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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

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e CHEM1002 [Part 2]

Dr Michela SimoneWeeks 8 – 13

Office Hours: Monday 3-5, Friday 4-5Room: 412A (or 416)Phone: 93512830e-mail: michela.simone@sydney.edu.au

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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

Physical States and Phase Diagrams

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e 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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e 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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e 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-gas1 three-phase equilibrium

all three phases co-exist: triple point

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• 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):

liquid

gas

Temperature

Pre

ssu

revapour pressure = external pressure

Construction of a Phase Diagram I

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e• Plot melting point of solid as function of pressure

(co-existence curve of liquid & solid):

liquid solid

Temperature

Pre

ssu

re

Construction of a Phase Diagram II

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e 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):

solid

gas

Temperature

Pre

ssu

re

• Putting these all together gives phases at different P, T

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e Construction of a Phase Diagram

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• 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

Phase Diagram for CO2

liquid

gas

solid

298 K

1 atmsp = 195 K

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e Phase Diagram for CO2

• On solid /liquid boundary, increasing pressure leads to formation of more solid

• Solid is more dense than the liquid.

liquid

gas

solid

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e Phase Diagram for H2O

liquid

gas

solid

1 atm

• 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)

273.15 K 373.15 K

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e Phase Diagram for H2O

• 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

liquid

gas

solid

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e 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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e 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:

T > 31 °C

no phase boundary: cannot say that it iseither liquid or vapour

vapour

liquid

supercritial fluid

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e 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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x1. 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.

A. (i) onlyB. (ii) onlyC. (iii) onlyD. (i) and (ii)E. (i) and (iii)

Practice Examples

Temperature

Pressure

A B

CD

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x2. 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)

Practice Examples

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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x 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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e 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