1. Chemical Reactions and Equations CLASS NOTES Wed. Sept. 29th/Thurs. Sept. 30, 2010

2. Review from last class What types of changes can occur as a result of chemical reactions? Can you give an example? Physical changes! Chemical changes!

3. What is involved in a chemical reaction? There are two parts to a chemical reaction: Reactants and Products Reactants are those substances you begin with Products are the substances formed by the reactionReactant1 + reactant2  products For example: sodium (Na) + chlorine (Cl₂)  sodium chloride (NaCl)

4. Chemical equations Chemical reactions are written using equations, with reactants on one side and products on the other: Word equations! e.g. sodium + chlorine  sodium chloride carbon + oxygen  carbon dioxidecalcium + oxygen  calcium oxide Usually written with chemical formulas (symbols): Ex.Na + Cl NaClC + O₂  CO₂Ca+ O  CaO

5. Chemical equations continued… The numbers of atoms on each side of the chemical equation is equal to the other side: Reactant1 + reactant 2  product  is the same as equals, or produces

6. Endothermic and Exothermic Reactions In a chemical reaction, some bonds in the reactants break and new bonds form in the products Breaking and creating bonds requires energy Two types of chemical reactions: Absorbs energy = endothermic (energy in = ENtrance) Releases energy = exothermic (energy EXits)