Chapter 9

Law of Conservation of Matter Chemical reactions occur when one or more substances are rearranged to form new substances. Ex: 2 Na + H 2 O  2 NaOH + H 2 Indicators of a chemical reaction: Temperature change Color change Production of light Production of gas (bubbles) Formation of a solid (precipitate) Chemical equations are balanced using coefficients to satisfy the Law of Conservation of Matter Coefficients = big numbers (can change) Subscripts = small numbers (do NOT change) Ex: 2 H 2 O

Parts of a Chemical Equation Reactants are the starting substances in a chemical reaction The arrow points away from the reactants Ex: 2 H 2 + O 2  2 H 2 O Products are the substances formed during a chemical reaction The arrow points toward the products Ex: 2 H2 + O2  2 H2O The state of matter can be found on the right side of a compound (aq) = aqueous solution (s) = solid (l) = liquid (g) = gaseous

Steps to Balancing Equations 1.Write formulas for all compounds (sometimes given) (remember your diatomic molecules) 2.Separate reactants and products by a line 3.Count how many atoms of each element are present on the reactant and the product side (element inventory) 4.Add or adjust the coefficients so that element inventory is balanced (subscripts cannot be changed) 5.Reduce coefficients to lowest possible terms (simplify) 6.Check your work

Types of Reactions A chemical reaction that gives off energy is exothermic A chemical reaction that uses energy is endothermic Types of Reactions: 1. Synthesis A + B  AB 2. Decomposition AB  A + B 3. Single Displacement (replacement) A + BX  AX + B 4. Double Displacement (replacement) AX + BY  BX + AY 5. Combustion C 8 H 18 + O 2  CO 2 + H 2 O + ENERGY