1. John C. Kotz State University of New York, College at Oneonta John C. Kotz Paul M. Treichel John Townsend http://academic.cengage.com/kotz Chapter 3 Chemical Reactions

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3. 3 © 2009 Brooks/Cole - Cengage CHEMICAL REACTIONS Chapter 3 Reactants: Zn + I 2 Product: ZnI 2

4. 4 © 2009 Brooks/Cole - Cengage Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O 2 (g) f 2 Al 2 O 3 (s) The numbers in the front are called stoichiometric coefficients The letters (s), (g), and (s) are the physical states of compounds.

5. 5 © 2009 Brooks/Cole - Cengage Reaction of Phosphorus with Cl 2 Notice the stoichiometric coefficients and the physical states of the reactants and products.

6. 6 © 2009 Brooks/Cole - Cengage Reaction of Iron with Cl 2 Notice the stoichiometric coefficients and the physical states of the reactants and products.

7. 7 © 2009 Brooks/Cole - Cengage Chemical Equations 4 Al(s) + 3 O 2 (g) f 2 Al 2 O 3 (s) This equation means 4 Al atoms + 3 O 2 molecules f 2 “molecules” of Al 2 O 3 2 “molecules” of Al 2 O 3 4 moles of Al + 3 moles of O 2 f 2 moles of Al 2 O 3 2 moles of Al 2 O 3

8. 8 © 2009 Brooks/Cole - Cengage Chemical Equations Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change.Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change. The Law of the Conservation of MatterThe Law of the Conservation of Matter 2HgO(s) f 2 Hg(liq) + O 2 (g) PLAY MOVIE

9. 9 © 2009 Brooks/Cole - Cengage Because of the principle of the conservation of matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Chemical Equations Lavoisier, 1788

10. 10 © 2009 Brooks/Cole - Cengage Balancing Equations ___ Al(s) + ___ Br 2 (s) f ___ Al 2 Br 6 (s) PLAY MOVIE

11. 11 © 2009 Brooks/Cole - Cengage Balancing Equations ____C 3 H 8 (g) + _____ O 2 (g) f _____CO 2 (g) + _____ H 2 O(g) ____B 4 H 10 (g) + _____ O 2 (g) f ___ B 2 O 3 (g) + _____ H 2 O(g) PLAY MOVIE

12. 12 © 2009 Brooks/Cole - Cengage Chemical Equilibrium Chemical reactions are reversible. Chemical reactions are reversible. Ammonia can be produced from the elements in the Haber process Ammonia can be produced from the elements in the Haber process N 2 (g) + 3 H 2 (g) f 2 NH 3 (g) But NH 3 can also be decomposed to the elements But NH 3 can also be decomposed to the elements 2 NH 3 (g) f N 2 (g) + 3 H 2 (g) 2 NH 3 (g) f N 2 (g) + 3 H 2 (g) In a process to make NH 3, the reaction can come eventually to equilbrium. In a process to make NH 3, the reaction can come eventually to equilbrium. N 2 (g) + 3 H 2 (g) e 2 NH 3 (g) Double arrows indicate equilibrium Double arrows indicate equilibrium

13. 13 © 2009 Brooks/Cole - Cengage Reaction Reversibility Stalactites and stalagmites in caves depend on a reversible chemical reaction Ca 2+ (aq) + 2 HCO 3 – (aq) e CaCO 3 (s) + CO 2 (g) + H 2 O(s)

14. 14 © 2009 Brooks/Cole - Cengage Reaction Reversibility

15. 15 © 2009 Brooks/Cole - Cengage Chemical Equilibrium Once equilibrium is achieved, reaction continues, but there is no net change in amounts of products or reactants.

16. 16 © 2009 Brooks/Cole - Cengage Reactions in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO 4 in water K + (aq) + MnO 4 - (aq) PLAY MOVIE

17. 17 © 2009 Brooks/Cole - Cengage An Ionic Compound, CuCl 2, in Water

18. 18 © 2009 Brooks/Cole - Cengage How do we know ions are present in aqueous solutions? The solutions conduct electricity! They are called ELECTROLYTES HCl, CuCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions

19. 19 © 2009 Brooks/Cole - Cengage HCl, CuCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions PLAY MOVIE

20. 20 © 2009 Brooks/Cole - Cengage Aqueous Solutions Acetic acid ionizes only to a small extent, so it is a weak electrolyte. CH 3 CO 2 H(aq) e CH 3 CO 2 - (aq) + H + (aq) PLAY MOVIE

21. 21 © 2009 Brooks/Cole - Cengage Aqueous Solutions Acetic acid ionizes only to a small extent, so it is a weak electrolyte. CH 3 CO 2 H(aq) e CH 3 CO 2 - (aq) + H + (aq)

22. 22 © 2009 Brooks/Cole - Cengage Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugarethanol ethylene glycol Examples include: sugarethanol ethylene glycol

23. 23 © 2009 Brooks/Cole - Cengage Water Solubility of Ionic Compounds If one ion from the “Soluble Compd.” list is present in a compound, the compound is water soluble.

