1. Chemical Properties & Changes

2. Objectives Determine what are chemical properties Describe what happens during a chemical change Compare & contrast physical & chemical properties & changes Identify four possible clues that a chemical change has taken place

3. Important Vocabulary Chemical property Chemical change Precipitate

4. Chemical Properties  Describe how a substance will react  Chemical properties also describe how a substance changes into a new substance  Some substance react very easily combining into compounds  Example: Magnesium  Others rarely combine with other elements  Example: Gold

5. Chemical Properties Rusting: oxygen reacts with some metals forming a new substance known as an oxide Reactivity: the ability of a substance to combine chemically with another substance Flammability: the ability to burn Combustibility: the ability to combust/explode

6. Chemical Changes Are changes in which the identities of the substances change and new substances are formed Words like burn, rot, rust, decompose, ferment, explode and corrode usually indicated a chemical change Processes used to cause a chemical change ◦ Heating ◦ Electrical current ◦ Using a another chemical such as an acid

7. Examples of Chemical Changes

8. Recognizing Chemical Changes There are four possible clues that a chemical change has occurred ◦ A transfer of energy ◦ A color change ◦ Production of gas ◦ Formation of a precipitate

9. Transfer of energy Every chemical change involves a transfer of energy Energy can be given off in the form of heat or light For example: using a battery to turn on a flashlight Energy can also be absorbed For example: cooking food on the stove

10. Color Change Can happen when two liquids are mixed Can happen when a solid and a liquid are mixed

11. Production of Gas Is indicated by the formation of bubbles It can happen when two liquids are combined It can happen when a liquid and a solid are combined

12. Formation of a Precipitate A precipitate is a solid formed out of a liquid mixture This can occur when solutions containing ionic compounds are mixed and an insoluble product is formed

13. Physical Change vs. Chemical Change Physical Change Chemical Change The substances present at the beginning are not present at the end The substances present at the beginning are not present at the end The composition of matter ALWAYS changes The composition of matter ALWAYS changes New substances are made New substances are made It can not be undone It can not be undone Occurs at the molecular level Occurs at the molecular level For example: rusting a nail, cooking an egg, burning wood For example: rusting a nail, cooking an egg, burning wood The substances at the beginning are the same before and after the change The substances at the beginning are the same before and after the change The composition of matter does NOT change The composition of matter does NOT change It can be undone It can be undone For example: melting an ice cube For example: melting an ice cube Includes words like tearing, cutting, carving, melting, boiling, freezing, breaking Includes words like tearing, cutting, carving, melting, boiling, freezing, breaking