BET model for gas adsorption

Question 1

What’s the BET model formula?

Answer 1

~ P/(n(P-Po)) = 1/(NmC) + (C-1)/(NmC)*(P/Po)

~ C: constant

~ Nm: monolayer capacity (moles of adsorbed gas which form a complete monolayer)

~ n: moles of adsorbed gas at pressure p

Question 2

What happens if n is measured with increasing p?

Answer 2

~ a plot of P/(n(P-Po)) versus P/Po will yield a straight line

~ can solve for Nm

~ slope = C-1/(Nm*C)

~ intercept = 1/Nm*C

Question 3

What is σ?

Answer 3

~ area taken up by a single adsorbate molecule

Question 4

What is σNaNm = S?

Answer 4

~ area covered on a monolayer of all particle surfaces

Question 5

What is S’?

Answer 5

~ the specific surface area (per mass of sample)

~ [m^2/g]

Question 6

What do we get if the particles are assumed to be monosized spheres, and the mass m and density p are known?

Answer 6

~ r = 3/(p*S’)

Question 7

What does BET give us?

Answer 7

~ gives an indication of the extent of particle agglomeration affecting the other methods

Question 8

What is the volume of adsorbed gas measured by?

Answer 8

~ a measurement of differential pressure