A physical change alters the form of matter, but not its chemical composition. In other words, physical changes affect physical properties of a substance, but not its chemical properties. The color, size, and shape of a substance may change, but no chemical reaction occurs and no new products form. Here are physical change examples, along with a look at how to tell a physical change from a chemical change.
How to Identify a Physical Change
Physical changes involve changes in physical properties. Certain processes result in physical changes:
- Phase transitions: Melting, freezing, evaporation, and sublimation are all physical changes.
- Heating and cooling: Temperature changes can result in phase transitions. Be careful, though, because sometimes adding heat supplies energy for a chemical reaction to occur.
- Mixtures: In chemistry, components of a mixture retain their chemical identity. Use caution, because the general usage of the word mixture includes some chemical reactions! For example, you bake a cake by “mixing” ingredients, but this results in a chemical reaction.
- Crystallization: Crystallization orders the arrangement of atoms and molecules, but does not change their identity.
- Allotrope changes: Again, the arrangement of molecules changes, but not the chemical identity. For example, graphite and diamond are both allotropes of elemental carbon.
- Magnetization: Magnetizing and de-magnetizing iron or another substance is a physical change.
- Tempering: Tempering steel involves heating and hammering steel. While its hardness and flexibility change, its chemical composition does not.
Some physical changes are reversible, but others are not. However, reversibility usually indicates a physical change.
Physical Change Examples
Remember, in a physical change the appearance of matter changes, but its chemical composition remains the same. The size, shape, state, or color of matter may change. Here are several examples of physical changes:
- Melting an ice cube
- Crushing a can
- Shredding paper
- Boiling water
- Mixing sand and water
- Mixing sand and salt
- Mixing oil and water
- Breaking glass
- Cracking an egg
- Freezing water to make ice
- Dissolving sugar in water
- Melting sulfur (This causes a color change, even though the element remains the same. Many elements change color when they change phase.)
- Filling a bowl with different colored candies
- Sublimation of dry ice into carbon dioxide gas
- Mixing flour, salt, and sugar
- Chopping an apple
- Breaking a rock
- Evaporating liquid nitrogen
- Mixing blue and yellow marbles
- Mixing paint colors
- Crumpling a paper bag
- Melting wax
- Origami (folding paper)
- Making shapes from clay
- Popping a balloon
- Slicing bread
- Tempering steel
- Melting a crayon
- Cutting your hair
Note that some changes are not reversible, such as cracking an egg, slicing bread, shredding paper, or breaking a rock.
Examples That Are Not Physical Changes
These are examples of chemical changes, not physical changes:
- Combining baking soda and vinegar
- Mixing any acid and base
- Burning wood
- Digestion
- Cooking
- Rust, verdigris, tarnish or any other oxidation
Chemical vs Physical Change
Often, the easiest way to identify a physical change is to rule out the presence of a physical change. Basically, if you don’t see these signs of a chemical reaction, it’s likely a physical change occurred:
- Bubbling or producing gas
- Releasing an odor
- Formation of a precipitate
- Inability to reverse the change
- Releasing or absorbing heat (temperature change)
- Changing color
- Forming a new chemical
- Changing chemical properties (oxidation state, flammability, etc.)
If a new chemical forms, it’s a sure sign of a chemical change. However, in some physical changes, a substance may change color or temperature or the change may be irreversible. These are indicators of both chemical and physical changes.
References
- Burgin, Mark (2016). Theory Of Knowledge: Structures And Processes. World Scientific. ISBN 9789814522694.
- Meyers, Robert A. (2001). Encyclopedia of Physical Science and Technology (3rd ed.). Academic Press. ISBN 978-0-12-227410-7.
- Zumdahl, Steven S.; Zumdahl, Susan A. (2000). Chemistry (5th ed.). Houghton Mifflin. ISBN 0-395-98583-8.