11 Melting & Boiling

8/7/2019 11 Melting & Boiling

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MELTING

&BOILING

TOPIC 11: THERMAL PROPERTIES OF MATTER

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WHAT HAPPENS TO MATTER

WHEN THERMAL ENERGY IS

APPLIED TO IT?

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OF THE MATTER

THERMAL ENERGY

CAN

Changethe temperature

Changethe state

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WHAT DO WE KNOW?

When heat is applied to a substance.The substance may undergo changes of state.

Heat Energy Applied

Change in Stateof substance

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WHAT DO WE KNOW?

When heat is removed from a substance.The substance may undergo changes of state.

Heat Energy Removed

Change in Stateof substance

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FOCUSON

THESUBSTANCEmELTING&BOILING

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MELTING

A change of state from solid to liquid without a

change in temperature.

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SOLID LIQUID

MELTING


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m.p = -117 C

Et

hly

Alc

oho

l

m.p = 0 C

Ice

m.p = 57 C

W

ax

For a puresubstance, melting

occurs at afixedtemperature.

This temperatureis known as

the melting point.

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m.p = 232 C

Tin

m.p = 1060 C

Gold

For a puresubstance, meltingoccurs at a

fixedtemperature.


the melting point.

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DETERMINATION OF MELTING POINT

The solid is slowly heated until all the solid melts.

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Procedures

Record the initial temperatureof the solid.1

Start heating with a slow

flame from a Bunsen burner.2


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Procedures

Take readings of

temperature every minute

until all the solid has melted

and the temperature of the

liquid reaches a certaintemperature.

3


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Procedures

Plot a graph of temperature

against time.4


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-10

0

10

20HEATING CURVE OF ICE

Tem

perature/

C

Time / min


The graph is a smooth curvewith a horizontal section.

Heating curves are used to

determine melting points.

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-10

0

10

20HEATING CURVE OF ICE

Tem

perature/

C

Time / min


The horizontal lineindicatesa change of state.

Refer to the temperature

axis for the melting point!

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SOLIDIFICATION

A change of state from liquid to solid without a


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SOLID LIQUID

FREEZING


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Napthalene

freezing pt = 79 C

Forapure substance,freezing occursat a

fixedtemperature.


the freezing point.

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DETERMINATION OF FREEZING POINT

The liquid is slowly cooled until all the liquid freezes.

Procedures

Record the initial temperature

of the liquid.1

Take readings of temperature

every minute until all the liquid

freezes and the temperature ofthe solid reaches a certain

temperature.

2

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The liquid is slowly cooled until all the liquid freezes.

Procedures

Plot a graph of temperatureagainst time.

3

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65

70

75

80

85

90

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

COOLING CURVE OF NAPTHALENE

Temperature/

C

Time / min


Cooling curves are used to

determine freezing points.

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65

70

75

80

85

90

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18


Temperature/

C

Time / min


The horizontal lineindicatesa change of state.


axis for the freezing point!PreparedbyCg




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65

70

75

80

85

90

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18


Temperature/

C

Time / min



axis for the freezing point!

Freezing point isthe temperature atwhich a liquid changes to a solid.

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MELTING POINT & FREEZING POINT

A pure substance will solidify/ freeze at atemperature equal to its melting point.

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SOLID LIQUID

MELTING

FREEZING

Melting Point

of Substance

Freezing Point

of Substance=


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BOILING

A change of state from liquid to gas without a


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LIQUID GAS

BOILING


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For a pure substance, boiling occurs ata

fixedtemperature.


the boiling point.

b.p = 35 C

Ether

b.p = 79 C

Alcohol

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For a pure substance, boiling occurs ata

fixedtemperature.


the boiling point.

b.p = 357 C

Mercury

b.p = 100 C

Water

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DETERMINATION OF BOILING POINT

-10

1030

50

70

90

110HEATING CURVE OF WATER

Temperature/

C

Time / min

Heating curves arealso used to determine

boiling points.

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-10

1030

50

70

90


Temperature/

C

Time / min

These horizontal linesindicate

changes of state.

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-10

1030

50

70

90


Temperature/

C

Time / min

Theupper horizontallinesindicateliquid to

gasconversion

Refer to thetemperature axisfor the boiling

point!

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-10

1030

50

70

90


Temperature/

C

Time / min

Thelower horizontallinesindicatesolid to

liquidconversion

Refer to thetemperature axisfor the melting

point!

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CONDENSATION

A change of state from gas to liquid without a




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LIQUID GAS

CONDENSATION


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LIQUID GAS

CONDENSATION

BOILING

BOILING POINT & CONDENSATION POINT

A pure substance will condense at a temperatureequal to its boiling point.

Condensation Point

of Substance

Boiling Point of

Substance=


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WHY IS

THE TEMPERATURECONSTANT DURING

CHANGES OF STATE?PreparedbyCgEdnaMariaHjOsman.E-m


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LATENT HEATAll the thermal energy is used to break/create the

substances intermolecular bonds during changes of state.



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SOLIDLIQUIDGAS

CreatingBonds

CreatingBonds

Breaking

Bonds

Breaking

Bonds

None of the thermal energy is used to change the kinetic

energy of the particles during changes of state.

There will be no change in the temperature of the substance.

SUMMARIZATION


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SUMMARIZATION

-10

10

30

50

70

90

110

A HEATING CURVE

Te

mperature/

C

Time / min

Boiling

Melting

Solid &

LiquidPresent

Liquid &Gas

Present

LiquidPresent

SolidPresent



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SUMMARIZATION


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MELTING POINT & FREEZING POINTA pure substance will solidify/ freeze at a

temperature equal to its melting point.



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SOLID LIQUID

MELTING

FREEZING

Melting Point

of Substance

Freezing Point

of Substance=

SUMMARIZATION


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11 Melting & Boiling

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