Physical and Chemical

1. Physical and Chemical Properties and Changes

2. Properties Identify Substances You are identified by your characteristics. You are identified by the colour of your hair and eyes, your weight, and the reaction you have to certain tastes and odours. Characteristics or properties can also identify substances. For example gold has the following properties:

3. Properties of Gold

4. Properties of Water

5. Physical Properties • properties that can be described WITHOUT altering the chemical composition of a substance. • Examples: • colour, • smell, • density, • melting, boiling, or freezing point, • state, • texture, • malleability.

6. Chemical Properties • properties that can be described ONLY by altering the chemical composition of a substance. • Example: • The way elements combine with each other in reactions • Will the substance burn in oxygen • Will the substance react in an acid and produce gas.

7. Physical and Chemical Changes • Physical change • A change in size, shape or state of a substance • No new substance is produced • Can easily reverse • Examples: changing state, dissolving.

8. Physical and Chemical Changes • Chemical change • A change that alters the chemical properties of the substance • A new substance is produced, sometimes smoke can be seen and often there is a change in temperature of the substance • Difficult to reverse. • Example: burning, cooking, rusting

9. How can you tell the difference? • In a physical change, the substances are not altered chemically, but merely changed to another phase (i.e. gas, liquid, solid) or separated or combined. • In a chemical change, the substances are altered chemically and display different physical and chemical properties after the change.

10. How can you tell the difference? There are five indicators of a new substance forming: • Heat or light being given off • A new colour appears • Bubbles – indicating a gas forming • Precipitate – A solid forming in a liquid • The change is difficult to reverse • ..\Links\Potassium_Chlorate_and_Gummy_Bear.flv • ..\Links\reaction_of_LEAD_NITRATE__amp__POTASSIUM_IODIDE_solutions.flv

11. Ice Melts and becomes water Salt is dissolved into water A carrot is cut into many small pieces Yellow and Red Dyes are mixed to form an orange marker ink. How can we reverse some physical changes? Putting the water in a cold environment. Gluing the carrot back together? No, but the carrot pieces are still all carrot pieces! Boiling off the water. Chromatography. Different colours of dyes move up the filter paper allowing them to separate.

12. Is there any way to reverse a chemical change? Hydrogen gas and Oxygen Gas are burned to form water. Some compounds can be broken apart using electricity. This is called electrolysis. 2H2O  O2 + 2 H2 Note: We can test for the different elements using a flaming splint. • Hydrogen: Makes a small popping sound as the hydrogen gas combusts. • Oxygen: Allows the splint to combust faster.

13. Practice Identifying Chemical and Physical Changes Physical Changed from one state to another Can be reversed. Solubility is a physical property Physical Heat or light given off, not easily reversed Chemical Different matter (water and oxygen) at end of decomposition, Chemical

14. Class and Home Work • Read pages 16-19 and 28-30 in your textbook. • Answer questions 1,2 page 30 and • 3, 4, 5, 6, 7, 12, 13 page 41