8.1 Describing Chemical Reactions Physical indicators of chem rxns Heat, light, color change, production of gas, formation of a precipitate (solid) Law of conservation of mass in chem eqns All reactants/ products identified All reactants = products (use of coefficients) Word Equations Methane + oxygen  carbon dioxide + water Formula Equations (aka Skeleton Equation) CH4 + O2  CO2 + H2O (NOT balanced!)

Step-by-step balancing Balancing equations CH4 + O2  CO2 + H2O C C H H O O Symbols- pg 252 Step-by-step balancing ID reactants & products, write word equation Substitute formulas in for words Balance reactant and product atoms Double check by counting at end again

8.2 Types of Chemical Reactions 5 types of rxns Synthesis- 2 or more substances react to form 1 new substance; 2K+Cl22KCl; (A+XAX; 2 reactants are elements/ compounds make single compound) Decomposition- 1 compound breaks down into 2 or more simpler products; 2H2O H2+O2 ; (AXA+X; compound breaks down into 2 products) Single-replacement- 1 element replaces another element in compound; Zn+H2SO4ZnSO4 +H2 ; (A+BXAX+B; reactants are an element and compound products new compound and other element)

Double-replacement-exchange of +ions; one of following is true-1one product slightly soluble and make precipitate, 2- one product is gas, 3-one product is a molecular compound like water (A+X- + B+Y-A+Y- + B+X- ; reactants 2 ionic compounds products are two new compounds Combustion-reacts with oxygen to product heat and light;[ CxHy + (x+y/4) O2 xCO2 + (y/2)H20;] CH4+2O2CO2+ 2H20

8.3 Activity series of the elements List elements in order of their chem reactivity Predicts whether chem rxn will occur Activity series determined through exp Sometimes no rxn occurs