CHEM 433 – 11/1/11

V. Phase Equilibria (Pure Substances)

• Intro & definitions.

• Phase diagrams

- CO2 , H2O, 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(Tb): 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 (Tf): T at which liquid and solid are in EQ at a given p.

Normal/Standard Tf: 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 :CO2

1)How much pressure is needed to liquefy CO2?

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 :H2O

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 = 109 Pa = 104 bar)http://www.youtube.com/watch?v=O42K4EwVssQ

Phase diagram of H2O 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