CHAPTER 5 Flashcards
What makes the liquid a condensed phase is____
the strong intermolecular cohesion (attractive force)
Do systems have a natural tendency to reduce or increase their interfacial areas?
reduce (which is why drops are spherical…min sa)
When is the pressure difference 0 in the laplace-young equation?
when the interface remains planar
What is homogeneous nucleation?
nucleation due to collision of gas molecules
What is heterogeneous nucleation?
nucleation involving the adsorption of gas molecules onto a pre-existing surface; these adsorbed gas molecules form clusters on the surface that grow until they are large enough to condense ou tof liquid nuclei
When does nucleation occur in terms of vapor pressure of sphere and external pressure?
When P*vap (sphere) > P ext
What is the difference between adsorption and absoption
Adsorption: restricted to surface of fluid (interfacial region)
Absorption: species transferred into bulk of adsorptions
What are the assumptions of langmuir model?
1) adsoption is restricted to single monolayer
2) all sites on adsorbent are energetically identical
3) gas is ideal
What does θ in the langmuir model represent?
fraction of occupied sites
What are the assumptions for the BET model?
1) adsorption can extend into multilayers
2) all sites within a given layer are energetically identical
3) energetics of adsorption in the 1st layer is diff from that in the other layers
4) adsorption in layers 2,3,4,… is very similar to what occurs during condensation of gas molecules
5) gas is ideal
What is θ_0 and θ_n in the BET model?
θ_0 : fraction of sites covered by zero molecules
θ_n : fraciton of sites covered by n molecules
What is the K in the BET model?
equilibrium constant for condensation of pure
