Changes of State
A change of state occurs when heating or cooling changes the energy of particles, such as melting, boiling or condensing.
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A change of state occurs when heating or cooling changes the energy of particles, such as melting, boiling or condensing.
- Melting: solid to liquid
- Evaporation: liquid to gas
- Sublimation: solid straight to gas
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Changes of State?
Within Chemistry, which covers atoms, bonding, reactions, the periodic table, organic chemistry and the chemistry of everyday life, this topic explains Changes of State. Chemistry links what you can see in the lab to the particles and bonds behind it, so each topic here shows that link in a model.
Check that you can explain Changes of State in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Changes of State helps you explain why substances behave as they do, from cleaning products and food to medicines.
Changes of State in detail
Changes of state happen when energy is added to or removed from a substance. Melting turns a solid into a liquid, boiling or evaporation turns a liquid into a gas, condensation turns a gas into a liquid, freezing turns a liquid into a solid, and sublimation turns a solid straight into a gas, as dry ice does.
During a change of state, the temperature stays constant because the energy is used to overcome the forces between particles rather than to speed them up. These are physical changes and can be reversed, and the mass stays the same. Heating and cooling curves show these flat sections clearly.
How the interactive helps you understand Changes of State
Watch the gas particle model in the interactive. Use any sliders or buttons it offers to change the values and see how the gas particle model responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Changes of State.
Real-life uses and examples
- Link Changes of State to everyday products such as cleaning agents, food and medicines.
- Read a chemical equation or diagram and work out what Changes of State shows.
- Explain Changes of State in an exam by linking the particles involved to what you observe.
Common mistakes to avoid
- Mixing up the names of substances or ions when you describe Changes of State.
- Describing what happens without explaining the particles or bonds involved.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Changes of State
What is Changes of State?
A change of state occurs when heating or cooling changes the energy of particles, such as melting, boiling or condensing.
What are the most important points about Changes of State?
The main points are: Melting: solid to liquid; Evaporation: liquid to gas; Sublimation: solid straight to gas.
Why is Changes of State useful?
Understanding Changes of State helps you explain why substances behave as they do, from cleaning products and food to medicines.
How can I practise Changes of State?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Changes of State?
Related topics in Chemistry include Elements, Compounds and Mixtures, Isotopes and Relative Atomic Mass, Groups and Periods.