Question: What's an easy way to determine if a change in the real world is chemical or physical?
In everyday living, it's typically true that if you destroy something entirely without any possibility of it ever returning to the way it was, it's undergone a chemical change. For example, if you shatter a window, you can imagine melting the window down and making a new one from the glass fragments. However, if your muffler rusts, it's not possible to unrust it.
This rule doesn't always work, but it does a surprisingly good job for most things.