| Property | Physisorption | Chemisorption |
|---|---|---|
| Forces involved | Van der Waals (weak) | Chemical bonds (strong) |
| Enthalpy | 20–40 kJ/mol (low) | 80–240 kJ/mol (high) |
| Specificity | Non-specific (any adsorbate on any adsorbent) | Highly specific (particular pairs) |
| Reversibility | Reversible (easily) | Irreversible |
| Number of layers | Multilayer possible | Monolayer only |
| Activation energy | Low or nil | Appreciable |
| Temperature effect | Decreases with T (Le Chatelier) | First increases (overcome Ea), then decreases |
| Example | on charcoal at low T | on Ni surface |
Memory Aid: "Physi is WEAK and MULTI, Chemi is STRONG and MONO"
- Physisorption: Weak van der Waals, Multilayer, Reversible, Decreases with T
- Chemisorption: Strong chemical bonds, Monolayer, Irreversible, First increases then decreases with T
Critical Distinction for NEET: The temperature behavior is the most frequently tested difference. Do NOT confuse: physisorption ALWAYS decreases with T; chemisorption shows a MAXIMUM then decreases.