States of matter: Basics
Check out this PhET simulation on states of matter to explore how the particles behave during changes of state.
Physical and chemical changes
Matter is dynamic in nature. Explore how it undergoes physical and chemical changes, including transformations between different states such as melting, freezing, and evaporating.
Physical change
A physical change is when the substance changes its physical appearance or state without affecting its chemical identity. Examples of physical changes include:
- the grating of a piece of cheese
- the boiling of water
- sugar dissolving in water.
Change of state
When a substance converts from one physical state to another, this is known as a change of state. Let's look at changes of state using water as an example.
Water is one of the few substances that can exist in all three states: solid ice, liquid water, and gaseous steam or vapour. The process of state changes have different names depending on which states are involved.
- Melting is when a solid changes to liquid.
- Freezing is when a liquid changes to solid.
- Condensation is when a gas changes to liquid.
- Vaporisation is when a liquid changes to gas.
- Deposition is when a gas changes to solid.
- Sublimation is when a solid changes to gas.
Changing states of matter image, by RMIT, licensed under CC BY-NC 4.0
Chemical change
A chemical change is when a substance changes its chemical identity or composition. It involves the formation of new substances that have different properties compared to the original substance. Examples of chemical changes include:
- the rusting of iron objects when exposed to moist air for a long period of time
- sugar heated in a saucepan to make caramel
- the burning of potassium in water
- milk turning sour.
Extracting compounds from plant material
Tea tree and calytrix extract for medicine
The Yaegl Peoples of the Coffs Harbour region of New South Wales heated Melaleuca spp. (tea tree) leaves, which contain oils with medicinal properties. By applying heat, the liquid oil can be extracted into a vapour or gas. This vapour is then breathed in to treat respiratory conditions.
The Ngarrindjeri Peoples of the Murray River region in South Australia used steam released from wet plant material, and the Anindilyakwa Peoples of Groote Eylandt and Bickerton Island in the Gulf of Carpentaria extracted vapours from Calytrix (fringe myrtle) to relieve head colds.
Melaleuca leaves image, by Geoff Derrin via Wikimedia Commons, licensed under CC BY-SA 4.0
Eucalyptus extract to make dyes
Stephanie Beaupark is a Ngugi researcher and Associate Lecturer in the School of Geography and Sustainable Communities at the University of Wollongong. Her work involves extracting Australian Indigenous dyes from eucalyptus leaves to understand how the colours of the dyes change with the seasons. These coloured substances are released when the leaves are boiled.
Stephanie’s research helps us understand the weather cycles in the Sydney Basin, and connect chemistry with Indigenous ways of being and forming new knowledges.
Eucalyptus leaves image, by PublicDomainPictures via Pixabay
- Australian Curriculum, Assessment and Reporting Authority (ACARA) (2016) Science Teacher Background Information AC9S5U04_E6 | V9 Australian Curriculum, Australian Curriculum, Assessment and Reporting Authority, accessed 20 June 2025. https://v9.australiancurriculum.edu.au/support-resources/background-information/science_teacher_background_information_AC9S5U04_E6
- Feakins J (2024) 'Stephanie Beaupark Sees Chemistry Through an Indigenous Lens', ACS Central Science, 10(12):2178–2181, doi:10.1021/acscentsci.4c02023
- Glyde I (9 February 2023) 'Ngugi scientist and artist receives prestigious Australian Academy of Science Award', University of Wollongong Australia, accessed 20 June 2025. https://www.uow.edu.au/media/2023/ngugi-scientist-and-artist-receives-prestigious-australian-academy-of-science-award-.php
Your turn – physical and chemical changes
Test yourself on your understanding of physical and chemical changes.