24. 24 © 2009 Brooks/Cole - Cengage Water Solubility of Ionic Compounds Common minerals are often formed with anions that lead to insolubility: sulfidefluoride sulfidefluoride carbonateoxide carbonateoxide Azurite, a copper carbonate Iron pyrite, a sulfide Orpiment, arsenic sulfide

25. 25 © 2009 Brooks/Cole - Cengage Chemical Reactions in Water We will look at EXCHANGE REACTIONS Pb(NO 3 ) 2 (aq) + 2 KI(aq) f PbI 2 (s) + 2 KNO 3 (aq) The anions exchange places between cations. PLAY MOVIE

26. 26 © 2009 Brooks/Cole - Cengage Precipitation Reactions The “driving force” is the formation of an insoluble compound — a precipitate. Pb(NO 3 ) 2 (aq) + 2 KI(aq) f 2 KNO 3 (aq) + PbI 2 (s) 2 KNO 3 (aq) + PbI 2 (s) BaCl 2 (aq) + Na 2 SO 4 (aq) f BaSO 4 (s) + 2 NaCl(aq)

27. 27 © 2009 Brooks/Cole - Cengage Net Ionic Equations Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq) f PbCrO 4 (s) + 2 KNO 3 (aq) This is the “complete equation” Because Pb(NO 3 ) 2 and K 2 CrO 4 are strong electrolytes we should write Pb 2+ (aq) + 2 NO 3 - (aq) + 2 K + (aq) + CrO 4 2- (aq) f PbCrO 4 (s) + 2 K + (aq) + 2 NO 3 - (aq) f PbCrO 4 (s) + 2 K + (aq) + 2 NO 3 - (aq) This is the “ionic equation” Question: do we need to include the K + and NO 3 - ions? PLAY MOVIE

28. 28 © 2009 Brooks/Cole - Cengage Net Ionic Equations Ionic equation: Pb 2+ (aq) + 2 NO 3 - (aq) + 2 K + (aq) + CrO 4 2- (aq) f PbCrO 4 (s) + 2 K + (aq) + 2 NO 3 - (aq) f PbCrO 4 (s) + 2 K + (aq) + 2 NO 3 - (aq) We leave the spectator ions out — Pb 2+ (aq) + CrO 4 2- (aq) f PbCrO 4 (s) NET IONIC EQUATION to give the NET IONIC EQUATION The NO 3 - and K + ions are SPECTATOR IONS — they do not participate. Could have used Na + instead of K +.

29. 29 © 2009 Brooks/Cole - Cengage An acid f H 3 O + in water ACIDSACIDS PLAY MOVIE

30. 30 © 2009 Brooks/Cole - Cengage The Nature of Acids PLAY MOVIE

31. 31 © 2009 Brooks/Cole - Cengage An acid f H 3 O + in water ACIDS Some strong acids are HClhydrochloric H 2 SO 4 sulfuric HClO 4 perchloric HNO 3 nitric HNO 3

32. 32 © 2009 Brooks/Cole - Cengage Weak Acids WEAK ACIDS = weak electrolytes CH 3 CO 2 Hacetic acid H 2 CO 3 carbonic acid H 3 PO 4 phosphoric acid HFhydrofluoric acid Acetic acid PLAY MOVIE

33. 33 © 2009 Brooks/Cole - Cengage ACIDS Nonmetal oxides can be acids CO 2 (aq) + H 2 O(s) f H 2 CO 3 (aq) SO 3 (aq) + H 2 O(s) f H 2 SO 4 (aq) and can come from burning coal and oil.

34. 34 © 2009 Brooks/Cole - Cengage Base f OH - in water BASES Table 3.2 NaOH(aq) f Na + (aq) + OH - (aq) NaOH is a strong base PLAY MOVIE

35. 35 © 2009 Brooks/Cole - Cengage Ammonia, NH 3 Ammonia, NH 3 An Important Base PLAY MOVIE

36. 36 © 2009 Brooks/Cole - Cengage BASES Metal oxides are bases CaO(s) + H 2 O(s) f Ca(OH) 2 (aq) f Ca(OH) 2 (aq) CaO in water. Indicator shows solution is basic.

