Particle Model of Matter (P1)

Arrangement: SOLIDS

• Particles close together

• Regular pattern

• Vibrate but do not move from place to place

• Does not flow

Arrangement: LIQUIDS

• Particles close together

• No regular patterns

• Move around each other

• Flows

Arrangement: GASES

• Particles far apart

• No regular pattern

• Particles move very rapidly

• Flows

Density definition

Mass of an object for a given volume.

EQUATION: Density

P = m / v

→ P: density (kg/m²)

→ m: mass (kg)

→ v: volume (m³)

Density: SOLIDS

• Very high density → particles packed closely together → lot of mass for their volume

Density: LIQUIDS

• High density → particles close together, high mass for their volume

Density: GASES

• Low density → particles far apart → small mass for their volume

Mass during change of state

Mass is conserved.

→ Physical changes are reversible, chemical changes are not.

Internal energy definition

Energy stored in a system by particles

→ includes:

• kinetic energy (due to movement)

• potential energy (forces between particles and bonds between atoms / molecules

Sublimation (change of state)

Solid → gas

Evaporation on surface of liquid

When a liquid evaporates (turns to a gas), only the particles on the surface have enough energy to change state

Heating a system

Heating increases energy of particles → increase the internal energy = raise in temperature OR change of state

Specific heat capacity

The amount of energy required to raise the temperature of 1kg of a substance by 1°C

Heating graph

1. Temperature of solid rises as we heat it → increasing energy of particles

2. Eventually, temperature stops rising → horizontal line → solid is changing state (melting)

   → Energy being put in is weakening / breaking forces of attraction between particles → change in state

   → During change of state, internal energy store increases but temperature stays constant

3. Then, temperature starts to rise again → increasing energy of particles

4. Line becomes horizontal again → liquid now boils (change in state) → energy put in is weakening / breaking forces of attraction between particles

Specific latent heat definition

Amount of energy required to change the state of 1kg of a substance with no change in temperature

→ OF FUSION: solid to liquid

→ OF VAPORISATION: liquid to vapour

EQUATION: Specific latent heat

E = m x L

→ E: energy for change in state (J)

→ m: mass (kg)

→ L: specific latent heat (J/kg)

Pressure of gas is due to… and can be increased by…

Particles colliding with the walls of the container it is held in

• by increasing temperature → increasing kinetic energy → therefore number of collisions per second OR energy of each collision

• decreasing volume of container → more particles present in smaller volume → decreased distance of particles before colliding → increased collisions per second

Pressure of a gas is decreased when…

• increasing the volume of the container (while keeping temp. constant) - increased spacing between particles and bonds → they travel further before colliding with walls

Kinetic energy of gases in low temperatures

Particles have lower kinetic energy → fewer collisions per second → lower energy collisions → low pressure

Kinetic energy of gases in high temperatures

Particles have higher kinetic energy → more collisions per second → higher energy collisions → high pressure

Doing work on gas pressure

Doing work on gas, such as compression = transferred energy to gas particles → increasing internal energy (kinetic + potential energy) → increasing temperature of gas