BET Isotherm

Question 1

What are the six assumption of BET model?

Answer 1

BET model, six assumptions
• Adsorbent has equal energy adsorption sites
• Adsorption localised to these sites
• Neighbouring adsorbed molecules do not interact
• Multilayer formation unlimited
• Enthalpy of adsorption in second and subsequent multilayers equal to enthalpy of liquefaction
• Adsorption/desorption may only occur on or from exposed sites

Question 2

Difference between Langmuir and BET isotherm

Answer 2

• BET fails to predict experimental results at high pressures
=> Langmuir ignores possibility of adsorbate acting as surface itself

Question 3

Describe the graphs of mesoporous, real ‘nonporous’ solid and microporous solid

Answer 3

• Mesoporous solid - straight line
• Real ‘non porous’ solid - upturn curve
• Microporous solid - steep upturn curve