Question:   What's an easy way to determine if a change in the real world is chemical or physical?

Answer:

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.