CHEM 433 – 11/1/11

V. Phase Equilibria (Pure Substances) • Intro & definitions.

• Phase diagrams - CO

2 ,

H

2

O, C • Phase Stability vs. T

READ: CHAPTER 4 HW #6: via e-mail – DUE Th.

EXAM #3 on Tuesday – review(s) Monday Web up to date with review sheet today.

Phase: A form of mater, uniform in chemical composition and physical state.

Phase Transition: The spontaneous conversion of one phase to another (e.g. g —> l) Transition Temperature (Ttrs): Chemical potentials of 2 phases are equal and the 2 phases are in equilibrium Phase Diagram: Shows regions of P and T in which phases are stable Phase boundaries: p and T where 2 phases co-exist (in eq. ,  ’s are =).

Vapor pressure: pressure of vapor in eq. with liquid (the l-v boundary).

Sublimation vapor pressure: pressure of vapor in eq. with solid (s-v phase boundary)

Boiling: A condition of free vaporization throughout the liquid.

Boiling temperature(T b ): T at which vapor pressure equals external pressure Normal boiling: boiling T at 1 atm external pressure Standard boiling point: boiling T at 1 bar external pressure.

Freezing/Melting Temperature (T f ): T at which liquid and solid are in EQ at a given p.

Normal/Standard T f : as above, for 1 atm or 1 bar, respectively.

Triple point: Temperature and pressure at which 3 phases coexist (usually s, l, g).

Critical temperature: T when surface between phases disappears (closed system). Density of (l) and (g) become equal!

Critical pressure: vapor pressure at critical temperature.

Supercritical Fluid: The name of the phase above the critical point.

Phase Diagram :CO 2 1)How much pressure is needed to liquefy CO 2 ?

2)What is its

normal boiling point

?

3) What is T of “dry ice bath”?

4)What phase does one have at T = 310K?

5)Is slope (dP/dT) of solid liquid boundary “+” or “–”?

Phase Diagram :H 2 O 1) Notice slope of “Ice I” – liquid boundary – positive or negative?

2)How many triple points 3)What is Tc (presumably)?

Phase diagram for Carbon (note 1 GPa = 10 9 Pa = 10 4 bar) http://www.youtube.com/watch?v=O42K4EwVssQ

Phase diagram of H 2 O and the greenhouse effect

This picture is a “slice” through the phase diagram at p > T.P.

You re-draw this for: 1) p < that of triple point 2) p = to that of triple point