1. TOPIC 7 CHEMICAL REACTIONS

2. CHEMICAL CHANGES... What are some ways that you can tell that a chemical reaction has occurred?

3. IN CHEMICAL REACTIONS… A NEW SUBSTANCE IS FORMED EVIDENCE OF THE REACTION MAY INCLUDE: COLOR CHANGE FORMATION OF AN ODOR FORMATION OF A PRECIPITATE FORMATION OF A GAS RELEASE or ABSORPTION OF HEAT/ENERGY

4. WHAT ABOUT THESE SCENARIOS? Smelling a cake in the oven? Watching ice melt? Frying up an egg for breakfast? Bubbles forming when mixing baking soda and vinegar?

5. BREAKING CHEMICAL BONDS Energy is stored in chemical bonds To break bonds, energy must be added When bonds form, energy is released

6. Reactants - CHEMICALS at the BEGINNING of a reaction. Products - NEW MATERIALS produced at the END of a reaction. Ex. wood + oxygen  carbon dioxide + water + E What are the + sign and  for?

7. WRITING REACTIONS WORD equations: silver + bromine  silver bromide CHEMICAL equations: Ag (s) + Br 2 (l )  Ag Br (s )

8. LAW OF CONSERVATION OF MASS In all chemical reactions: The total mass of products is always the same as the total mass of reactants. Reactants mass = Products mass

9. Matter cannot be created or destroyed.

10. Closed System: nothing is allowed to enter or leave the reaction. Open System: matter and energy can enter or leave the reaction (so we have to account for this change ).

11. LAW OF CONSERVATION OF MASS Closed system: Mg (s)+S(s)  MgS(s) 24.3 g 32.1g56.4g Open system: Alka-Seltzer + Water  Product 10g 100g 106 g

12. ENERGY can be placed on either side of a chemical reaction depending on whether it’s being released or absorbed. Endothermic : energy is a reactant or “absorbed” Exothermic : energy is a product or “released”

13. NAME THE REACTANTS AND PRODUCTS IN EACH EQUATION: 1.Ca + Cl 2  CaCl 2 2.H 2 O(l)  H 2 (g) + O 2 (g) 3.2Mg(s) + O 2 (g)  2MgO(s) + light 4.aluminum + fluorine  aluminum fluoride 5.zinc + hydrogen chloride  zinc chloride + hydrogen