Adsorption

Question 1

chemisorption

Answer 1

chemical adsorption, closer to surface, deeper well, covalent bonds

Question 2

physisorption

Answer 2

physical adsorption, further from surface, shallow well, non-covalent interactions

Question 3

types of adsorption behaviours

Answer 3

molecular adsorption, activated dissociative adsorption and non-activated dissociative adsorption

Question 4

direct measurement of sticking coefficients

Answer 4

King and Wells and LoS-SP

Question 5

langmiur kinetics for sticking coefficients

Answer 5

S decreases linearly with increasing coverage

Question 6

Kislink kinetics for sticking coefficients

Answer 6

precursor adsorption and S varies with coverage according to eqn

Question 7

indirect measurement of sticking coefficients

Answer 7

calibrated uptake measurements, plot surface conc against exposure

Question 8

adsorption isotherms

Answer 8

measurements of variation of equilibrium surface conc of adsorbate with gas pressure of adsorbate at fixed T

Question 9

coverage

Answer 9

describes how much adsorbate is on the surface

Question 10

measuring adsorption isotherms

Answer 10

volumetric, gravimetric using quartz crystal microbalance

Question 11

langmuir adsorption isotherm

Answer 11

saturation at high pressures as we reach filled monolayer

Question 12

Sigmoid isotherm

Answer 12

cooperative effects due to lateral interactions between adsorbed molecules

Question 13

Langmuir adsorption assumptions

Answer 13

surface is flat and uniform, adsorbate binds randomly, enthalpy of adsorption is the same for each site and independent of how much adsorbate is already present and adsorption can’t go beyond a monolayer

Question 14

BET isotherm

Answer 14

with physisorption at low temps can get multilayers

Question 15

Langmuir rate of desorption

Answer 15

first order, only depends on what’s on the surface