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Chapter 11 Chemistry Chemical Reactions 11.1 Describing Chemical Reactions n Reactants are on the left side of the equation. n Products are on the right side of the equation. n A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products. n A catalyst is a substance that speeds up the reaction but is not used up in the reaction. n See Table 11.1 on page 323 for Symbols used in chemical equations. 11.1 cont n To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass. n H2 + O2 à H2O n 2H2 + O2 à 2H2O Conceptual Problem 11.2 Practice Problem #3 page 327 Practice Problem #4 page 327 Practice problem #5 page 328 Practice problem #6 page 328 Predicting Products (AKA: Soap opera Chemistry) Five types of reactions: • Synthesis (Combination) • Decomposition • Single Replacement • Double Replacement • Combustion 1. Synthesis (or Combination) Two or more substances react to form ONE product A + B à AB The soap opera begins . . . Rob + Sally à Rob/Sally + à Demo #1: Synthesis Reaction Remember to balance the equation! 2 Mg(s) + O2(g) à 2 MgO (s) 2. Decomposition A compound breaks down into simpler substances. A decomposition reaction requires heat, light, electricity, or a chemical catalyst AB à A + B Drama with Rob and Sally . .. Rob/Sally à Rob + Sally à + Demo #2: Decomposition Reaction Remember to balance the equation! KI 2 H2O2(aq) à 2 H O + O 2 (l) 2(g) 3. Single Replacement Reaction n Atoms in single element replace the atoms in a compound n Can be cationic or anionic . . . n A metal replaces the cation in the compound n A nonmetal replaces the anion in the compound Cationic SR: A is a metal element, B is cation (+) A +BC à AC + B Anionic SR: C is a non-metal element, D is anion (-) C + BD à BC + D How can you know if one metal will displace another? Li n Look on the Activity Series of K Metals Chart . . . Page 333. (Compare this with your PT) Ca n A reactive metal will replace any Na metal listed below it. Mg Will this React? Al Mg + ZnCl2 à YES ! Zn MgCl2 + Zn Will this React? … Mg + CaCl2 à NO Reaction! Mg is lower than Ca Along comes Brian . . . Brian + Rob/Sally à Brian/Sally + Rob + à + Demo #3: Single Replacement Reaction Mg(s) + 2 HCl(aq) à MgCl2(aq) + H2(g) Demo #4: Single Replacement Reaction + 2Al + 3 CuCl 2 à 2 AlCl 3 3Cu Remember to balance the equation! 4. Double Replacement Reaction Compounds exchange cations AB + CD à CB + AD Drama at the prom . . . Rob/Pam + Brian/Sally à Brian/Pam + Rob/Sally + + à Demo #5: Double Replacement Reaction 2 2 Pb(NO3)2(aq) + KI(aq)à KNO3(aq) + PbI2(s) Remember to balance the equation! 5. Combustion An element or compound reacts with O2 producing energy as heat and light. Example: Mg(s) + O2(g) à MgO(s) Complete combustion of a hydrocarbon yields CO2 and H2O Example: C3H8 + O2 à CO2 + H2O The Soap opera Ends L Brian + O2 à CO2 + H2O (A hydrocarbon) Oh No! à Demo#6: Combustion To get our H2, we will first do a single replacement reaction: 2 Zn + HCl à ZnCl2 + H2 H2 + O2 à H2O + Energy! 2 2 Remember to balance the equation! Homework 11.1 and 11.2 n Review worksheet 11.1 and 11.2 n Section Assessment 7-12 page 329 n Section Assessment 22-27 page 339 Section 11.3 Reactions in Aqueous Solutions n A complete ionic equation is an equation that shows dissolved ionic compounds as dissociated free ions. n Ex n An ion that appears on both sides of an equation and is not directly involved in the reaction is called a spectator ion. 11.3 Cont. n The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change. n Ex. Conceptual Problem 11.9 page 343 Practice problem #28 page 343 Practice Problem #29 page 343 11.3 Cont. n You can predict the formation of a precipitate by using the general rules for solubility on ionic compounds. Table 11.3 page 344. Table 11.3 Compounds Solubility Salts of alkali metals and Soluble ammonia Nitrate salts and chlorate salts Soluble Sulfate salts, except compounds Soluble with Pb2+, Ag+, Hg22+, Ba2+, Sr2+, and Ca2+ Chloride salts except compounds Soluble with Ag+, Pb2+, and Hg22+ Carbonates, Phosphates, Most are insoluble chromates, sulfides, and hydroxides Homework 11.3 n Section Assessment page 344 (#30-35) n Review Worksheet n Review how to write and balance chemical equations.
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