4PH1

Changes of State

Solids, Liquids & Gases · 2 question types

Practise

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable
Low
Stable6%

Specific heat capacity, specific latent heat and heating/cooling curves tested consistently.

The three states of matter

  • All ordinary matter exists in one of three states at typical temperatures: solid, liquid or gas
  • The state determines whether the material has a fixed shape, a fixed volume, and how easily it flows or compresses

Particle behaviour in each state

  • Solid
    • Particles are packed tightly in a regular pattern (a lattice)
    • Each particle vibrates about a fixed position; it cannot move past its neighbours
    • The material has a definite shape and a definite volume
  • Liquid
    • Particles are still in contact but no longer locked into a lattice; they move freely past one another
    • The material has no definite shape (it flows to fit the bottom of any container) but still has a definite volume
  • Gas
    • Particles are far apart with mostly empty space between them
    • Particles move rapidly and randomly in all directions
    • The material has no definite shape and no definite volume; it expands to fill any container it is placed in
    • Gases are easily compressed because the large gaps between particles can be squeezed out
A solid keeping its own fixed shape and volume, a liquid taking the shape of its container while keeping a fixed volume, and a gas expanding to completely fill its container
Source: Solids, Liquids & Gases by Save My Exams
PropertySolidLiquidGas
DensityHighSlightly lower than solidVery low
Particle arrangementRegular latticeClosely packed but disorderedFar apart, randomly arranged
Particle motionVibrate about fixed positionsSlide past each otherMove rapidly in all directions
Particle energyLowHigher than solidHighest
Definite shape?YesNoNo
Definite volume?YesYesNo
Easily compressed?NoNoYes
Exam tip

Describing particle arrangement and motion

What comes up: "describe the arrangement and motion of particles in a solid / liquid / gas".

Watch out: use precise wording — for a liquid, say particles "flow past each other" / "move randomly", not the vague "move freely"; for a solid, state they vibrate about fixed positions (just "fixed positions", with no mention of vibration, misses the motion mark).