1. Chemical Reactions

2. Atoms Interact in Chemical Reactions Chemical reaction - Produces new substances by changing the arrangement of atoms

3. Atoms and the Periodic Table Periodic Table shows many different things: –Symbols –Names –Other stuff too Number of protons Number of neutrons Atomic Weight 17 Cl Chlorine 35.45

4. Reactants and Products Reactants - the substances present at the beginning of the reaction Products - the substances formed by the chemical reaction

5. Evidence of Chemical Reactions Color change Formation of a precipitate Formation of gas Temperature change

6. Classification of Chemical Reactions Synthesis –A new compound is formed

7. Classification of Chemical Reactions Decomposition –A reactant is broken down to simpler products

8. Classification of Chemical Reactions Combustion –One reactant is oxygen and the other often contains hydrogen and carbon –The products are always carbon dioxide and water

9. Rates of Reaction Rates depend on several factors –Concentration –Surface Area –Temperature

10. Rates of Reaction Rates depend on several factors –Presence of a catalyst Substance that increases the rate of the reaction without changing Enzymes - biological catalysts

11. Chemical Reactions Day 2 Conservation of Mass Balancing Equations

12. Law of Conservation of Mass Again Matter is neither created nor destroyed –Atom in = atom out

13. And your very own Periodic Table To tell which things cannot be created or destroyed

14. Chemical Equations Chemical equations - way to describe a chemical reaction symbolically 2H 2 + O 2  2H 2 O Yield, , shows the direction of the reaction Coefficients tell the number of molecules Subscripts show the number of atoms in the molecule

15. Balancing Chemical Equations Number of atoms in the reactants must equal the number of atoms in the products Balance equations using coefficients

16. So there’s a bit more to it… Some chemical reactions have polyatomic ions – a group of two or more atoms that act as a group –Notation for polyatomics… Na(NO 2 ) 3 1 Na atom 3 N atoms 6 O atoms

17. So how about this one… 2 Na(NO 2 ) 3 2 Na atoms 6 N atoms 12 O atoms

18. NEVER EVER ***NEVER change the subscripts to balance a chemical equation*** Changing subscripts = Changing the substance

19. Practice Activity Balancing chemical equations with the Hardware analogy…again

20. Chemical Reactions Day 3 Energy Transformation Getting hot and Being cool

21. Chemical reactions involve energy changes Chemical reactions involve breaking and making bonds –Breaking bonds costs energy –Making bonds gives energy The energy contained in these bonds is called the bond energy

22. Systems and Surroundings System – red liquidSystem – ice cube Surroundings – airSurroundings – tea, glass, cherry, lemon

23. Exothermic Reactions Products have more bond energy than the reactants Puts the extra energy into the surroundings –Surroundings get hot Thermite reaction videoThermite reaction video – why I can’t demo this type of reaction – and you can’t either!!!

24. Endothermic Reactions Products have less bond energy than the reactants Takes the extra energy out of the surroundings –Surrounding loses heat DON’T SAY GET COLD!!!

25. Don’t try this at home! That’s why we show it done on video by other people with the proper training and equipment!!!

26. Question to consider – Part I Scenario: I light a propane torch, let it run for a bit upside down, then turn it off. Question: Will the tip of the torch be hot or cold?

27. Question to consider – Part II Is the phase change from a liquid to a gas (evaporation) an endothermic or exothermic process? Propane torch demo