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9MnO, + 80H” half-reaction: Br” + 6OH” — BrOy7 + 3H,0 + Ge” 6, Combine the two half-reactions. (a) First, add the equations of the - two half-reactions as they are wntten: 2Mu047 + 4H50 + 6e7 + Br” + 60H” — 92MnOs + 80H” + BrOs7 + 3H50 + Ge” (b) Next, simplify the balanced equation. by canceling like species on both sides of the equation. In this example, be”, 3H,0, and 60H” can be canceled: 2MnO, + H50 + Br” — 2MnO» + 20H" + BrOs” (c) Finally, insert the state of cach species: 9MnOw (aq) + HoO(1) + Br (ag) —> 9MnOs(s) + 20H (ag) + BrOs (ag) This expression is the fully balanced net ionic equation. It wovld have been very difficult to balence such à complicated equation without breaking it down into half-reactions and working systemati- ca!ly on each of them. “This chapter has concentrated on the qualitative aspects of reactions. The three types of reactions introduced here have key features in com- mon, às we explain in later chapters. Precipitation reactions are dealt with in Chapter 15. Acids and bases are so important that we devote two chapters, Chapters 14 and 15, to their properties. We have not explained how we know what substances can oxidize or reduce a given substance. Fhis point is taken up in Chapter 17, where we also see how redox reactions are used to generate electricity. SUMMARY 3.1 and 3.2 A chemical reaction is summarized by writ- ing its chemical equation. The var jeties of chemical re- actions commonly encountered in chenustry are summa- rized in Table 3.1, À chemical equation summarizes qualitative information about the identíties of the reac- tants, the starting materials, and the products, the mate- rials formed. When the skeletal equation is balanced by including the stoichiometric coefficierts, it also ex- ses the fact that no atoms are created or destroyedin repla: se of the reaction. 3.4 A precipitatio partners. The solubility rules (Table 3.9), a summary ol cópia 92 mm 4 rats DATA h / 3.3 In a precipitation reaction à solid is formed when two solutions are mixed. The essential feature ofa pre- cipitation reaction (and other reactions involving ions) às made clear by writing the net ionic equation, which is derived by canceling the spectator ions, tie ions left unchanged by the reacúon. n reaction is a special case ola double- cement reaction in which atoms or ions exchange Scanned by CamScanner 
