Phase Changes

LIQUID Solid Phases of Matter PLASMA GAS The FOUR states of matter are determined by the amount of …………………. available. + + + + + +

LIQUID Solid Phases of Matter INCREASING ENERGY PLASMA GAS The FOUR states of matter are determined by the amount of ENERGY available. + + + + + +

Phases of Matter ENERGY/ Movement FORCES POSITION/ ArrangementShape PLASMA GAS LIQUID SOLID

Phases of Matter High – particles breaking up High – Rapid random motion Higher Slide over each other Low energy vibrate ENERGY/ Movement None Very weak Weakened Very Strong FORCES Changing Random Fill any container Random Take shape of container Fixed POSITION/ ArrangementShape PLASMA GAS LIQUID SOLID

LIQUID Solid Phase changes GAS
Think about what is involved when a substance has to change from one phase to another . Name each process and describe what needs to happen in terms of:
position of and spaces between particles
forces between particles
energy of particles.

Phase Changes Process ENERGY FORCES PARTICLE (positions) Solid  GAS Liquid  Gas Solid  Liquid

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
When 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).
Condensing Energy given off Energy given off Liquid Gas The temperature stays constant because strengthening forces releases energy which replaces that which has been removed.

Freezing
When 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 - Snow
Explain why the air is warmer when it snows than when the snow is thawing (melting).

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 Process ENERGY FORCES PARTICLE (positions) Solid  GAS Liquid  Gas Solid  Liquid

Boiling vs Evaporation
Low Temp
Energy taken out.
Not affected by pressure.
High Temp
Energy put in
Affected by atmospheric pressure
Differences
Change water to water vapour
Particles undergo same changes (increase spaces, energy, weaker forces)
Similarities Evaporation Boiling

Heating Curve 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.

Phases Task
Find out the melting point and boiling points of the following substances.
Hydrogen oxide (H 2 O) Mp: 0 o C, Bp: 100 o C
Nitrogen - gas 80% of the air
(N 2 ) Mp: -210 o C, Bp: -195 o C
Mercury - liquid Mp: -39 o C, Bp: 357 o C
What factors can affect the boiling point of water?
Altitude (pressure) - higher (alt) --> lower (bp)
Dissolved substances --> raise the boiling point.

Phase Changes

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