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Unit 2: States of matter, atoms and compounds

Explaining Changes Of State — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 10 3 quizzes

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

2.3 Explaining Changes Of State — HIA INTERNATIONAL notes: Use particle theory and energy transfer to explain heating, melting, boiling, condensing and freezing.Expansion — solids expand when heated.Energy transfer — heat energy is transferred to the particles.Vibration — the mor…

  • Strong heating
  • Break-up of pattern
  • Liquid particles
  • Evaporation
  • Gas particles
  • Cold surface

Part 1 of 8Heating solids

Expansion
  • Expansion solids expand when heated.
Energy transfer
  • Energy transfer heat energy is transferred to the particles.
Vibration
  • Vibration the more energy the particles have, the more they vibrate.
Space
  • Space particles vibrating more take up more space.
Forces
  • Forces particles are still held in position by attractive forces.

Part 2 of 8Melting

Strong heating
  • Strong heating more heat energy is transferred to the particles.
Break-up of pattern
  • Break-up of pattern vibrations become so large that attractive forces cannot hold a fixed pattern.
Movement
  • Movement particles can slide past one another, not just vibrate.
Contact
  • Contact forces are still strong enough to keep the particles touching.

Part 3 of 8Boiling and evaporation

Boiling and evaporation
Liquid particles
  • Liquid particles they touch each other and are held together weakly.
Energy
  • Energy particles move more as heat energy is transferred.
Escape
  • Escape some particles have enough energy to break the weak attractive forces.
Result
  • Result these particles move freely and escape as gas.
Boiling
  • Boiling it happens throughout the liquid at the boiling point.
Evaporation
  • Evaporation it happens only at the surface and at any temperature below boiling.
  • It is faster when warmer, windier or with a larger surface area.

Part 4 of 8Condensing

Condensing
Gas particles
  • Gas particles free to move anywhere with no forces holding them.
Cold surface
  • Cold surface heat energy transfers from the particles to the surface.
Result
  • Result the particles move less and get closer together, and form a liquid.

Part 5 of 8Freezing

Energy loss
  • Energy loss heat energy transfers from the particles to the surroundings.
Slower movement
  • Slower movement particles can no longer slide past one another.
Fixed pattern
  • Fixed pattern they can only vibrate and arrange in a fixed pattern to form a solid.

Part 6 of 8Energy and temperature on a curve

Flat section
  • Flat section during melting and boiling the energy supplied is used to overcome forces between particles.
Pure substance
  • Pure substance it has a sharp fixed melting point and boiling point.
Impure substance
  • Impure substance it melts over a range of temperatures.

Part 7 of 8Summary of changes

ChangeEnergyParticles afterwards
MeltingTaken inClose together but irregular, sliding past each other
FreezingGiven outRegular fixed pattern, vibrating
BoilingTaken inFar apart, moving fast in all directions
EvaporationTaken inEscape from the surface only
CondensationGiven outClose together, sliding past each other
SublimationTaken inFar apart, moving fast

Part 8 of 8Plotting a heating curve for ice

1
Put crushed ice below 0 °C in a beaker with a thermometer.
2
Heat gently, stirring constantly.
3
Record the temperature every 30 seconds.
4
Plot temperature against time and note the flat sections.

Key terms

TermMeaning
Heat energyEnergy transferred to or from the particles.
Attractive forceForce holding particles together.
ExpandGet bigger because particles take up more space.
CondenseChange from gas to liquid.
FreezeChange from liquid to solid.
BoilChange from liquid to gas throughout the liquid.

Avoid these mistakes

1
Saying particles expand when heated — they move further apart or vibrate more.
2
Saying a changing substance gets hotter — the temperature stays constant while the state changes.
3
Thinking mass changes in a change of state — mass stays the same.
4
Saying freezing takes in energy — freezing gives energy out.

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