* Physical Change: A change in the form or appearance of a substance, but not its chemical composition.

* The glass is still made of the same chemical compounds (silicon dioxide, etc.) even after it breaks.

* The change is primarily in the shape and size of the glass.

* Chemical Change: A change where new substances with different chemical properties are formed.

* There is no new substance created when glass breaks.

Think of it this way: You can potentially put the pieces of broken glass back together to form the original shape. This wouldn't be possible if a chemical change had occurred.