The only way to know for certain whether a change is chemical or physical is a chemical analysis of the starting and ending materials.
In some cases, it may be hard to tell whether a chemical or physical change occurred. For example, when you dissolve sugar in water , a physical change occurs. The form of the sugar changes, but it remains the same chemically sucrose molecules. In both cases, a white solid dissolves into a clear liquid and in both cases, you can recover the starting material by removing the water, yet the processes are not the same. Explore chemical and physical changes in greater detail.
Learn how they relate to chemical and physical properties of matter. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile. Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance.
Explore the relationships between ideas about physical and chemical change in the Concept Development Maps - States of Matter, Chemical Reactions. When teaching about physical and chemical changes it is important to allow students to see the classification as a continuum.
They should be able to observe a number of changes and formulate their views on the kind of change and problems with the classification process. Students should come to see that chemical reactions produce new chemicals distinct from the starting materials but that chemical processes can be reversed. Examining examples of reversible chemical reactions and considering why it is difficult to reverse many chemical changes can be very useful. Promote reflection on and clarification of existing ideas The following activities are intended to get students identifying and then refining their ideas about physical and chemical change.
It is important for students to observe a number of changes and to record their opinions on what is happening. They could record this in a booklet where they write about and draw results and observations. They should be encouraged to formulate and record hypotheses about what is happening with the knowledge that their opinions will not be assessed at this stage. For an example of this technique see: Using logbooks in year 10 electricity.
This can help bring out their existing ideas and help them challenge and extend their existing beliefs. Practise using and build the perceived usefulness of a scientific model or idea It is important that examples of changes are not confined to only the materials and chemicals students are exposed to in the classroom.
As a homework activity students could be asked to collect examples of changes they see around them and classify these on their scale of physical and chemical changes. Some examples they may collect are combustion of fuels, cooking and processes such as digestion, respiration and photosynthesis. Communicating their ideas to others can help students clarify and consolidate new and existing ideas about changes. Practise using and build the perceived usefulness of a scientific model or idea Science is an area where deeper meaning for a number of key ideas is built gradually by using them in a range of situations and stressing how the same idea helps make sense of many situations.
Both elements and compounds a key idea at the macro level and atoms and molecules which involve the same thinking at the micro level are examples of this, but their usefulness can be developed by showing among many other things how they can help make sense of physical versus chemical changes. These ideas may be introduced here, or referred back to if they have been introduced earlier.
Writing chemical equations in word and symbolic form can be introduced as a useful way of describing some of the changes students have seen and also to show the advantages of chemical symbols in keeping track of the elements or atoms in ways that words do not. If the exact chemical formulae cannot be written as is the case with most biochemicals a drastic simplification can still be useful.
For example wood is mostly cellulose, a polymer of glucose, and a representation such as C 6 H 10 O 5 n can be used to track changes in processes like combustion. Models and diagrams can help here. For example, most schools have molecular modelling kits which can be adapted to show how molecules have altered and atoms have rearranged as a result of changes. As a result, brass represents a physical change instead of a chemical change.
Remember that a physical change is a change in properties such as texture, shape, or state, while a chemical change represents the formation of a new substance after atoms are rearranged in a chemical reaction. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Matter makes up all visible objects in the universe, and it can be neither created nor destroyed. Bioluminescence is light emitted by living things through chemical reactions in their bodies.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Oxidized Copper Lion The process of rusting, or oxidization, exemplifies a chemical reaction.
Photograph by Paul Damien. Here are the basic definitions of chemical and physical changes:. But when it undergoes a physical change, it only needs to return to its original state of matter. Chemical changes occur all around you in everyday life. Whenever a chemical reaction occurs, the chemical properties of the original substance change to create an entirely new substance. Some examples of chemical changes include:. Most of these changes cannot be undone after a chemical reaction.
Physical changes involve an object or substance changing shape or state of matter.
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