Kinetic Particle Theory

What is Kinetic Particle Theory

The kinetic particle theory states that

all matter is made up of tiny particles and that these particles

are in constant, random motion.

Uses of the Kinetic Particle Theory

• Describes the states of matter• Explains the differences in the

properties of solids, liquids and gases

• Explains the changes of states

Three States of Matter

ICE WATER STEAM

Solid Liquid Gas

Particles and properties

Properties of Solid, Liquid & Gas

Properties Solid Liquid GasSample picture of how the particles are arrangedShape

Volume

Compressibility

Fixed

Fixed Fixed

Not fixed

Not fixed

Not fixed

Cannot be compressed

Cannot be compressed

Can be compressed

How do particles move?

Properties Solid Liquid GasMotion of molecules

Arrangement of molecules

Intermolecular forces

Distance between molecules

Energy of the particles

Vibrations about fixed position only

Arranged in fixed and orderly

arrangement

Slide past & movement

through liquid

No fixed arrangement

Vibrations and movement anywhere

No fixed arrangement

Very strong Weak Negligible

Packed very close together

Not so closely packed Very far apart

According to Kinetic Particle Theory

Less energy than liquids or gases

More energy than solids but less than gases

More energy than solids or liquids

Properties Solid Liquid GasShape

Reason: Reason: Reason:

VolumeReason: Reason: Reason:

CompressibilityReason: Reason: Reason:

Fixed

Fixed Fixed

Not fixed Not fixed

Not fixed

Cannot be compressed Cannot be compressed Can be compressed

• Particles are held together by strong forces of attraction.

• Vibrate about fixed positions & cannot move about freely.

• Particles are held together by weaker attractive forces

• Not held in fixed positions• Move freely by sliding over

one another

• Forces of attraction between particles are very weak

• Not held in fixed positions• Move rapidly in any

direction

• Particles are packed very close to one another

• Particles are packed very close to one another

• Almost no empty spaces between particles

• Particles are further away from one another

• Particles are still packed quite closely together

• Particles are further away from one another

• Particles are still packed quite closely together

• Large space between particles

• Can be forced to move closer together

• Large space between particles

• Can be forced to move closer together

Relating Properties of Solid, Liquid & Gas to the Kinetic Particle Theory

Cornflour paste: solid or liquid?

Multiple-choice quiz

Changes of StateIs it reversible?

SOLID

LIQUID GAS

1. MELTING

Changes of State

1. MeltingWhat happens to the particles of a solid that is heated until it melts?

As heat energy is supplied to the solid and converted into kinetic energy, the particles vibrate faster about their fixed positions.

When the vibrations of the particles overcome the attractive forces between them, they begin to break away from their fixed positions.

The particles slide over one another and the substance is now a liquid.

Heat energy

Heating Curve (Melting)Temperature/oC

Time/min

A B: Solid heats up. The temperature of the solid increases until it reaches point B, its melting point. At point B, the solid begins to melt.

B C: Solid melts. A mixture of solid and liquid exists here. During the melting process, the temperature of the substance remains constant even though heating continues. All the heat energy taken in by the particles is used to overcome the forces of attraction between particles.

C D: Liquid heats up. At point C, all the solid has melted and the temperature of the liquid rises as heating continues.

SOLID

LIQUID GAS

2. FREEZING

1. Melting

Changes of State

2. Freezing

Energy is given out by the particles of the liquid. They lose kinetic energy and begin to move more slowly.

When the temperature is low enough, the particles do not have enough energy to move freely. Some particles start to settle into fixed positions.

Finally, all the particles settle into fixed positions. Particles can only vibrate about their fixed positions. The substance is now a solid.

What happens to the particles of a liquid that is cooled until it freezes?

Cooling Curve (Freezing)

Temperature/oC

Time/min

P – Q: Liquid cools.The temperature of the liquid drops until it reaches point Q, the freezing point of naphthalene. At point Q, the liquid starts to freeze.

Q – R: liquid freezes.A mixture of liquid and solid exists here. During the freezing process, the temperature of the substance remains constant even though cooling continues.

R – S: solid cools. At point R, the substance has solidified. The temperature of the solid continues to drop as it is cooled.

SOLID

LIQUID GAS

3. Evaporation / Boiling

2. Freezing

1. Melting

Changes of State

3. Boiling

As the liquid is heated, the particles gain kinetic energy and start to move faster.

Eventually, the particles have enough energy to overcome the attractive forces holding them together.

They spread far apart and move rapidly in all directions. The substance is now a gas.

Heating Curve (Boiling) Temperature/oC

Time/min

When a liquid is heated, its temperature increases till its boiling point is reached.

Here, it boils and changes into a vapour.

Temperature remains constant till all the liquid has boiled off. Heat energy taken in is used to overcome forces of attraction between the particles of the liquid and to make the particles move further apart.

X

Y

The temperature remains constant till all the liquid has boiled off

Z

SOLID

LIQUID GAS

3. Evaporation / Boiling

2. Freezing

1. Melting

Changes of State

3. Evaporation

Evaporation occurs because some particles have enough energy (more kinetic energy) to escape as a gas from the surface of the liquid.

Volatile liquids are liquids that evaporate quickly at room temperature. E.g. Petrol and perfumes.

Differences between Evaporation & Boiling

Evaporation Boiling Occurs at temperatures

below boiling point

Occurs only at the surface of the liquid

Occurs slowly

• Occurs only at boiling point

• Occurs throughout the liquid

• Occurs rapidly

SOLID

LIQUID GAS4. Condensation

3. Evaporation / Boiling

2. Freezing

1. Melting4. Sublimation

Changes of State

4. Condensation

• Condensation occurs when a gas is cooled sufficiently to change into a liquid.

Eventually, the movement of the particles becomes slow enough for the gas to change into a liquid / move closer to slide past one another.

Heat energy is given out, and the gas particles lose energy and move more slowly as the temperature drops.

4. Condensation

SOLID

LIQUID GAS4. Condensation

3. Evaporation / Boiling

2. Freezing

1. Melting

4. Sublimation

5. Condensation

Changes of State

5. Sublimation

Dry ice sublimes

• Sublimation involves changing solids directly into a gas without going through the liquid state.

• Examples of substances undergoing sublimation:

1. Dry ice (Solid carbon dioxide)

2. Solid Iodine3. Ammonium Chloride4. Naphthalene (Moth ball)

5. Sublimation

• Occurs because particle at the surface have enough energy to break off from the solid and become gas

SOLID GAS

Solid iodine Iodine vapour

A substance sublimes because the forces between the particles in the liquid state are too weak to remain in this state.

Summary

Mixture of Solid & Liquid

Mixture of Liquid &

Gas

SOLID LIQUID GAS

MELTING POINT

BOILING POINT

SummaryHeat

Absorbed(endothermic)

Heat given out

(Exothermic)Process involved

MeltingBoiling

EvaporationSublimation

FreezingCondensation