Q.Distinguish between the following:
Physisorption and chemisorption. Give one example.

Step 1. Nature of forces. Physisorption involves only weak van der Waals forces between adsorbate and adsorbent; chemisorption involves a genuine chemical bond, covalent or ionic.

Step 2. Specificity and heat. Physisorption is not specific (any gas physisorbs on any solid to some extent) and releases a relatively low heat of adsorption (20-40 kJ/mol); chemisorption is highly specific (only where a bond can form) and releases a higher heat of adsorption (40-200 kJ/mol).

Step 3. Temperature behaviour and reversibility. Physisorption occurs at low temperature and decreases as temperature rises; it is readily reversible by lowering pressure or raising temperature. Chemisorption is favoured at higher temperature (up to a point, after which it too falls off as bonds break); it is essentially irreversible. …

Point-by-point contrast drawn from Table 11.2, using the same N2-on-iron example …

• Reversing the heat-of-adsorption ranges (physisorption is the LOW range, chemisorption the HIGH range).
• Using two unrelated examples for the two types instead of the textbook's own paired example (N2 on iron at low vs high te …