1. Bell Ringer 11-5-09 (Copy in your notebook on NEXT CLEAN PAGE (in notes section). Rules for balancingequations • You can’t change or add a subscript. • You can only add coefficients (numbers at the beginning of the formula, after plus sign, or after arrow). • There should be the same atoms on both sides. • Both sides should be equal (balanced).

2. ALCOS Objectives: • #1- Identify the steps of the scientific method • #4 State the law of conservation of matter (Balancing Chemical Equations)

3. Chapter 6 Section 2 :Describing Chemical Reactions

4. Chemical Equations • Use chemical formulas and other symbols instead of words to summarize a reaction.

6. Conservation of Mass • The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must be equal to the total mass of the product.

7. A Balanced Chemical Equation Same numbers of each type of atom on each side of the equation. Al + S Al2S3 Not Balanced 2Al + 3S Al2S3Balanced

8. Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom. 4NH3 + 5O24NO + 6H2O 4 N = 4 N 12 H = 12 H 10 O = 10 O

9. Steps in Balancing An Equation Fe3O4 + H2 Fe +H2O Fe:Fe3O4 + H23 Fe +H2O O:Fe3O4 + H2 3 Fe +4H2O H: Fe3O4 + 4 H2 3 Fe +4H2O

10. Endothermic energy – heat energy being absorbed. Ex. Baking something Exothermic energy – heat energy is being released. Ex. Burning something

11. Let’s Try These…Balance these equations • Fe + H2O → Fe3O4 + H2 • C + H → CH4 • Zn + Ag2S → ZnS + Ag • Ag2O → Ag + O2 • Cl2 + NaBr → NaCl + Br2 • K2CO3 + CaCl2 → CaCO3 + KCl • AgNO3 + NaI → AgI + NaNO3