Read Matter: Track Particles, Temperature and Pressure
Phase-change questions become simple when you follow particle energy and spacing instead of memorising every diagram.
A phase change alters the arrangement and motion of particles without creating a new substance.
Particles change their freedom of movement
Heat → particles move more freely
Heating increases particle motion: solid → liquid → gas. During a phase-change plateau, energy separates particles instead of raising temperature.
Read a heating curve
A rising segment means temperature and particle kinetic energy increase. A flat segment means energy is changing the state while temperature remains constant. For water: 0 °C marks melting/freezing and 100 °C marks boiling at standard pressure.
Use the particle picture
Solid particles vibrate about fixed positions; liquid particles slide past one another; gas particles are far apart and move freely. Higher temperature means greater average kinetic energy.
Apply pressure correctly
A gas liquefies on cooling and/or compression. Sublimation is the direct solid ↔ gas change; camphor is a familiar example.
OlympIQ exam lens
- ✓Locate whether the graph is rising or flat.
- ✓Relate temperature to average kinetic energy.
- ✓Decide whether pressure or temperature is being changed.
Energy supplied during melting or boiling does not raise temperature; it is used to overcome attractions between particles.
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