CHEM 433 – 11/5/10

V. Phase Equilibria (Pure Substances)

• Derivation of Phase Boundaries (4.6)

• Eherenfest Classification of Phase Transitions (4.7): 1st order vs. 2nd order

READ: FINISH CHAPTER 4

Thermodynamic Criterion of EQ:

“At equilibrium, the chemical potential of a substance is the same throughout the sample, regardless of how many phases are present.”

A typical Clausius-Claperon problem:

At sea level (Patm=760 Torr), H2O boils at 100°C. What is Tb in Boulder, CO (Patm= 620 Torr)?

a) 106 °C b) 100°C c) 96°C d) 72 °C

(Let’s look at the diagram and think first!)

Sample Exam #4 problem:

Starting from the Claperon Equation:

Show that the solid-vapour phase boundary is given by:

Where subH and subV refer to sublimation.

€

dp

dT=

Δ trsS

Δ trsV

€

p = p*e−χ where χ =ΔsubH

R

1

T−

1

T*

⎛

⎝ ⎜

⎞

⎠ ⎟

http://en.wikipedia.org/wiki/Glass_transition_temperature