<<–2/”>a href=”https://exam.pscnotes.com/5653-2/”>p>chemisorption and physisorption.
Introduction
Adsorption is a surface phenomenon where Molecules (adsorbate) adhere to the surface of a solid or liquid (adsorbent). This process plays a crucial role in various industrial and natural processes, ranging from catalysis to water purification. Chemisorption and physisorption are two distinct types of adsorption, differing in the nature of the forces involved and their overall characteristics.
Key Differences: Chemisorption vs. Physisorption
| Characteristic | Chemisorption | Physisorption |
|---|---|---|
| Forces Involved | Chemical Bonds (covalent, ionic) are formed between adsorbate and adsorbent. | Weak van der Waals forces of attraction exist between adsorbate and adsorbent. |
| Specificity | Highly specific â occurs only if chemical bonds can form. | Non-specific â can occur between most gases and solids under appropriate conditions. |
| Heat of Adsorption | High (40-400 kJ/mol) due to chemical bond formation. | Low (20-40 kJ/mol) similar to the heat of condensation. |
| Reversibility | Irreversible, or reversible with difficulty, as breaking chemical bonds requires energy. | Reversible â easily removed by decreasing pressure or increasing temperature. |
| Temperature Dependence | Occurs at higher temperatures, as activation energy is needed for bond formation. | Occurs at lower temperatures, as weak forces are disrupted at higher temperatures. |
| Adsorption Layers | Usually forms a monolayer. | Can form multilayers. |
| Examples | Adsorption of hydrogen on Metal surfaces (used in hydrogenation reactions). | Adsorption of nitrogen on charcoal (used in gas masks). |
Advantages and Disadvantages of Chemisorption and Physisorption
| Adsorption Type | Advantages | Disadvantages |
|---|---|---|
| Chemisorption | High adsorption capacity, specific, strong bonding, potential for catalysis, stability. | Requires higher activation energy, irreversible in some cases, limited to specific adsorbents. |
| Physisorption | Low activation energy, reversible, broad applicability, useful for separation processes. | Low adsorption capacity, non-specific, weak bonding, sensitive to temperature and pressure changes. |
Similarities Between Chemisorption and Physisorption
- Both are surface phenomena.
- Both increase with increasing surface area of the adsorbent.
- Both decrease with increasing temperature (though the effect is more pronounced in physisorption).
- Both can be used in various industrial applications.
FAQs on Chemisorption and Physisorption
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Is chemisorption always irreversible? While most chemisorption processes are irreversible, some can be reversed with difficulty under specific conditions (e.g., high temperature).
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Which type of adsorption is better? There’s no universally “better” type. The choice depends on the specific application and the desired characteristics.
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What factors affect adsorption? Temperature, pressure, surface area of the adsorbent, nature of the adsorbate and adsorbent, and the presence of other molecules on the surface.
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Why is physisorption favored at low temperatures? At low temperatures, the kinetic energy of gas molecules decreases, making it easier for the weak van der Waals forces to hold them to the surface.
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What are some applications of adsorption? Catalysis, gas masks, water purification, air purification, chromatography, drying agents, and pharmaceutical drug delivery.
Let me know if you have any other questions!