1. Introduction to Chemical Equations 3221.3.2, 3221.3.1

2. Chemical Equation Represents, with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reactions (NH 4 ) 2 Cr 2 O 7 (s)  N 2 (g) + Cr 2 O 3 (s) + 4H 2 O (g)

3. Indications of a chemical reaction 1.Evolution of energy as heat and light. 2.Production of a gas 3.Formation of a precipitate precipitate: a solid that is produced as a result of a chemical reaction in solution and that separates from the solution 4. Color change

4. Characteristics of Chemical Equations 1.The equations must represent known facts. 2.The equation must contain the correct formulas for the reactants and products. 3.The law of conservation of mass must be satisfied. -coefficient: small whole number that appears in front of a formula in a chemical equation

5. Word Equations Word equation: equation in which the reactants and products in a chemical reaction are represented by words – Only qualitative (descriptive) meaning: does not give the quantities of reactants used or products formed – The arrow, , is read as react to yield or yield (also produce or form) Methane + oxygen  carbon dioxide + water

6. Formula Equations Represents the reactants and products of a chemical reaction by their symbols or formulas CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O (g)

7. Additional Symbols in Equations (s) means the substance is in a solid state (g) means the substance is in a gaseous state (l) means the substance is in a liquid state (aq) means the substance has been dissolved in an aqueous solution (which is to say, water) → means "yields" and is used to indicate the result of the reaction. ↔ means that the reaction is reversible ↑ indicates a change of state (into a gas) ↓ indicates a precipitate formed by a reaction ∆ (over the reaction arrow) indicates the application of heat to the reactants

8. Significance of a Chemical Equation 1.The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products 2.The relative masses of reactants and products of a chemical reaction can be determined from the reactions coefficients 3.The revers for a chemical reaction has the same relative amounts of substances as the forward reaction

9. Balancing a Chemical Equation 1.Identify the atoms in the chemical equation. 2.Count the numbers of each type of atom in the reactants and in the products. 3.Balance the different types of atoms one at a time 4.First balance the atoms of elements that are combined and that only appear once on each side of the equation 5.Balance polyatomic ions that appear on both sides of the equation as single units 6.Balance H and O atoms after atoms of all other elements have been balanced 7.Count all atoms, to ensure the equation is balanced.