Adsorption Flashcards
What are the two types of adsorption?
Physisorption, Chemisorption
Give the factors which adsorbate quantity depends on
Adsorbate quantity depends on :
adsorbate type, adsorbent type, adsorbate concentration, adsorbent SA, temperature
Define desorption
Reverse of adsorption => species evolved or removed from surface and concentration reduced
Define Physisorption
Weak V.D.W forces
Define chemisorption
Chemical bonds formed during process => only occurs if system able to form bonds
Properties of physisorption
Properties:
low heat of adsorption,
fast rate of adsorption, uptake decreases with increasing temp,
easy desorption, adsorbate unchanged when desorbed,
non specific,
mono or multilayer coverage
Why is physisorption always exothermic?
Always exothermic due to increased adsorbate order
Properties of chemisorption
Properties:
high heat of adsorption,
slow rate of adsorption,
uptake increases as temp increases, difficult desorption, different desorption to original adsorptive, very specific, monolayer coverage
Why is chemisorption endothermic?
Electron transfer between adsorbate and adsorbent –> chemical bonds formed
