Solution: (a) Differences between Physisorption and Chemisorption
Step 1 (Defining the Basis of Comparison): [1 Mark]
Physisorption (Physical Adsorption) arises due to weak van der Waals forces, whereas Chemisorption arises due to strong chemical bond formation.
Step 2 (Comparative Analysis): [1 Mark]
- Nature of Forces: Physisorption involves weak van der Waals forces; Chemisorption involves strong chemical bonds (covalent or ionic).
- Specificity: Physisorption is not specific in nature; Chemisorption is highly specific.
- Reversibility: Physisorption is reversible; Chemisorption is irreversible.
Step 3 (Thermodynamic and Kinetic Parameters): [1 Mark]
- Enthalpy of Adsorption: Physisorption has low enthalpy of adsorption ($20-40 \text{ kJ mol}^{-1}$); Chemisorption has high enthalpy of adsorption ($80-240 \text{ kJ mol}^{-1}$).
- Activation Energy: Physisorption requires very little or no activation energy; Chemisorption often requires high activation energy.
OR Solution: (b) Definitions with Examples
Step 1 (Lyophilic Sol): [1 Mark]
Definition: Lyophilic sols are "liquid-loving" colloidal systems where the dispersed phase has a strong affinity for the dispersion medium. They are stable and reversible.
Example: Starch, gum, or gelatin in water.
Step 2 (Macromolecular Colloid): [1 Mark]
Definition: These are substances having large molecular masses which, when dissolved in a suitable solvent, form a solution in which the size of the macromolecules is in the colloidal range.
Example: Naturally occurring polymers like proteins, cellulose, or synthetic polymers like polyethylene.
Step 3 (Coagulation): [1 Mark]
Definition: The process of settling down of colloidal particles as a precipitate by the addition of an excess of an electrolyte is known as coagulation or flocculation.
Example: Addition of alum to muddy water to remove suspended impurities.
💡 EL10 Concept Insight:
Think of Physisorption like a magnet sticking to a fridge (easy to pull off), while Chemisorption is like glue drying (it bonds permanently). Coagulation is simply like adding salt to a messy mixture to force all the floating bits to clump together and sink to the bottom so you can clear the water!