37. 37 © 2009 Brooks/Cole - Cengage Know the strong acids & bases!

38. 38 © 2009 Brooks/Cole - Cengage Acid-Base Reactions The “driving force” is the formation of water.The “driving force” is the formation of water. NaOH(aq) + HCl(aq) f NaCl(aq) + H 2 O(liq) Net ionic equationNet ionic equation OH - (aq) + H 3 O + (aq) f 2 H 2 O(s) OH - (aq) + H 3 O + (aq) f 2 H 2 O(s) This applies to ALL reactions of STRONG acids and bases.This applies to ALL reactions of STRONG acids and bases. PLAY MOVIE

39. 39 © 2009 Brooks/Cole - Cengage See Active Figure 3.14

40. 40 © 2009 Brooks/Cole - Cengage Acid-Base Reactions A-B reactions are sometimes called NEUTRALIZATIONS because the solution is neither acidic nor basic at the end.A-B reactions are sometimes called NEUTRALIZATIONS because the solution is neither acidic nor basic at the end. The other product of the A-B reaction is a SALT, MX.The other product of the A-B reaction is a SALT, MX. HX + MOH f MX + H 2 O HX + MOH f MX + H 2 O M n+ comes from base & X n- comes from acid M n+ comes from base & X n- comes from acid This is one way to make compounds! This is one way to make compounds!

41. 41 © 2009 Brooks/Cole - Cengage Gas-Forming Reactions This is primarily the chemistry of metal carbonates. CO 2 and water f H 2 CO 3 H 2 CO 3 (aq) + Ca 2+ f H 2 CO 3 (aq) + Ca 2+ f 2 H + (aq) + CaCO 3 (s) (limestone) 2 H + (aq) + CaCO 3 (s) (limestone) Adding acid reverses this reaction. MCO 3 + acid f CO 2 + salt

42. 42 © 2009 Brooks/Cole - Cengage Gas-Forming Reactions CaCO 3 (s) + H 2 SO 4 (aq) f 2 CaSO 4 (s) + H 2 CO 3 (aq) 2 CaSO 4 (s) + H 2 CO 3 (aq) Carbonic acid is unstable and forms CO 2 & H 2 O H 2 CO 3 (aq) f CO 2 + water (Antacid tablet has citric acid + NaHCO 3 ) PLAY MOVIE

43. 43 © 2009 Brooks/Cole - Cengage

44. 44 © 2009 Brooks/Cole - Cengage Oxidation-Reduction Reactions Section 3.9 Thermite reaction Fe 2 O 3 (s) + 2 Al(s) f 2 Fe(s) + Al 2 O 3 (s)

45. 45 © 2009 Brooks/Cole - Cengage REDOX REACTIONS EXCHANGEAcid-BaseReactionsEXCHANGEGas-FormingReactions EXCHANGE: Precipitation Reactions REACTIONS

46. 46 © 2009 Brooks/Cole - Cengage REDOX REACTIONS REDOX = reduction & oxidation O 2 (g) + 2 H 2 (g) f 2 H 2 O(s) O 2 (g) + 2 H 2 (g) f 2 H 2 O(s)

47. 47 © 2009 Brooks/Cole - Cengage REDOX REACTIONS REDOX = reduction & oxidation Corrosion of aluminum 2 Al(s) + 3 Cu 2+ (aq) f 2 Al 3+ (aq) + 3 Cu(s)

48. 48 © 2009 Brooks/Cole - Cengage In all reactions if something has been oxidized then something has also been reduced REDOX REACTIONS Cu(s) + 2 Ag + (aq) f Cu 2+ (aq) + 2 Ag(s) PLAY MOVIE

49. 49 © 2009 Brooks/Cole - Cengage Cu(s) + 2 Ag + (aq) f Cu 2+ (aq) + 2 Ag(s) REDOX REACTIONS

50. 50 © 2009 Brooks/Cole - Cengage Why Study Redox Reactions Manufacturing metals CorrosionCorrosion BatteriesBatteries FuelsFuels

51. 51 © 2009 Brooks/Cole - Cengage Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor. Transfer leads to— 1. increase in oxidation number of some element = OXIDATION 2.decrease in oxidation number of some element = REDUCTION REDOX REACTIONS

