1. Balancing Chemical Equations

2. Recall The law of conservation of mass states that mass cannot be created nor destroyed in a chemical reaction. Chemical equations are written to show all of the reactants and products in a chemical reaction. To be sure the equation does not violate the conservation of mass, we must balance it.

3. Balancing Chemical Equations Consider the following skeleton equation: Let’s look at the atoms of each element present: Where did the atom of oxygen go? Nowhere! We just need to balance the equation. H 2 + O 2 H2OH2O # ReactantsAtom# Products H 22 O 21

4. To balance an equation we simply add coefficients to our equation so that our RAP table is correct: Our balanced chemical equation is: H 2 + O 2 H2OH2O # ReactantsAtom# Products H 22 O 21 2 2 4 4 2 H 2 + O 2 H2OH2O 2 2

5. Balancing Tips 1. Balance elements of complicated formulas first. 2. Never change a subscript in a compound, only add coefficients. 3. Hydrogen & oxygen will appear very frequently so balance hydrogen second last and oxygen last. 4. You MAY be able to treat polyatomic ions as a group instead of separating them.

6. Example #2 Balance the chemical equation below: N 2 + H 2 NH 3 # RAtom# P N 21 H 23 6 2 2 3 6

7. Example #3 Balance the chemical equation below: Na + HClH 2 + NaCl # RAtom# P Na 11 Cl 11 H 12 2 2 2 2 2 2 2 2

8. Example #4 Given the word equation below, determine the balanced chemical equation. Copper (I) Oxide + Carbon  Copper + Carbon dioxide

9. Cu 2 O + C Cu CO 2 + # RAtom# P Cu 21 C 11 O 12 2 2 4 4 2 2 4

10. Example #5 Given the word equation below, determine the balanced chemical equation. Silver Nitrate + Calcium Chloride  Silver Chloride + Calcium Nitrate

11. AgNO 3 + CaCl 2 AgCl Ca(NO 3 ) 2 + # RAtom# P NO 3 12 Ag 11 Ca 11 2 2 2 Cl 2 2 2 1 2

12. Homework P.236 #3, 5-7