catalysis, sensor technology, and separations.

Chemical Bonding

Chemisorption is directly related to chemical bonding because it involves the formation of chemical bonds between the adsorbate and the surface of the adsorbent. This bonding specificity sets chemisorption apart from physisorption.

• In chemisorption, the nature of the bonds formed can be covalent or ionic, depending on the materials involved.
• The process typically involves electron transfer or sharing, which can lead to the formation of new compounds at the surface.
• The specificity of these chemical bonds means that chemisorption is selective, only occurring when the right conditions for bond formation are present.

Because chemisorption creates a strong bond, it also often leads to a change in the electronic state of the adsorbate, sometimes affecting the chemical properties of the adsorbed species. This change is a reason why chemisorption is widely studied in catalysis and surface science.

Irreversibility in Chemistry

Irreversibility is a key feature in chemisorption and differentiates it from physisorption. Once a chemical bond is formed through chemisorption, it is difficult to reverse.

• The strong chemical bonds involved make it energetically unfavorable to simply reverse the process without altering conditions drastically.
• Irreversibility means that, under normal conditions, the adsorbate will not easily leave the surface once it is bonded.
• In practical terms, this can be advantageous for processes like catalytic converter functioning and metal coating.

Understanding irreversibility in chemisorption is important for applications where long-term stability and durability of the adsorbents are required. This concept is integral in industrial applications, where the efficiency and effective lifespan of catalysts are critical considerations.