2 Review: Chemical Changes Chemical Properties Mixtures and solutions are formed through physical changes compounds are formed through chemical changesA compound is a combination of two or more substances that are chemically combinedRelated to internal makeup of substancesDescribe how a substance reacts with other substances to form new substances
3 Signs of a Chemical Change 1. A Color ChangeA chemical reaction in trees causes the leave to change colors
4 Signs of a Chemical Change 2. Something SmellsWhen substance undergo a chemical change, often a new substance that smells different than the original substances is produced.Ex. Rotting meat or sour milk
5 3. The Presence of Bubbles or Frizzing Signs of a Chemical Change3. The Presence of Bubbles or FrizzingThe appearance of bubbles or fuzzing means that a gas is being producedEx. Vinegar and Baking Soda produce Carbon Dioxide
6 Signs of a Chemical Change 4. Light is Given OffWhen a glow stick is bent, a capsule inside breaks, causing the chemicals within the capsule and the stick to react and give off light.
7 5. A Change in Temperature Signs of a Chemical Change5. A Change in TemperatureBurning is a chemical reaction that releases heat energyPhotosynthesis is a chemical reaction that absorbs heat energy from the sun.
8 Signs of a Chemical Change 6. A Precipitate FormsIn some chemical changes, two liquids react and form a new liquid and a solid (precipitate).
9 Signs of a Chemical Change 7. It’s PermanentA chemical change is very difficult or impossible to reverse.Ex. Once you bake a change, you can never change the cake to batter
10 CAUTIONAlthough most of these signs indicate a chemical change, there are exceptions to the rule.Boiling water produces water bubbles but this is a PHYSICAL changeAdding food coloring to water results in a color change, but it’s just a PHYSICAL change.