Adsorption of gases onto solid surfaces

Question 1

What causes chemical adsorption?

Answer 1

~ large interaction forces and high heats of adsorption

Question 2

What are the characteristics of physical adsorption?

Answer 2

~ weak interaction forces (van der Waals)

~ more suitable for surface area analysis

Question 3

What’s the relationship between amount of physically adsorbed gas and temp?

Answer 3

~ physically adsorbed gas per unit surface area INCREASES with DECREASING temp

Question 4

How are surface area measurements generally made?

Answer 4

~ at cryogenic temps

~ isothermally increasing the gas pressure for pressures below the saturated vapor pressure Po (point at which the vapor condenses on itself)

Question 5

What is the type 1 isotherm?

Answer 5

~ highly porous

~ have a saturation point

~ pores fill with adsorbed gas and a saturation point is reached

Question 6

What is the type 2 isotherm?

Answer 6

~ non-porous particles, or particles with pores larger than micropores

~ monolayers are completed in succession