3. Particle model of matter

Three states of matter

Solid, liquid, and gas.

Arrangement of particles in a solid

Particles are closely packed in a fixed, regular arrangement.

Arrangement of particles in a liquid

Particles are close together but randomly arranged and able to move past each other.

Arrangement of particles in a gas

Particles are spread far apart and moving freely in all directions.

Movement of particles in a solid

Particles vibrate around fixed positions.

Movement of particles in a gas

Particles move freely and randomly at high speeds.

Forces between particles in a solid

Strong forces hold the particles together in fixed positions.

Forces between particles in a gas

Forces between particles are very weak or negligible.

Limitations of the particle model

It does not show the forces between particles.

Limitations of the particle model

It assumes all particles are perfect spheres and of equal size.

Formula to calculate density

Density = Mass ÷ Volume (ρ = m ÷ V).

Units for density

Kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³).

Units for mass

Kilograms (kg) or grams (g).

Units for volume

Cubic metres (m³) or cubic centimetres (cm³).

Why gases are less dense than solids

In gases, particles are far apart, meaning fewer particles per unit volume, resulting in lower density.

Calculate the volume of a cube

Measure the length of one side and cube it: Volume = side³ (V = l³).

Calculate the volume of a cuboid

Multiply the length, width, and height: Volume = length × width × height (V = l × w × h).

Method to calculate the density of an irregular shaped object

Measure the object's mass using a balance. Submerge the object in a measuring cylinder of water and note the water displacement. Use the formula Density = Mass ÷ Volume.

State change from solid to liquid

Melting.

State change from solid to gas

Sublimation.

State change from liquid to solid

Freezing.

State change from liquid to gas

Evaporation or boiling.

State change from gas to liquid

Condensation.

Difference between evaporation and boiling

Evaporation occurs at the surface of a liquid at any temperature. Boiling occurs throughout the liquid at a specific temperature.

Mass conservation during state changes

The total mass remains the same because particles are not created or destroyed, only rearranged.

State changes

Considered physical changes because no new substances are formed, and the change is reversible.

Internal energy

The total energy stored by the particles in a substance due to their kinetic and potential energy.

Changes from heating a system

Temperature increase and a change of state.

Energy equation

Energy = Mass × Specific Heat Capacity × Temperature Change (ΔE = m × c × Δθ).

Change in energy units

Joules (J).

Specific heat capacity units

Joules per kilogram per degree Celsius (J/kg°C).

Change in temperature units

Degrees Celsius (°C).

Specific heat capacity experiment

Measure the mass of the metal block, insert a heater and thermometer, measure initial temperature, apply known electrical energy, record temperature rise and energy supplied, use ΔE = m × c × Δθ to calculate specific heat capacity.

Temperature-time graph

Shows how the temperature of a solid changes as it is heated and changes state, with plateaus at melting and boiling points.

Latent heat

The energy required to change the state of a substance without changing its temperature.

Latent heat vs specific latent heat

Latent heat refers to the total energy required for a state change; specific latent heat is the energy required per kilogram of a substance.

Specific latent heat of fusion

The energy required to change a solid to a liquid.

Specific latent heat of vaporisation

The energy required to change a liquid to a gas.

Energy equation for latent heat

Energy = Mass × Specific Latent Heat (E = m × L).

Specific latent heat units

Joules per kilogram (J/kg).

Effect of temperature change on gas

Increasing temperature increases pressure due to faster-moving particles colliding more frequently and forcefully with container walls.

Pressure-volume gas equation

Pressure × Volume = Constant (pV = constant).

Pressure units

Pascals (Pa).

Volume units

Cubic metres (m³).

Impact of doing work on gas

Doing work increases the internal energy of the gas, leading to a temperature increase.