Examples of Physical Changes and Chemical Changes

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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.

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 also other indications of chemical and physical changes, such as odor and sound. Here is a look at how to recognize the two types of changes, along with telltale indications and common examples of each.

Key Takeaways

• 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, but 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 a 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 the solid, liquid, or gas phase is a physical change 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 Physical and Chemical Changes Apart

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. 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 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 the chemical and physical properties of matter with these additional resources.

• More Examples of Physical Changes
• More Examples of Chemical Changes
• Chemical and Physical Properties
• Understanding Chemical and Physical Changes