2.  Chemical Reaction – Occurs when substances undergo chemical changes to form new substances › Usually you can see a chemical change take place!  Signs a chemical reaction is happening: › 1. Formation of a separate gas (bubbles or fizz) › 2. Formation of a separate solid › 3. See light or feel heat › 4. Color change (like burning)

3.  A physical change keeps the same substance, it just looks different.  A chemical change forms a new substance.  In a chemical reaction there are 2 parts that must be the same on both sides! In the picture to the right, there are the same amounts of Carbon, Hydrogen, and Oxygen on both sides!

4.  Total energy before the reaction is equal to the total energy of the products at the end.  There are two types of reactions in a reaction: › 1. endothermic (heat enters) › 2. exothermic (heat exits)

5.  Exothermic Reaction – The temperature of the surroundings rise because energy is released › Examples:  1. Combustion  2. Fire  3. Hand warmers

6.  Endothermic Reaction – A chemical reaction that needs more heat › Examples:  1. Plastics becoming brittle after being left in the sun  2. Photosynthesis  3. Ice cube melting

8.  Chemical Equations – A representative of a chemical reaction that uses symbols and formulas to show reactants and products › Reactants = left side › Products = right side

9.  Use coefficients to represent the number of units of each substance in a reaction (kind of like the number of ingredients in a recipe)  Use subscripts to represent the number of atoms in a molecule of a particular element

10.  Choosing coefficients becomes easier with practice  At first it is trial and error  A four-step process: › 1. Describe the reaction in words in your head › 2. Write the equation using formulas and symbols if it is not already written that way › 3. Check for balance with numbers under › 4. Add coefficients where needed for balance

11.  P + O 2  P 4 O 10 (Find how many total atoms) 1 P 4 2 O 10  Now use coefficients to balance  4P + 5O 2  P 4 O 10 4 P 4 10 O 10

12.  Al 2 O 3  Al + O 2  Answer: › 2Al 2 O 3  4Al + 3O 2

13.  BaCl 2 + H 2 SO 4  BaSO 4 + HCl  Answer: › BaCl 2 + H 2 SO 4  BaSO 4 + 2HCl

14.  Factors that cause chemical reactions to happen faster: › High temperatures (think about mold) › Large surface area because there are more particles that can react › Concentration level › High pressure › Catalysts