Physical change Describe the rearrangement of molecules that occurs during

physical changes e.g. the sublimation of iodine and the boiling of water; show using both labelled diagrams and equations how:o   molecules are separated  

o   disordering of particles due to breaking of intermolecular forces  

o   energy change are small in relation to chemical changes find energy values

o    mass and numbers of atoms and molecules as being conserved during these physical changes.

Phases of MatterPhases of Matter

PLASMAPLASMA+

++

+ +

+

The FOUR states of matter are determined by the amount of ………………….…………………. available.

Phases of MatterPhases of Matter

INC

RE

AS

ING

EN

ER

GY

INC

RE

AS

ING

EN

ER

GY

H2O

+

++

+ +

+

The FOUR states of matter are determined by the amount of ENERGYENERGY available.

• o   molecules are separated

•   spaces increase

• o   disordering of particles due to breaking of intermolecular forces  strong forces weak forces

• o   energy change are small in relation to chemical changes find energy values

• Energy of Vaporisation: 2270 kJ/kg

• 118 kcal to decompose 2 moles of H2O 493.7kJ = 13 713.9 kJ/kg

• o    mass and numbers of atoms and molecules as being conserved during these physical changes.

• H2O(s) H2O (l) no atoms or mass lost!

PLASMAPLASMA

Highly ordered

Highly disordered

Phases of Matter

SOLID LIQUID GAS PLASMAPLASMA

POSITION/ ArrangementShape

FORCES

ENERGY/ Movement

Phases of Matter

SOLID LIQUID GAS PLASMAPLASMA

POSITION/ ArrangementShape

FixedRandom Take shape of container

Random Fill any container

ChangingChanging

FORCES Very Strong Weakened Very weakNoneNone

ENERGY/ Movement

Low energy vibrate

Higher Slide over each other

High – Rapid random motion

High – High – particles particles breaking upbreaking up

Phase changesPhase changes– o   molecules are separated

–   spaces increase

– o   disordering of particles due to breaking of intermolecular forces  strong forces weakweak forcesforces

– o   energy change are small in relation to chemical changes find energy values

– Energy of Vaporisation (Physical change)

– H2 O(l) H2O (g) : 2270 kJ/kg

– Chemical Change 118 kcal to decompose 2 moles of H2O

– 493.7kJ = 13 713.9 kJ/kg

– H2 O(l) H2 (g) + O2 (g)

– o    mass and numbers of atoms and molecules as being conserved during these physical changes.

– H2 O(s) H2O (l) no atoms or mass lost!

Phase ChangesSolid Liquid Liquid Gas Solid GAS

Process

PARTICLE (positions)

FORCES Force

ENERGY

Phase ChangesSolid Liquid Liquid Gas Solid GAS

ProcessEvaporation or boiling

sublimation

PARTICLE (positions)

Random more random

Slide over each other completely free movement

Fixed random rapid completely free

FORCES Forces weakened Forces broken Broken

ENERGY Energy required/taken or put in

Melting (Fusion)When a solid melts the particles

need to undergo a number of changes:

Solid --> Liquid:– the spaces between the particles

increase– The energy of the particles

increases– The forces between the particles are

weakened

Each of these changes requires energy to be put in.

The temperature stays constant because the extra energy is being used to weaken the forces.

Melting

Boiling/(Evaporation)When a liquid boils the particles

need to undergo a number of changes:

Liquid --> Gas:– the spaces between the particles

increase– The energy of the particles

increases– The forces between the particles

are weakened

Each of these changes requires energy to be put in.

The temperature stays constant because the extra energy is being used to weaken the forces.

Boiling/ (Evaporation )

Liquid

Gas

Condensation

Condensing

Energy given offEnergy given off

Liquid

GasWhen a gas condenses:– the spaces between the

particles decrease.– The energy of the particles

decreases (move slower).– The forces between the

particles are strengthened.Each of these changes requires

energy to be taken out. (Given off).

The temperature stays constant because strengthening forces releases energy which replaces that which has been removed.

FreezingWhen a liquid freezes (fuses) the

particles need to undergo a number of changes:

Liquid --> solid:– the spaces between the particles

decrease.– The energy of the particles

decreases (move slower).– The forces between the particles

are strengthened.Each of these changes requires energy

to be taken out. (Given off).

Fusion

Energy taken out Energy taken out

The temperature stays constant because strengthening forces releases energy which replaces that which has been removed.

Phase Change - SnowExplain why the air is

warmer when it snows than when the snow is thawing (melting).

This energy is lost to the surrounding air as heat which makes it feel warmer.

Phase Change - SnowWhen water freezes to

form snow – the particles (water molecules) must lose energy.

This energy is lost to the surrounding air as heat which makes it feel warmer.

The reverse process makes it feel much colder when the snow begins to melt.

Boiling vs Evaporation

Wind

Water molecules (high energy) escape from the surface of the liquid.

The remaining particles have less energy - lower temperature

ENERGY IS REMOVED FROM THE WATER (Cooling Effect).

All liquids have their own vapour (gas).

This vapour has a pressure which increases with temperature.

When the vapour pressure equals the pressure outside the liquid the liquid boils.

GAS

LIQUID

IN BOILING ENERGY MUST

BE PUT IN.The temperature

of the water does not change as the energy is used to change

the phase.

Phase Changes

Wind

Forces between particles

(intermolecular) breaking.

GASOH

H

OH

H

OH

H

O H

H

OH

H

Bonds inside particles (intramolecular) do NOT break!

Boiling & evaporation are both phase changes – intermolecular bonding is involved in phase changes – intra molecular bonding is not.

Forces broken!

Molecule escapes!

High energy molecules escape!

Phase ChangesSolid Liquid Liquid Gas Solid GAS

Process

PARTICLE (positions)

FORCES

ENERGY

Boiling vs Evaporation

Boiling Evaporation

Similarities • Change water to water vapour• Particles undergo same changes (increase spaces, energy, weaker forces)

Differences • High Temp• Energy put in• Affected by atmospheric pressure

• Low Temp• Energy taken

out.• Not affected by

pressure.

Heating CurveHeating Curve Water

020406080

100

0 200 400 600Time (S)

Tem

pera

ture

(C)

During a phase change the energy is used to overcome forces between the particles and increase the spaces between them - the temperature stays the same so the graph is flat.

Ice - melting

Water heating up

Water boiling

Graph of temperature change vs time for the heating of a sample of ice.T

empe

ratu

re o

C

Phases Task• Find out the melting point and boiling points of

the following substances.

– Hydrogen oxide (H2O) Mp: 0oC, Bp: 100oC – Nitrogen - gas 80% of the air

• (N2) Mp: -210oC, Bp: -195oC

– Mercury - liquid Mp: -39oC, Bp: 357oC

• What factors can affect the boiling point of water?– Altitude (pressure) - higher (alt) --> lower (bp)– Dissolved substances --> raise the boiling point.