NCERT Class XII Chemistry
Chapter - Surface Chemistry
Questions with Solutions

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Question : 2
Total: 35
What is the difference between physisorption and chemisorption?
Solution:  
 Physisorption  Chemisorption
 The adsorbate and adsorbentare held by weak van der Waalsforces.  The adsorbate and adsorbent areheld by forces similar to a chemicalbond.
 Heat of adsorption is of theorder of 20 kJ/mol.  Heat of adsorption is of the order of200 kJ/mol.
 It is reversible.  It is irreversible.
 It decreases with increase intemperature and occurs at lowertemperatures.  It increases with temperature andoccurs at high temperature.
 It is not specific in nature, i.e., allgases are adsorbed on all solidsto some extent.  It is specific in nature and occursonly when a chemical bond isformed between the adsorbate andadsorbent.
 Multimolecular layers may beformed on the adsorbent.  Usually unimolecular layer is formedon the adsorbent.
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