Lesson 4 of 7

Energy and changes of state

Goal: Explain what happens to temperature and particles when a substance is heated.

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Heating gives particles more energy. The temperature goes up, except while the substance is changing state.

  • While a pure solid melts, its temperature stays level. The energy is being used to break the particles away from their fixed positions, not to make it hotter.
  • The level part of a heating curve shows the melting point. A second level part, higher up, shows the boiling point.
  • Cooling is the reverse. When a gas condenses or a liquid freezes, its particles lose energy to the surroundings.
A tube of white solid standing in a beaker of hot water over a burner, with a thermometer in the tube
Making a heating curve. Heat a solid gently, read the thermometer every minute, and plot the readings.

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Key words in this lesson

Particle A tiny piece of matter, far too small to see

Solid Has a fixed shape and a fixed volume

Liquid Flows and takes the shape of its container, but has a fixed volume

Gas Spreads out to fill its container, and can be squashed

Melting Changing from a solid to a liquid

Boiling A liquid turning into a gas all through the liquid

Melting point The temperature at which a solid melts

Boiling point The temperature at which a liquid boils

For teachers: AQA 3.5.1, 3.6.3 · Pearson Edexcel 11.2