1. SubstancesMixtures

2. SubstancesMixtures ElementsCompoundsHomo- geneous Hetero- geneous

3. Conservation of Mass Unit 1: Measurement & Matter

4. Key Question  What are four possible clues that a chemical change (or reaction) has taken place?  Transfer of energy  Change in color (be careful with this one)  Production of a gas (e.g. H 2, O 2, CO 2 )  Formation of precipitate (ppt)

5. Is this a reaction?  Antacid Tablet…  Gas is produced

6. Is this a reaction?  Adding food coloring to water  This is not a reaction although a color change is observed  A new substance is not created  The substances can be physically separated  Distillation  Evaporation

7. Is this a reaction?  Burning a log  Transfer of energy (chemical to thermal)  Change in color (brown to black/gray)  Production of gas (CO 2 and H 2 O)

8. Key Question  How are the mass of the reactions and the mass of the products of a chemical reaction related?  During any chemical reaction, the mass of the products is always equal to the mass of the reactants.

9. Law of Conservation of Mass  Mass is neither created nor destroyed  Mass of reactants = mass of products

10. So…. Burning a log?  After a log burns, what is left?  ASHES  If the Law of Conservation of Mass is true, where does the mass of the log go? 

11. Combustion Reaction  The mass of the wood and oxygen is converted to carbon dioxide gas and water vapor.  The gases escape into the atmosphere! C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O Wood + oxygen  carbon dioxide + water

12. Practice (Conservation of Mass) Sodium + Chlorine  Sodium Chloride  If 50 grams of sodium react with chlorine to form 126 grams of salt. How many grams of chlorine reacted? 50 g126 g76 g

13. Practice (Conservation of Mass) Water  Hydrogen Gas + Oxygen Gas  If 178.8 g of water is separated into hydrogen and oxygen gas, and the hydrogen gas has a mass of 20.0 g, what is the mass of the oxygen gas produced? 178.8g20.0 g158.8 g

14. Homework  Elements Quiz TOMORROW Wed. 9/24!