1. Lecture 23: Review of Colligative Properties and Intro to Equilibrium
Colligative properties: freezing point depression solid  solution boiling point elevation solution  gas
Fractional distillation
Introduction to Chemical Equilibrium
vapor pressure

2. Freezing Point Depression
Solute must be excluded from solid
Consider equilibration of vapor pressure of solvent and solute.
liquid
solid
add solute
Vapor
Pressure
freezing point drops
Temperature

3. Boiling point increases
Boiling Point Elevation
Solute must be excluded from gas
There is a blanket of gas (an “atmosphere”) at a fixed pressure (typically 1 atm)
Boiling is when vapor pressure reaches blanket pressure.
liquid
add solute
Vapor
Pressure
blanket gas pressure
typically 1 atm
Boiling point increases
Temperature

4. slope
0.05 atm/K
Predict the boiling point of a solution of 8 mol of water and 1 mol of NaCl: NaCl(s)  Na+(aq) + Cl-(aq)
(1) 101°C (2) 102°C (3) 104°C (4) 108°C

5. Fractional Distillation
Solvent and solute are both volatile
Vapor is enriched in more volatile component
Can be quite complicated for non-ideal solutions
Step 1
X2soln = 0.75
X2vap = 0.66
Step 2
X2soln = 0.66
X2vap = 0.50 1 2
Step 3
X2soln = 0.50
X2vap = etc.