8.1 Describing Chemical Reactions

1. 8.1 Describing Chemical Reactions • Physical indicators of chemrxns • Heat, light, color change, production of gas, formation of a precipitate (solid) • Law of conservation of mass in chemeqns • 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!)

2. 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

3. 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)

4. 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

5. 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