Heating and Cooling Curve

HEATING AND HEATING AND COOLING CURVECOOLING CURVE

CHAPTER 2

OBJECTIVESOBJECTIVES

At the end of this lesson we should be At the end of this lesson we should be able to :able to :

a) elaborate the changes state of the a) elaborate the changes state of the substances by using the kinetic theory substances by using the kinetic theory

model model b) differentiate the heating and cooling b) differentiate the heating and cooling

curves of the naphthalene curves of the naphthalene

KINETIC THEORY IN THE KINETIC THEORY IN THE CHANGES OF STATES OF CHANGES OF STATES OF MATTERMATTER

A substances can be changed from one A substances can be changed from one state into another when it is heated or state into another when it is heated or cooledcooled

The changes in the state of the The changes in the state of the substances can be explained using the substances can be explained using the kinetic theory modelkinetic theory model

The changes of states of The changes of states of mattermatter

Heating upHeating up

Process Process

MeltingMelting

solidsolid

liquidliquid

evaporatingevaporating liquidliquid gasgas

Cooling Cooling down down

condensingcondensing gasgas liquidliquid

freezingfreezing liquidliquid solidsolid

Changes

cooling cooling

heating heating

solid liquid gas

SolidSolid LiquidLiquid GasGas

particles packed particles packed closely closely solid heated, solid heated, particles receive heat particles receive heat energy, kinetic energy, kinetic energy increases energy increases vibrates fastervibrates faster at melting point, at melting point, particles vibrate so particles vibrate so much, break away much, break away from the fixed from the fixed positions. Solid positions. Solid become liquidbecome liquid Melting point = Melting point = temperature at which temperature at which the solid changes into the solid changes into the liquid statethe liquid state

when liquid continuously heated when liquid continuously heated particles receive > E & move fasterparticles receive > E & move faster collide each other > oftencollide each other > often at boiling point, particles receive at boiling point, particles receive enough E to overcome the forces of enough E to overcome the forces of attraction holding them together. attraction holding them together. Particles in liquid state break loose Particles in liquid state break loose become gaseous statebecome gaseous state when liquid cooled, movement of when liquid cooled, movement of particles slows down. Stronger forces particles slows down. Stronger forces attraction btwn particles formedattraction btwn particles formed particles arranged in orderly manner particles arranged in orderly manner in solid state. Process of liquid in solid state. Process of liquid solid=solidification, T of this process= solid=solidification, T of this process= freezing pointfreezing point Melting point & freezing point of a Melting point & freezing point of a substance have same valuesubstance have same value

gas cooled particles gas cooled particles lose kinetic E, lose kinetic E, movement of particles movement of particles slows downslows down forces of attraction forces of attraction btwn particles formed btwn particles formed which hold the particles which hold the particles together in liquid statetogether in liquid state condensation= condensation= process of gas process of gas liquidliquid T of this process T of this process same as boiling pointsame as boiling point

heating heating

cooling cooling

MELTING POINT & MELTING POINT & BOILING POINTBOILING POINT

No two substances have the same melting and No two substances have the same melting and boiling pointboiling point

The melting & boiling points of a substance will The melting & boiling points of a substance will change when there is a small amount of impurity change when there is a small amount of impurity in itin it

Example; melting point of pure water is 0Example; melting point of pure water is 0°C and °C and its boiling point is 100°C. A small amount of salt its boiling point is 100°C. A small amount of salt added to the water will decrease its melting point added to the water will decrease its melting point to -2°C and increase its boiling point to 102°C to -2°C and increase its boiling point to 102°C

HEATING CURVE OF HEATING CURVE OF NAPHTHALENENAPHTHALENE

80°C

A

B C

D

time (s)

temperature (°C)

Region in Region in the graphthe graph

State of substances and the State of substances and the energy changeenergy change

Region ABRegion AB naphthalene in solid statenaphthalene in solid state as it is heated, heat energy as it is heated, heat energy

converted to kinetic energyconverted to kinetic energy kinetic energy increases and kinetic energy increases and

molecules vibrate faster about their molecules vibrate faster about their

fixed positions fixed positions T increases as the molecules T increases as the molecules

receive more heat Ereceive more heat E



Point BPoint B as kinetic E of molecules increases, as kinetic E of molecules increases,

the molecules vibrate faster. At point the molecules vibrate faster. At point

B, the molecules vibrate so much that B, the molecules vibrate so much that

they break away from fixed positionsthey break away from fixed positions the solid naphthalene begins to meltthe solid naphthalene begins to melt


