Chopping a banana. Since cutting a banana only changes its appearance, a new substance is NOT formed. That makes this an example of a physical change.
Chemical changes make new substances
Anytime a new substance is made, a chemical change takes place. Usually two or more materials are combined and a new substance is formed. A chemical change can produce amazing explosions, like fireworks. Some chemical changes are a little more difficult to spot, like when a nail rusts.
If you notice bubbles being formed, or a change in color or temperature, there is a good chance a chemical change has taken place, but not always. Scientists can determine if a chemical change has occurred by asking this question: Was the substance formed present before? If the answer is no, then it is a chemical change.
Since chemical changes make new substances, most of them cannot easily be undone. For example, when you burn wood, you can’t really turn the gases back into a log very easily.