52. 52 © 2009 Brooks/Cole - Cengage 2.In simple ions, ox. no. = charge on ion. -1 for Cl - +2 for Mg 2+ -1 for Cl - +2 for Mg 2+ 2.In simple ions, ox. no. = charge on ion. -1 for Cl - +2 for Mg 2+ -1 for Cl - +2 for Mg 2+ 1.Each atom in free element has ox. no. = 0. Zn O 2 I 2 S 8 Zn O 2 I 2 S 8 1.Each atom in free element has ox. no. = 0. Zn O 2 I 2 S 8 Zn O 2 I 2 S 8 OXIDATION NUMBERS The electric charge an element APPEARS to have when electrons are counted by some arbitrary rules:

53. 53 © 2009 Brooks/Cole - Cengage 5.Algebraic sum of oxidation numbers = 0 for a compound = 0 for a compound = overall charge for an ion = overall charge for an ion 5.Algebraic sum of oxidation numbers = 0 for a compound = 0 for a compound = overall charge for an ion = overall charge for an ion 4.Ox. no. of H = +1 (except when H is associated with a metal as in NaH where it is -1) 4.Ox. no. of H = +1 (except when H is associated with a metal as in NaH where it is -1) 3.O has ox. no. = -2 (except in peroxides: in H 2 O 2, O = -1) 3.O has ox. no. = -2 (except in peroxides: in H 2 O 2, O = -1) OXIDATION NUMBERS

54. 54 © 2009 Brooks/Cole - Cengage OXIDATION NUMBERS NH 3 N = ClO - Cl = H 3 PO 4 P = MnO 4 - Mn = Cr 2 O 7 2- Cr = C 3 H 8 C = Oxidation number of F in HF?

55. 55 © 2009 Brooks/Cole - Cengage Recognizing a Redox Reaction Corrosion of aluminum 2 Al(s) + 3 Cu 2+ (aq) f 2 Al 3+ (aq) + 3 Cu(s) Al(s) f Al 3+ (aq) + 3 e - Ox. no. of Al increases as e - are donated by the metal.Ox. no. of Al increases as e - are donated by the metal. Therefore, Al is OXIDIZEDTherefore, Al is OXIDIZED Al is the REDUCING AGENT in this balanced half- reaction.Al is the REDUCING AGENT in this balanced half- reaction.

56. 56 © 2009 Brooks/Cole - Cengage Recognizing a Redox Reaction Corrosion of aluminum 2 Al(s) + 3 Cu 2+ (aq) f 2 Al 3+ (aq) + 3 Cu(s) Cu 2+ (aq) + 2 e - f Cu(s) Ox. no. of Cu decreases as e - are accepted by the ion.Ox. no. of Cu decreases as e - are accepted by the ion. Therefore, Cu is REDUCEDTherefore, Cu is REDUCED Cu is the OXIDIZING AGENT in this balanced half- reaction.Cu is the OXIDIZING AGENT in this balanced half- reaction.

57. 57 © 2009 Brooks/Cole - Cengage Recognizing a Redox Reaction Notice that the 2 half-reactions add up to give the overall reaction —if we use 2 mol of Al and 3 mol of Cu 2+. 2 Al(s) f 2 Al 3+ (aq) + 6 e - 2 Al(s) f 2 Al 3+ (aq) + 6 e - 3 Cu 2+ (aq) + 6 e - f 3 Cu(s) 3 Cu 2+ (aq) + 6 e - f 3 Cu(s)----------------------------------------------------------- 2 Al(s) + 3 Cu 2+ (aq) f 2 Al 3+ (aq) + 3 Cu(s) Final eqn. is balanced for mass and charge.

58. 58 © 2009 Brooks/Cole - Cengage Examples of Redox Reactions Metal + halogen 2 Al + 3 Br 2 f Al 2 Br 6 PLAY MOVIE

59. 59 © 2009 Brooks/Cole - Cengage Examples of Redox Reactions Metal (Mg) + Oxygen f MgO Nonmetal (P) + Oxygen f P 4 O 10 PLAY MOVIE

60. 60 © 2009 Brooks/Cole - Cengage Recognizing a Redox Reaction See Table 3.4 In terms of oxygengainloss In terms of halogengainloss In terms of electronslossgain Reaction Type OxidationOxidationReductionReduction

61. 61 © 2009 Brooks/Cole - Cengage Common Oxidizing and Reducing Agents See Table 3.4 HNO 3 is an oxidizing agent 2 K + 2 H 2 O f 2 KOH + H 2 Metals (Na, K, Mg, Fe) are reducing agents Metals (Cu) are reducing agents Cu + HNO 3 f Cu 2+ + NO 2

62. 62 © 2009 Brooks/Cole - Cengage Examples of Redox Reactions Metal + acid Mg + HCl Mg = reducing agent H + = oxidizing agent Metal + acid Cu + HNO 3 Cu = reducing agent HNO 3 = oxidizing agent PLAY MOVIE