3.1.11

Changes of State

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Changes of State

Changes of state are physical changes.

Illustrative background for Physical (not chemical) changeIllustrative background for Physical (not chemical) change ?? "content

Physical (not chemical) change

  • When a material changes state, it is able to recover its old properties if the change is reversed.
  • Some chemical reactions are also reversible.
  • However, some chemical reactions are irreversible.
    • In irreversible chemical reactions, the material would not be able to return to its original properties.
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Conservation of mass

  • When a substance changes state, its mass is conserved (stays the same).

Changes of State

Objects can change state from one state of matter to another. Melting and boiling are examples of changes of state.

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Melting - solid to liquid

  • If we heat a solid, the solid particles vibrate more energetically, until they have enough energy to overcome the forces between them.
  • This is when the solid melts (becomes a liquid).
  • The temperature needed for this to happen is the melting point.
  • Melting is sometimes also called fusion.
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Boiling - liquid to gas

  • If we heat a liquid, the liquid particles move more energetically until they have enough energy to escape completely from the forces between them.
  • The particles become a gas and move completely freely.
  • The temperature needed for this to happen is the boiling point. Boiling can be called vaporisation.
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Condensation - gas to liquid

  • When the temperature of a gas decreases to the boiling point, the strength of the forces between particles increases and the particles condense to become a liquid.
  • For the same material, its boiling point is the same as its condensing point.
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Solidifying (Freezing) - liquid to solid

  • When the temperature of a liquid decreases to the melting point, the strength of the forces between particles increases and the liquid solidifies to become a solid.
  • For the same material, its melting point is the same as its freezing point.

Jump to other topics

1Energy

2Electricity

3Particle Model of Matter

4Atoms & Radiation

5Forces

5.1Basics of Motion

5.2Forces

5.3Effects of Forces

5.4Pressure

6Waves

7Magnetism

8Astrophysics

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