Chemical Changes

Observe signs of chemical reactions: color, gas, temperature, and precipitate

A chemical change creates new substances with different properties. Signs include: color change, gas production (bubbles), temperature change (hot or cold), precipitate formation, and light/sound emission. Unlike physical changes (cutting, melting, dissolving), chemical changes are usually difficult to reverse. Examples: baking soda + vinegar produces carbon dioxide gas; iron + oxygen produces rust.