Lesson 3 of 7
Changes of state
Goal: Describe changes of state using the particle model.
Heat or cool a substance enough and it changes state. The particles themselves do not change. Only their arrangement and their movement do.
- In the picture, the ice is melting. Water vapour from the air is condensing into drops on the cold glass.
- Evaporating and boiling are different. Evaporation happens at the surface of a liquid, at any temperature. Boiling happens all through the liquid, at its boiling point.
- No particles are made or lost, so the mass stays the same. 10 g of ice melts into 10 g of water.
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Key words in this lesson
Particle A tiny piece of matter, far too small to see
Particle model The idea that everything is made of tiny moving particles
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
Freezing Changing from a liquid to a solid
Evaporating A liquid turning into a gas at its surface, at any temperature
Boiling A liquid turning into a gas all through the liquid
Condensing Changing from a gas to a liquid
Subliming Changing from a solid straight to a gas
Boiling point The temperature at which a liquid boils