1. Chemical Reactions

10. Balancing Chemical Equations

18. Example H 2 + H 2 O O 2  Make a table to keep track of where you are at

19. Example H 2 + H 2 O O 2  Need twice as much O in the product R P H O 2 2 2 1

20. Example H 2 + H 2 O O 2  Changes the O R P H O 2 2 2 1 2

21. Example H 2 + H 2 O O 2  Also changes the H R P H O 2 2 2 1 2 2

22. Example H 2 + H 2 O O 2  Need twice as much H in the reactant R P H O 2 2 2 1 2 2 4

23. Example H 2 + H 2 O O 2  Recount R P H O 2 2 2 1 2 2 4 2

24. Example H 2 + H 2 O O 2  The equation is balanced, has the same number of each kind of atom on both sides R P H O 2 2 2 1 2 2 4 2 4

25. Example H 2 + H 2 O O 2  This is the answer R P H O 2 2 2 1 2 2 4 2 4 Not this

27. Evidence of Reactions Looking for the clues

28. Evidence of Reactions Just because the evidence is there DOES NOT mean a chemical reaction is taking place Have to look at everything that is going on

29. Evidence of Reactions 1. Formation of a gas Observations: Bubbles Smoke Odor/fumes

30. Evidence of Reactions 2. Change in color Be Careful! Some changes in color are physical changes!

31. Evidence of Reactions 3. Formation of a solid (precipitate) Observations: “ Cloudy” “ Foggy” Solid at bottom

32. Evidence of Reactions 4. Change in heat or light energy Observations: gets warm/hot/cold spark or explosion glows

33. Exothermic Reactions: Give off energy as heat or light WHY?? Because energy stored in chemical BONDS In EXOthermic reactions there is MORE energy stored in bonds of reactants than needed to form products! So.. there is left over energy!

34. Endothermic Reactions: Absorb energy as heat or light WHY?? Because the energy stored in the bonds of the reactants is NOT ENOUGH to hold together the products. MORE ENERGY IS NEEDED!

35. Evidence of Reactions Summary 1. Formation of a gas 2. Change in color 3. Formation of a solid (precipitate) 4. Change in heat or light energy

36. Types of Reactions Predicting the Products

55. Chapter 7 Summary