A chemical change is a change in the form of matter resulting from a chemical reaction. Either one substance breaks down into other substances or else two or more materials combine and form new products. In contrast, a physical change occurs when a substance changes its form, but not its chemical identity. Here are examples of chemical changes and a look at how to distinguish them from physical changes.
- In a chemical change, the starting and ending materials have a different chemical composition.
- Examples of chemical changes include cooking, combustion, digestion, and rotting. All involve chemical reactions.
- While many physical changes are reversible, the only way to reverse a chemical change is via a chemical reaction. Even then, some chemical changes are not reversible.
Examples of Chemical Change in Everyday Life
Chemical changes occur whenever a chemical reaction occurs. This includes reactions in the lab, but chemical changes are common in the world around us, too. Here are examples of chemical changes in everyday life.
- Burning any fuel, such as wood or propane
- Digesting food
- Baking a cake or cookies
- Electroplating a metal
- Using a battery
- Rotting food
- Exploding fireworks
- Rusting metal
- Ripening food
- Souring milk
- Photosynthesis
- Mixing vinegar and baking soda (an acid and a base)
- Browning meat
- Bleaching a stain
- Dyeing hair
- Leaves changing colors
How to Recognize a Chemical Change
A chemical change involves a chemical reaction, so matter has a different composition before and after the change. Since you can’t see matter at a molecular level, recognizing a chemical change means looking for evidence of a reaction. Here are some indications of a chemical change:
- Changing color
- Producing gas
- Changing temperature
- Producing odor
- Changing chemical properties (e.g., oxidation state, flammability)
- Forming a precipitate
- Producing sound
- Producing light
- Difficult or impossible to reverse
Note that some of these signs also accompany physical changes. For example, phase changes affect temperature. Crushing a can produces a sound. But, a chemical change typically involves several signs, while a physical change only produces one or two.
Is a Chemical Change Reversible?
Irreversibility is often cited as the key indicator of a chemical change. However, some chemical changes are reversible via another chemical reaction. For example, combining hydrogen and oxygen and forming water is a chemical change that you can reverse by a chemical reaction. Most chemical changes are irreversible. If you burn wood, no chemical change returns ashes back into their earlier form. If you cook an egg, you can’t un-cook it. But, some physical changes are irreversible, too. Shredding paper is a physical change, but you can’t really put the pieces back together again.
Types of Chemical Changes
Chemical changes are classified as inorganic chemical changes, organic chemical changes, and biochemical chemical changes.
Inorganic Chemical Changes
Inorganic chemical changes involve inorganic compounds. Mostly, these are chemical reaction that don’t involve carbon. Sometimes these reactions occur in a lab, but other times they appear in the world around us. Here are some examples of inorganic chemical changes.
- Rusting metal
- Tarnishing silver
- Chemical weathering of rocks
- Acid-base reactions
- Redox reactions
- Electrochemical cell reactions
- Haber process of making ammonia (NH3)
- Exploding fireworks
Organic Chemical Changes
Organic chemical changes are chemical reactions involving organic compounds. These are substances that contain both carbon and hydrogen. Here are some examples of organic chemical changes.
- Making gasoline from petroleum
- Making nylon and most other polymers
- Synthesizing aspirin
- Cooking
- Cleaning with soaps and detergents
Biochemical Chemical Changes
Technically, biochemical chemical changes are a class of organic chemical changes. The difference is that biochemical changes occur in living organisms. Here are examples of biochemical chemical changes:
- Digestion
- Photosynthesis
- Cellular respiration
- Leaves changing colors
- Tanning
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.
- Vogel, A.I.; Tatchell, A.R.; Furnis, B.S.; Hannaford, A.J.; Smith, P.W.G. (1996). Vogel’s Textbook of Practical Organic Chemistry (5th ed.). Prentice Hall. ISBN 0-582-46236-3.
- Zumdahl, Steven S.; Zumdahl, Susan A. (2000). Chemistry (5th ed.). Houghton Mifflin. ISBN 0-395-98583-8.