When atoms are mixed, their properties do not change. But when they are chemically combined with other atoms, they get a completely new set of properties.

• We say mixing is a physical change. Physical changes change the way something looks or how it is arranged, but do not change what it is. Dissolving, freezing, and boiling are all physical changes. When water freezes it becomes ice. Ice is H₂O just like liquid water, so the substance^* did not change in the freezing process. (28.8K) (56.7K) (download)

• A chemical change produces a new substance with different properties from the original substances. Chemical bonds are broken and or made during this process. A flame or the production of a gas are two signals that a chemical reaction has taken place. When hydrogen [H₂] burns, water [H₂O] is formed. H₂ and H₂O are different substances that don't look or act alike. (28.8K) (56.7K) (download)