Changes of State
Science: KS3, topic 3.5.2
Changes of State
Changes of state are examples of a physical reaction.
Changes of state
- A change of state is a physical reaction.
- The mass at the start and end does not change.
- Changes of state happen when there is an increase or decrease in energy.
- A change of state happens between solids, liquids, and gases.
Internal energy
- The energy a substance has is known as its internal energy.
- Gases have the most internal energy.
- Solids have the least internal energy.
- If you heat a substance, it will increase the amount of internal energy.
- If you cool a substance it will decrease the amount of internal energy.
Examples of changes of state
- Melting: Solids to Liquids → increase in internal energy.
- Freezing: Liquids to Solids → decrease in internal energy.
- Evaporation: Liquids to Gases → increase in internal energy.
Condensation and sublimation
- Condensation: Gases to Liquids → decrease in internal energy.
- Sublimation: Solids to Gases → increase in internal energy.
Reversible reactions
- Physical reactions are reversible.
- A reversible physical reaction is when there is a change of state.
- The change of state changes back again.
Shower room condensation
- Water will evaporate in a hot shower room.
- The water vapour will then turn back to liquid on a cold mirror.
- The change back to liquid is condensation.
Test yourself on Changes of State
Which state has the most internal energy?
Which of these are true of physical reactions?
Which list puts the three states of matter in order from least to most internal energy?