1. Chapter 6-Chemical Reactions Making new “stuff” from old “stuff” Can happen two ways: 1. Bond single elements together to make compounds 2. Rearrange elements already in compounds (breaks old bonds and forms new ones) New “stuff” usually has new characteristics or properties O2O2 H2H2 What does H 2 & O 2 gas create?

2. Evidence of Chemical Change We see reactions taking place when something: Burns Rusts Rots Bubbles or fizzes Examples combining vinegar & baking soda burning a piece of wood cooking food

3. Chemical Changes are Described using Chemical Equations A chemical “story” of a reaction taking place Equations can be made up of several different elements and compounds along with numbers and symbols (+,-, ,=) Examples: 2H 2 + O 2  2H 2 O Every equation has two sides: 1.Reactants (left side) 2.Products (right side)

4. Other info about Chemical Equations 2H 2 + O 2 2H 2 O  (Reactants) (Products) ( Yields, Makes,Turns into ) Chemical Formulas Chemical Formula Subscripts Coefficient Subscript

5. Law of Conservation of Mass In a chemical reaction, atoms are not created or destroyed All atoms present in the reactants should also be in the products (what you start with you must end up with) Law of Conservation of Mass - YouTube

6. Chemical Reactions are very much like recipes used for baking For Example…. 2 cups (260 grams) all purpose flourflour 1 1/4 teaspoons baking sodabaking soda 1/4 teaspoon salt 3/4 cup (170 grams) unsalted butter, room temperaturebutter 2/3 cup (130 grams) granulated white sugar 2/3 cup (140 grams) firmly packed light brown sugarsugar 1 large eggegg 1 large egg yolk 1 1/2 teaspoons pure vanilla extractvanilla 1 1/4 cups (210 grams) chocolate chunks (can use chocolate chips) WHAT DO YOU GET? HOW MANY WILL IT MAKE?

7. NO. You get this you fool…..

8. Does This Make Sense? Na + Cl  H 2 O……why not? Na + Cl  100 NaCl…..why not? When things don’t make sense you need to Balance Equations

9. Balancing Equations -method used to describe reactions accurately All reactions should have Same type of elements on both sides Same amount of elements on both sides Steps to balance an equation: 1. Make a list of the elements on both sides 2. Count the reactant side and get a total 3. Count the product side and get a total 4.Use coefficients on either side to balance. NEVER CHANGE SUBSCRIPT NUMBERS 5. Continue on both sides until everything is equal Balancing Equations Practice

10. Practice 1. Mg + O 2  MgO

11. Practice continued 2. NaCl  Na + Cl 2

12. Keep going…. 3. CH 4 + O 2  CO 2 + H 2 O

13. Chemical Reactions can be put into Three categories 1.Synthesis (creating) 2.Decomposition (separating) 3.Displacement/Replacement (switching) 1. Synthesis- two or more things put together(bonded) to make something new Ex. A + B  AB Hydrogen (H) + Oxygen (O)  water (H 2 O)

14. 2. Decomposition- opposite of synthesis; things are broken apart Ex. AB  A + B Water  Hydrogen and Oxygen 3. Displacement (replacement) - something is switched around Ex. A + BC  AC + B = single (1 thing switched) AB + CD  AD + CB = double (2 things switched)

15. This is what it looks like

16. Practice (they are NOT balanced- don’t worry about that) Are these reactions synthesis, decomposition, or single/double replacement reactions? (1) Hg + O 2 ---> HgO (2) Fe + CuSO 4 ---> FeSO 2 + Cu (3) HCl + NaOH ---> NaCl + H 2 O (4) HNO 3 ---> H+ + NO 3 -

17. Energy and Chemical Reactions - most reactions either use energy to start or give off energy at the end Exothermic Reaction exo=outside therm=heat A chemical reaction in which heat energy is released (this makes things get warmer). Ex. burning Endothermic Reaction endo=inside therm=heat A chemical reaction in which energy is absorbed (this makes thing get colder). Ex. Ice pack