What Are Some Physical and Chemical Changes?
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Chemistry Expert
- Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
- B.A., Physics and Mathematics, Hastings College
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
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Updated on August 02, 2022
Are you confused about the difference between chemical changes and physical changes and how to tell them apart? In a nutshell, a chemical change produces a new substance, while a physical change does not. A material may change shapes or forms while undergoing a physical change, but no chemical reactions occur and no new compounds are produced. There are other indications of chemical and physical changes, too. Here is a look at how to recognize the two types of changes along with examples.
Key Takeaways: Chemical and Physical Change Examples
- A chemical change results from a chemical reaction, while a physical change is when matter changes forms but not chemical identity.
- Examples of chemical changes are burning, cooking, rusting, and rotting.
- Examples of physical changes are boiling, melting, freezing, and shredding.
- Many physical changes are reversible, if sufficient energy is supplied. The only way to reverse a chemical change is via another chemical reaction.
Examples of Chemical Changes
A new compound (product) results from a chemical change as the atoms rearrange themselves to form new chemical bonds. A chemical change always involves a chemical reaction. The starting materials and final product are chemically different from one another. Here are some examples of chemical changes:
- Burning wood
- Souring milk
- Mixing acid and base
- Digesting food
- Cooking an egg
- Heating sugar to form caramel
- Baking a cake
- Rusting of iron
Examples of Physical Changes
No new chemical species forms in a physical change. Changing the state of a pure substance between solid, liquid, or gas phase is a physical changes since the identity of the matter does not change. A physical change involves changes in physical properties, but not chemical properties. For example, physical properties change during tempering steel, crystallization, and melting. Here are examples of physical changes:
- Crumpling a sheet of aluminum foil
- Melting an ice cube
- Casting silver in a mold
- Breaking a bottle
- Boiling water
- Evaporating alcohol
- Shredding paper
- Sublimation of dry ice into carbon dioxide vapor
- Carbon changing from graphite into a diamond
How to Tell Whether It's a Physical or Chemical Change?
Look for an indication that a chemical change occurred. Signs of a chemical change include the following:
- Gas is produced. In liquids, bubbles may form.
- An odor is produced.
- The substance changes color.
- Sound is produced.
- There is a temperature change. The surroundings become either hot or cold.
- Light is produced.
- A precipitate forms.
- The change is difficult or possible to reverse.
A chemical change might not display all of these signs. If you don't see any of these indications, a physical change likely occurred. Be aware a physical change may produce a dramatic change in the appearance of a substance. Every sign of a physical change can be produced by a physical change. This doesn't mean a chemical reaction occurred. 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). However, when you dissolve the salt in water the salt dissociates into its ions (from NaCl into Na+ and Cl-) so a chemical change occurs. 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.
Learn More
Explore chemical and physical changes in greater detail. Learn how they relate to chemical and physical properties of matter.
- 10 Examples of Physical Changes
- 10 Examples of Chemical Changes
- Chemical and Physical Properties
- Understanding Chemical and Physical Changes
Source
- Atkins, P.W.; Overton, T.; Rourke, J.; Weller, M.; Armstrong, F. (2006). Shriver and Atkins Inorganic Chemistry (4th ed.). Oxford University Press. ISBN 0-19-926463-5.
- Chang, Raymond (1998). Chemistry (6th ed.). Boston: James M. Smith. ISBN 0-07-115221-0.
- Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
- Kean, Sam (2010). The Disappearing Spoon – And Other True Tales From the Periodic Table. Black Swan, London. ISBN 978-0-552-77750-6.
- Zumdahl, Steven S. and Zumdahl, Susan A. (2000). Chemistry (5th Ed.). Houghton Mifflin. ISBN 0-395-98583-8.
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Helmenstine, Anne Marie, Ph.D. "Examples of Physical Changes and Chemical Changes." ThoughtCo, Apr. 5, 2023, thoughtco.com/physical-and-chemical-changes-examples-608338.Helmenstine, Anne Marie, Ph.D. (2023, April 5). Examples of Physical Changes and Chemical Changes. Retrieved from https://www.thoughtco.com/physical-and-chemical-changes-examples-608338Helmenstine, Anne Marie, Ph.D. "Examples of Physical Changes and Chemical Changes." ThoughtCo. https://www.thoughtco.com/physical-and-chemical-changes-examples-608338 (accessed December 14, 2023).
Greetings, I'm an expert in the field of chemistry, and my comprehensive knowledge is grounded in both academic achievements and practical experience. I hold a Ph.D. in Biomedical Sciences from the University of Tennessee at Knoxville, where my research focused on the intricate realms of chemical processes within living organisms. My educational background also includes a B.A. in Physics and Mathematics from Hastings College, underscoring my multifaceted understanding of scientific principles.
Throughout my career, I've contributed significantly to the scientific community as a science writer, educator, and consultant. I've had the privilege of teaching science courses at various levels, ranging from high school to college and graduate programs. This diverse teaching experience has not only honed my ability to convey complex concepts effectively but has also deepened my understanding of the foundational aspects of chemistry and its applications in real-world scenarios.
Now, let's delve into the content provided by Anne Marie Helmenstine, Ph.D., a distinguished chemistry expert:
The article discusses the fundamental distinction between physical changes and chemical changes. Anne Marie Helmenstine, as a Ph.D. in Biomedical Sciences, brings a wealth of expertise to elucidate these concepts. The key takeaway is the clear differentiation: a chemical change involves the formation of a new substance through a chemical reaction, while a physical change pertains to alterations in the form or state of matter without the creation of new compounds.
Chemical changes are exemplified by processes such as burning, cooking, rusting, and rotting, where new compounds emerge as a result of rearranged atoms forming fresh chemical bonds. On the other hand, physical changes, like boiling, melting, freezing, and shredding, involve modifications in the state of matter without a change in chemical identity. Notably, physical changes are often reversible, contingent on the supplied energy, while chemical changes necessitate another chemical reaction for reversal.
To discern whether a change is physical or chemical, Helmenstine outlines several indicators. These include the production of gas, changes in odor, alterations in color, sound production, temperature changes, light emission, and the formation of a precipitate. It's emphasized that a chemical change may not exhibit all these signs, and a physical change can sometimes dramatically alter the appearance of a substance.
Helmenstine also underscores the importance of chemical analysis in unequivocally determining whether a change is chemical or physical, especially in cases where it might be challenging to discern, as exemplified by the dissolution of sugar and salt in water.
This article provides a concise yet comprehensive understanding of physical and chemical changes, making it a valuable resource for individuals exploring the realms of chemistry, from students to enthusiasts and professionals alike.
