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PHASE CHANGES:

Chap. 13: Day 4

Heat of Fusion

Heat of Vaporization

Phase Diagrams

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Heating/Cooling Curve

temperature = KINETIC E

phase (position) =

POTENTIAL E

Used to show the Energy changes associated with changes in phase

Why do the two phase changes take different amounts of energy?

3Enthalpy (kJ/ mol)

Heat of Fusion

Heat of Vaporization

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PHASE CHANGES:

Standard molar enthalpy of Fusion = (kJ/mol)

fus

The heat energy required to fuse (melt) one mole of a sample

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PHASE CHANGES:

Standard molar enthalpy of Vaporization = (kJ/mol)

Hvap

The heat energy required to vaporize one mole of a sample

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1. You place 985 g of water (1L) into a pan at 100 C. How much heat must be supplied to vaporize all the water?

2. The same amount ice is at 0 C. How much heat must be supplied to melt all the water?

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TWO ways to change PHASE

•Temperature

Pressure

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Almeltingpoints

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Boiling points: Liquid to Vapor

Water

12Phase DiagramsPhase Diagrams

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TRANSITIONS TRANSITIONS BETWEEN BETWEEN PHASESPHASESSection 13.10Section 13.10

Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line.

(At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)

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Phase Equilibria — WaterPhase Equilibria — Water

Solid-liquidSolid-liquid

Gas-Gas-LiquidLiquid

Gas-Gas-SolidSolid

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And depositswhen cooled

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Triple Point Triple Point — Water— Water

At the At the TRIPLE POINTTRIPLE POINT all all three phases are in three phases are in equilibrium.equilibrium.

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Phases Phases Diagrams—Diagrams—

Important Points Important Points for Waterfor Water

T(˚C)T(˚C) P(mmHg)P(mmHg)

Normal boil point Normal boil point 100100 760760

Normal freeze pointNormal freeze point 00 760760

Triple point Triple point 0.00980.0098 4.58 4.58

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Critical T and PCritical T and P

.

LIQUID

GAS

Pcritical

Hig

h P

ress

ure

High Temperature

Tcritical

Note that linegoes straight up

Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.

Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.

As P and T increase, you finally reach the

CRITICAL T and P

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Critical T and PCritical T and P

TTcc((ooC) PC) Pcc(atm) M ((atm) M (g/molg/mol))

HH22OO 374 374 218 (18) P 218 (18) P

Freon-12Freon-12 112112 41 (121) NP 41 (121) NP

(CCl(CCl22FF22))

COCO22 31 31 73 (44) NP 73 (44) NP

CHCH44 -82 -82 46 (16) NP 46 (16) NP

Notice that TNotice that Tcc and P and Pcc depend on depend on

intermolecular forces.intermolecular forces.

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23Phase Diagram for Water

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Solid-Liquid EquilibriaSolid-Liquid Equilibria

Raising the pressure at constant T causes water to melt.

The NEGATIVE SLOPE of the S/L line is unique to H2O. Almost everything else has positive slope.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint

LIQUID H2OICEfavored atlow P

favored athigh P

LIQUID H2OICEfavored atlow P

favored athigh P

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