What is the difference between a chemical change and a phyiscal change?

Answer 1

Combining oxygen and hydrogen (separate atoms) to produce water (H2O) is a chemical change involving the electrons that 'glue' atoms together. Freezing or boiling water involves the removal or addition of heat energy to the water molecules but does not change the molecules that remain H2O while experiencing a physical (feels different) change.

Answer 2

In the simplest sense, a chemical change creates a new substance that wasn't there before the reaction.

A physical change just changes the conditions. For example, freezing, boiling, chopping into smaller pieces.