. BP = T where VP of a L is = atm P Triple pt. = s, l and g states - - PowerPoint PPT Presentation

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phase diagrams

Topic 7.5

• Strength of IMFs
• T

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Vapor pressure of liquid determined by:

Normal MP = melting T at 1 atm external P MP = T where VP of S = VP of L Normal BP = boiling T at 1 atm external P

Define MP in terms of VP: Define BP in terms of VP:

BP = T where VP of a L is = atm P

S G L

Temperature °C Pressure atm

Normal Sublimation pt. Triple pt. = s, l and g states have = VP, all are in EQ

.

Pure substance in closed system

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Phase Diagram

(a-b) liquid- gas curve- (a-c) sublim./deposition all T and P combinations where L + G in EQ (a-d) melting/freezing

Temperature °C Pressure atm

c

S + G

d

S + L

a b

L + G

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Critical Point

• Critical temperature

= T above which a G cannot be liquefied, regardless of P Critical T Critical P = T and P at which D

• f G and L are same

Super critical fluid Critical pt.

.

• Critical pressure

= P required to liquefy G at CT

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What happens to MP of CO2 as P↑? MP↑

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Phase diagram for water What happens to MP of H2O as P↑? MP↓

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• ↑ External P, particles compressed
• D ↑
• ↑ P favors more D phase
• S over L: so S has ↑ D

Slope of liquid/solid boundary line

• ↑ P, particles compressed
• D ↑
• H2O unusual in that L molecules fit more

tightly than S

• L over S: so L has ↑ D

CO2

If slope positive, solid more dense than the liquid

water

If slope negative, solid less dense than the liquid:

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Problem A. Sketch a phase diagram for a substance based on the following information: Normal BP = 110°C Normal FP = -22°C Triple point = -20 °C and 0.100 atm Critical point = 200°C and 150 atm

T °C P (atm)

G S L

• 20

0.100 200 150 1

• 22

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NFP NBP

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110

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TP

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CP

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Pressure atm

gas solid liquid

• 20

0.100 200 150 1

• 22

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NFP NBP

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110

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Triple pt

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Critical pt.

If a sample is placed in a container at 20°C and 0.98 atm, what phase(s) would exist? liquid The P of a sample is decreased from 140 atm to 0.095 atm at a constant T of 130°C and then the T is decreased from 130°C to -60°C at a constant P of 0.095 atm, what phase change(s) would take place?

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vaporization and deposition

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If a sample of solid is dropped into liquid, what would happen? L more D than S, ∴S floats

. .

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Which phase transitions could occur if a solid is heated at a pressure above its triple point?

Melting and vaporization

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P

Problem E.

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Water has several solid forms

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Do problem # 4 on PS 7.5 as independent practice in class

Problem set 7.5

Problem # 3