State of substances and State of substances and

the energy changethe energy changeRegion BCRegion BC naphthalene now consists of a mixture of naphthalene now consists of a mixture of

solid and liquid solid and liquid at this region the temperature remains at this region the temperature remains

constant because the heat energy supplied is the constant because the heat energy supplied is the

same amount as the heat energy absorbed same amount as the heat energy absorbed heat energy absorbed to overcome the forces of heat energy absorbed to overcome the forces of

attraction holding the naphthalene molecules attraction holding the naphthalene molecules

together in the solid statetogether in the solid state the heat absorbed to overcome the forces of the heat absorbed to overcome the forces of

attraction is called the latent heat of fusionattraction is called the latent heat of fusion latent heat of fusionlatent heat of fusion of a substance = heat of a substance = heat

required to convert a solid into a liquid without a required to convert a solid into a liquid without a

change in temperaturechange in temperature



Point CPoint C

Region CDRegion CD

all the naphthalene has completely all the naphthalene has completely

meltedmelted

naphthalene is in liquid statenaphthalene is in liquid state as liquid naphthalene heated, the as liquid naphthalene heated, the

molecules gain more heat energymolecules gain more heat energy the temperature continues to the temperature continues to

increaseincrease

COOLING CURVE OF COOLING CURVE OF NAPHTHALENENAPHTHALENE

80°C

time (s)

temperature (°C)

P

Q R

S



Region PQRegion PQ naphthalene in liquid statenaphthalene in liquid state liquid naphthalene loses heat to the liquid naphthalene loses heat to the

environmentenvironment kinetic energy of molecules kinetic energy of molecules

decreases as temperature decreases decreases as temperature decreases



Point QPoint Q as kinetic energy molecules as kinetic energy molecules ↓ , the ↓ , the

molecules move slower molecules move slower at point Q, the molecules stop at point Q, the molecules stop

moving except for small vibrationsmoving except for small vibrations at this point, the liquid naphthalene at this point, the liquid naphthalene

begins to solidify or freezebegins to solidify or freeze



Region QRRegion QR naphthalene now consists of a naphthalene now consists of a

mixture of liquid and solid mixture of liquid and solid at this region the temperature at this region the temperature

remains constant because the heat remains constant because the heat

energy lost to the environment is the energy lost to the environment is the

same amount as the heat energy same amount as the heat energy

released released latent heat of fusion is released when latent heat of fusion is released when

forces of attraction are formed forces of attraction are formed

between the molecules as the liquid between the molecules as the liquid

naphthalene solidify (or freezes)naphthalene solidify (or freezes)



Point RPoint R

Region RSRegion RS

all naphthalene has completely all naphthalene has completely solidifiedsolidified

naphthalene in the solid statenaphthalene in the solid state the solid naphthalene continues t the solid naphthalene continues t

lose heat to the environment and lose heat to the environment and

hence the temperature drops down to hence the temperature drops down to

room temperature room temperature

KINETIC THEORY MODEL

HEATING AND COOLING CURVE

MELTING POINT AND BOILING POINT

EXAMPLE

The concept of melting point and boiling point

The melting and freezing points of

naphthalene

MeltingBoiling/

evaporation

Freezing Condensation

Solid Liquid Gas

QUIZQUIZ1. Which processes are correct based on below 1. Which processes are correct based on below

table that shows the change of physical states table that shows the change of physical states and change of energies of four substances?and change of energies of four substances?

Name of Name of processprocess

Change of Change of physical statephysical state

Change of Change of energyenergy

AA CondensationCondensation Gas to liquidGas to liquid Heat is absorbedHeat is absorbed

BB Melting Melting Solid to liquidSolid to liquid Heat is absorbedHeat is absorbed

CC EvaporationEvaporation Liquid to gasLiquid to gas Heat is given outHeat is given out

DD Condensation Condensation Solid to gasSolid to gas Heat is given outHeat is given out

Answer = B

2. Which of the following correctly describes the 2. Which of the following correctly describes the particles in a concentrated sugar solution? particles in a concentrated sugar solution?

Sugar moleculesSugar molecules Water moleculesWater molecules

A.A. Widely separated, move Widely separated, move randomlyrandomly

Close together, move Close together, move randomlyrandomly

B.B. Close together, move Close together, move randomlyrandomly

Close together, move Close together, move randomlyrandomly

C.C. Close together, move Close together, move randomlyrandomly

Widely separated, move Widely separated, move randomlyrandomly

D.D. Close together, not movingClose together, not moving Close together, move Close together, move randomlyrandomly

Answer = C

3.3. Which graph is true that showing the heating and Which graph is true that showing the heating and

cooling curve of naphthalene? cooling curve of naphthalene?

I IIIII IV

A. I & II

B. I & III

C. II & III

D. I & IV

100°C100°C

80°C80°C

Answer = C

Heating and Cooling Curve

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