Jean Lee Lin Chem 2 Chapter 6 & 71 Writing Chemical Reactions (to save words) –Chemical Formulas –Specify physical state (g), (l), (s), and (aq) HCl(l) ≠ HCl(aq) pure substance ≠ mixture –Reactant and Product –Experimental conditions on arrows e.g. UV, catalyst, “ ᅀ ” ( heat), H + etc. –A dangerous example A (s) + B (l) → C(g) + D (g) + heat Fig. 6.5 p.157, Exothermic or endothermic? - Four Signs of chem. Rx. - p.154

Jean Lee Lin Chem 2 Chapter 6 & 72 Recall Dalton’s atomic theory (p.88) Atoms are neither created or destroyed in a chem. Rx. Balancing chem. Rx. –Do odd atoms first, then hydrogen, and oxygen the last –Need smallest integers for coefficients –e.g. Combustion of octane (hydrocarbons in gasoline),or carbohydrates : ? C 8 H 18 (l) + ? O 2(g) → ? CO 2 (g) + ? H 2 O (g) + heat Q: why O 2(g) and not O (g) ? HW#14,16,19,20,23,27,29,33,38,39

Jean Lee Lin Chem 2 Chapter 6 & 73 Chemical Reaction Types I. Decomposition (p.197) AB  A + B A, B are either compound or element (NOT ions) e.g. Electrolysis: 2 NaCl (l)  2 Na (s) + Cl 2(g) II. Synthesis (or combination) A + B  AB Reverse decomposition e.g. polymerization for PE, PP (plastics)

Jean Lee Lin Chem 2 Chapter 6 & 74 Chemical Reaction Types III. Single Displacement (or single replacement) A + BC  AC + B Because A is more reactive than B! Many metals dissolve in (react with) acid and release flammable hydrogen gas! Exceptions: Cu, Au, Ag (N.R. in most acids) Group I metals react with H 2 O and exotherm!

Jean Lee Lin Chem 2 Chapter 6 & 75 Chemical Reaction Types IV. Double Displacement (exchange partners, p.192) AD + BC  AC + BD (a) Precipitation Rx. : to form insoluble product(s) (p.174) (b) Acid- base neutralization Rx.( p.186-7) HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) + heat Acid: H + Base: OH - Salt water Definition: Acid and Base

Jean Lee Lin Chem 2 Chapter 6 & 76 V. Oxidation-Reduction “Redox”, involves electron-transfer (p ) (a) Formation of ionic compound ( by metal + non-metal) 2 Na (s) + Cl 2(g)  2 Na + Cl - (s) (Fig p.110) OIL: Oxidation is loss of electron (metals) RIG: Reduction is gain of electron (non-metals) Q: Is single displacement also redox? (b) Combustion – burning a substance in O 2 or air to produce heat (or energy), (p slide 2) Green house effect & global warming! Q: Hydrogen: a clean fuel for rocket (p.195), potential energy for the future! Q: Is combustion also synthesis? Do self check 7.4 p.199 for review!

Jean Lee Lin Chem 2 Chapter 6 & 77 4 Driving Forces for Chem.Rx. Formation of Solid e.g. precipitation rx. Formation of water e.g. acid-base rx. Formation of Gas Transfer of Electrons (redox) Note: color change & temperature change are important clues of chem. rx. but NOT driving forces (p.173)!

Jean Lee Lin Chem 2 Chapter 6 & 78 Solubility Soluble vs. insoluble solid  Homogeneous vs. heterogeneous solutions  Slightly soluble is considered insoluble  Strong electrolytes (salt readily dissociate to form ions in water and efficiently conduct electricity), e.g. NaCl, HCl, strong acid/base are strong electrolytes, Fig. 7.2 p.175  Weak electrolytes (NH 4 OH, acetic acid): weak acid/base can not produce many ions in water  Non-electrolytes (sugar), no ions formed when dissolved in water incapable of “ionic conductivity”  Q: Is molten NaCl (l) conductive ?

Jean Lee Lin Chem 2 Chapter 6 & 79 Writing cations and anions from ionic compounds  Ex. p.176 (important exercise)  Must include (aq) for ions Mix two chemical reagents (already dissolved in water) to predict salt precipitation (i.e. insoluble ionic compounds ppt.)  use “Solubility Rules” Table 7.1, p.178

Jean Lee Lin Chem 2 Chapter 6 & 710 Solubility Rules Good Drivers for ppt Pb +2 PO 4 -3, CO 3 -2, Cr 2 O 7 -2, S -2, OH - (except Ca +2, Ba +2, Sr +2 ) Example: Self 7.1 p.183 HW#21,22 p.202 Good Dissolvers “Spectator ions” NO 3 -, Na +, K +, NH 4 + Cl -, Br -, I - (except Ag +, Pb +2, Hg 2 +2 ) SO 4 -2 (except Ca +2, Ba +2, Pb +2 )

Jean Lee Lin Chem 2 Chapter 6 & 711 Equation writing (3 Types of description in Aqueous Solution) (i) Molecular Equation (ii) Complete Ionic (iii) Net Ionic Common mistakes! Na 2 Cl 2 (aq) vs. 2 NaCl(aq) K 2 (NO 3 ) 2 vs. 2 KNO 3 (aq) Q: What is the net ionic equation for acid-base neutralization?