Rules for balancing equations Bell Ringer 11-5-09 (Copy in your notebook on NEXT CLEAN PAGE (in notes section). Rules for balancing equations 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).

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

Chapter 6 Section 2 : Describing Chemical Reactions

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

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.

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

Balance Equations with Coefficients Coefficients in front of formulas balance each type of atom. 4NH3 + 5O2 4NO + 6H2O 4 N = 4 N 12 H = 12 H 10 O = 10 O

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

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

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