The chemical equation is a written representation of a chemical reaction showing the reactants and products using chemical formulas and symbols. It must obey the laws of conservation of mass and matter, meaning the same number and type of atoms are on both sides and the total mass is conserved. Examples are provided to demonstrate balancing chemical equations so the number of each type of atom is equal on both sides.

1. The Chemical Equation J. Hervol

2. The Chemical Equation The chemical equation is a written representation of what happens during a chemical reaction. It includes chemical formulas and symbols . J. Hervol

3. Parts of the Chemical Equation 2 H 2 (g) + O 2 (g)  2 H 2 O(g) Reactants Products “ Yields” Coefficient Physical State Symbols (g) = gas, (l) = liquid (s) = solid, (aq) = aqueous J. Hervol

4. Representation 2 H 2 (g) + O 2 (g)  2 H 2 O(g) 2 molecules + 1 molecule = 2 molecules of hydrogen of oxygen of water OR 2 moles + 1 mole = 2 moles of hydrogen of oxygen of water OR J. Hervol 4.04 g H 2 + 32.00 g O 2 = 36.04 g H 2 O

5. Law of Conservation of Mass Notice that the total number of grams of the product produced was equal to the total number of grams of reactants used. This is called the Law of Conservation of Mass – In a chemical reaction, the total mass of the reactants must equal the total mass of the products. J. Hervol

6. Law of Conservation of Matter In addition to the masses being equal, the number of times each atom appears in the reactant and product side must be equal. This is called the Law of Conservation of Matter – In a chemical equation, matter (atoms) can not be created nor destroyed. J. Hervol

7. Example: 2 H 2 (g) + O 2 (g)  2 H 2 O(g) Reactants : Products : J. Hervol H - O - H - O - 4 2 4 2

8. Balance this unbalanced equation: Zn + HCl  ZnCl 2 + H 2 J. Hervol Cl H Zn Reactants 1 1 1 2 Cl 2 H 1 Zn Products 2 X X 2 2

9. Balance this unbalanced equation: Al 2 O 3 + Pb  PbO + Al J. Hervol Pb O Al Reactants 1 3 2 1 Pb O 1 Al Products 1 2 X 2 3 X 3 X 3 X 3 3

10. Reactions containing polyatomic ions: Hint: Polyatomic ions can be balanced as a group as long as the groups remains on the product side. J. Hervol

11. Balance this unbalanced equation: AgNO 3 + BaCl 2  AgCl +Ba(NO 3 ) 2 J. Hervol Ba NO 3 Ag Reactants 1 1 1 1 Ba NO 3 1 Ag Products 2 Cl Cl 2 1 2 X 2 X 2 2 X 2 X 2