Unless otherwise stated, all images in this file have been reproduced from:
Blackman, Bottle, Schmid, Mocerino and Wille,
Chemistry, 2007 (John Wiley)
ISBN: 9 78047081 0866
e
CHEM1002 [Part 2]
A/Prof Adam Bridgeman (Series 1)
Dr Feike Dijkstra (Series 2)
Weeks 8 – 13
Office Hours:
Room:
e-mail:
e-mail:
Monday 2-3, Friday 1-2
543a
adam.bridgeman@sydney.edu.au
feike.dijkstra@sydney.edu.au
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Physical States and Phase Diagrams
Lecture 5:
•
Periodic Trends
Lecture 6:
•
Physical States: Gases, Liquids and Solids
•
Phase Changes
•
Phase Diagrams
•
Supercritical Fluids
•
Blackman, Chapter 7, Sections 7.1 and 7.3
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•
•
•
•
•
Phase Changes: ΔpcH
As heat is added to a solid, the molecules vibrate more and more, until....
The solid melts - an endothermic change as bonds are broken
As heat is added to the liquid, the molecules move more and more, until....
The liquid boils - an endothermic change as bonds are broken
As heat is added to the gas, the molecules move faster and faster
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Normal Melting and Boiling Points
• Vapour pressure: pressure exerted by vapour in
equilibrium with its solid or liquid at stated
temperature.
• Normal melting point: melting point when pressure
equals 1 atm (101.3 kPa).
• Normal boiling point: temperature where vapour
pressure of liquid equals 1 atm.
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Phase Diagrams
• Give temperatures and pressures where the different
phases are stable.
• In a one-component system, there 3 phases (solid, liquid, gas):
 3 two-phase equilibria
liquid-gas, solid-liquid, solid-gas
 1 three-phase equilibrium
all three phases co-exist: triple point
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Construction of a Phase Diagram I
• Plot vapour pressure of liquid as function of T
(unique pressure where both phases exist at given T – co-
existence curve of liquid and gas):
Pressure
vapour pressure = external pressure
liquid
gas
Temperature
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Construction of a Phase Diagram II
Plot melting point of solid as function of pressure
(co-existence curve of liquid & solid):
Pressure
•
solid
liquid
Temperature
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Construction of a Phase Diagram III
• Plot vapour pressure between solid and gas
(unique pressure where both phases exist at given T –
co-existence curve of solid & gas):
Pressure
e
solid
gas
Temperature
• Putting these all together gives phases at different P, T
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Construction of a Phase Diagram
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Phase Diagram for CO2
solid
1 atm
liquid
• At 298 K and 1 atm,
 CO2 is a gas
 decreasing the
temperature, leads to
deposition to solid:
 increasing the pressure
leads to condensation to
liquid
sp = 195 K
gas
298 K
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Phase Diagram for CO2
solid
liquid
gas
• On solid /liquid
boundary,
increasing
pressure leads to
formation of more
solid
• Solid is more
dense than the
liquid.
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Phase Diagram for H2O
solid
liquid
273.15 K
1 atm
373.15 K
gas
• Starting at 1 atm and warming from T < 273 K,
 ice melts at 273.15 K (normal melting point)
 water boils at 373.15 K (normal boiling point)
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Phase Diagram for H2O
solid
liquid
gas
• Triple point: three phases co-exist only at single P,T :
the Kelvin scale defined is by 273.16 K = temperature at
which water is at triple point
• Note: Ttriple point is slightly higher than Tnormal melting
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The Unusual Properties of Water
• The solid-liquid slope for H2O is negative:
 ice melts if the pressure is increased at fixed temperature
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Critical Temperature and Pressure
• T & P at which boundary between liquid and vapour
disappears.
• If sealed tube of CO2 liquid and vapour heated, liquid-vapour
phase boundary disappears at 31 °C and 73 atm:
vapour
T > 31 °C
supercritial
fluid
liquid
no phase boundary:
cannot say that it is
either liquid or vapour
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Supercritical Fluids
 Supercritical fluids: substance above critical temperature
(Tc).
 Can behave as solvents dissolving a wide range of
substances.

New industrial reaction medium.
 Used in dry-cleaning and food production (e.g. caffeine
extraction).
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Practice Examples
A.
B.
C.
D.
E.
(i) only
(ii) only
(iii) only
(i) and (ii)
(i) and (iii)
Pressure
1. Which of the following statements concerning the phase diagram below
is/are correct?
(i). Moving from point A to B results in a phase transition from solid to liquid.
(ii).Point D lies at the critical point.
(iii).At point C, liquid and gas phases coexist in equilibrium.
B
A
C
D
Temperature
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Practice Examples
2. The gas methane, CH4, has a critical point at –82 °C and 46 atm. Can
methane be liquefied at 25 °C? Explain your answer. (2008-J-3)
3.
Which of the following gases can be liquefied at 25 °C?
Gas
Critical point
CH3Cl 144 °C, 66 atm
SO2
158 °C, 78 atm
CH4
–82 °C, 46 atm
(A) SO2 only
(B) CH4 only
(C) CH3Cl and SO2
(D) all of them
(E) none of them
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Practice Examples
4. You may recall from a lecture demonstration or your laboratory work
that solid CO2 sublimes under ambient conditions while ice melts.
Define the terms sublimation and melting.
5. What is a triple point (e.g. in the phase diagram of CO2 or H2O)?
6. What does the different behaviour of ice and solid CO2 indicate about
the relative positions of their respective triple points?
2007-N-6
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Summary: Phase Diagrams
Learning Outcomes - you should now be able to:
•
•
•
•
Complete the worksheet
Identify and explain the types of intermolecular
and intramolecular forces
Define and give two examples of allotropes
Answer Review Problems 6.28-6.32 and 7.5-7.7
in Blackman
Next lecture:
•
2 component phase diagrams and entropy
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