1. Chapter 7 Chemical Reactions

2. Day One and Two Tro's "Introductory Chemistry", Chapter 72

3. Day Three Tro's "Introductory Chemistry", Chapter 73

4. Chemical Reactions  Reactions: chemical changes in matter resulting in new substances  Reactions involve rearrangement and exchange of atoms to produce new molecules Elements DO NOT CHANGE during a reaction. Atoms of different elements can combine to make new compounds Molecules can decompose into smaller molecules or atoms Atoms can gain or lose electrons, turning them into ions. ○ Or changing the charge on ions that are already there. Tro's "Introductory Chemistry", Chapter 74

5. Combustion Reactions  Reactions in which O 2 is consumed by combining with another substance are called combustion reactions. 5 Reactants  Products

6. Precipitation Reactions  Combining of ions resulting in formation of a material that is insoluble in water: precipitation reactions Tro's "Introductory Chemistry", Chapter 76

7. Evidence of Chemical Reactions  Look for evidence of a new substance  Visual clues (permanent) Color change Precipitate formation ○ Solid that forms when liquid solutions are mixed Gas bubbles Large energy changes ○ Container becomes very hot or cold ○ Emission of light  Other clues. New odor Whooshing sound from a tube Permanent new state Tro's "Introductory Chemistry", Chapter 77

8. Evidence of Chemical Change 8Tro's "Introductory Chemistry", Chapter 7 Color Change Formation of Solid Precipitate Formation of a Gas Emission of Light Release or Absorption of Heat

9. Practice—Decide Whether Each of the Following Involve a Chemical Reaction. Tro's "Introductory Chemistry", Chapter 79 Photosynthesis Heating sugar until it turns black Heating ice until it turns liquid Digestion of food Dissolving sugar in water Yes, CO 2 and H 2 O combine into carbohydrates Yes, sugar decomposing No, molecules still same Yes, food decomposing and combining with stomach acid No, molecules still same

10. Chemical Equations  Short-hand way of describing a reaction.  Provides information about the reaction. Formulas of reactants and products. States of reactants and products. Relative numbers of reactant and product molecules that are required. Can be used to determine masses of reactants used and products that can be made. Tro's "Introductory Chemistry", Chapter 710

11. Conservation of Mass  Matter cannot be created or destroyed. Therefore, the total mass cannot change. mass of reactants = total mass of products.  In a chemical reaction, all the atoms present at the beginning are still present at the end. If all the atoms are still there, then the mass will not change. Tro's "Introductory Chemistry", Chapter 711

12. The Combustion of Methane  Methane gas burns to produce carbon dioxide gas and gaseous water. Whenever something burns it combines with O 2 (g). Tro's "Introductory Chemistry", Chapter 712

13. Combustion of Methane  Methane gas burns to produce carbon dioxide gas and gaseous water. Whenever something burns it combines with O 2 (g). CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O(g)

14. Assignment  Problem Set #1 Page 232 ○ #29- 33 Tro's "Introductory Chemistry", Chapter 714

15. Day Four Tro's "Introductory Chemistry", Chapter 715

16. Chemical Equations  CH 4 and O 2 are the reactants, and CO 2 and H 2 O are the products.  The (g) after the formulas tells us the state of the chemical.  The number in front of each substance tells us the numbers of those molecules in the reaction. Called the coefficients. Tro's "Introductory Chemistry", Chapter 716 CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g)

17. Symbols Used in Equations  Symbols used to indicate state after chemical. (g) = gas; (l) = liquid; (s) = solid. (aq) = aqueous = dissolved in water.  Energy symbols used above the arrow for decomposition reactions.  = heat. h = light. shock = mechanical. elec = electrical. Tro's "Introductory Chemistry", Chapter 717

18. Balancing Equations 1. Write the CORRECT formulas for each compound (silicon dioxide + carbon  silicon carbide + carbon monoxide) 2. If element occurs in only one compound balance first. Balance METALS first. Tro's "Introductory Chemistry", Chapter 718

19. Balancing Equations, cont. 3. If element occurs as a FREE element, balance LAST. 4. Check to make sure equation is balanced. Tro's "Introductory Chemistry", Chapter 719 SiO 2 + C  SiC + CO

20. Example  When magnesium metal burns in air, it produces a white, powdery compound magnesium oxide. 1. Write a skeletal equation 2. Count the number of atoms on each side.  Mg   O  Tro's "Introductory Chemistry", Chapter 720

21. Another Example  Under appropriate conditions at 1000°C, ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide and steam Tro's "Introductory Chemistry", Chapter 721

22. Practice #1 When aluminum metal reacts with air, it produces a white, powdery compound called aluminum oxide. Tro's "Introductory Chemistry", Chapter 722

23. Practice #2 Acetic acid reacts with the metal aluminum to make aqueous aluminum acetate and gaseous hydrogen. Acids are always aqueous. Metals are solid except for mercury. Tro's "Introductory Chemistry", Chapter 723

24. Practice #3 Combustion of ethyl alcohol (C 2 H 5 OH) in flambé (a brandied flaming dessert). Tro's "Introductory Chemistry", Chapter 724

25. Practice #4 Combustion of liquid butane (C 4 H 10 ) in a lighter. C 4 H 10 (l) + O 2 (g)  CO 2 (g) + H 2 O(g) Tro's "Introductory Chemistry", Chapter 725

26. Assignment  Problem Set #2 Page 233 ○ #37, 38, 39 Tro's "Introductory Chemistry", Chapter 726

27. Day Five Tro's "Introductory Chemistry", Chapter 727

28. Aqueous Solutions  Chemicals we are react together are most of the time dissolved in water Mixtures of a chemical dissolved in water are called aqueous solutions  Dissolving the chemicals in water helps them to react together faster The water separates the chemicals into individual molecules or ions The separate, free-floating particles come in contact more frequently so the reaction speeds up Tro's "Introductory Chemistry", Chapter 728

29. Predicting Whether a Reaction Will Occur in Aqueous Solution  “Forces” that drive a reaction: Formation of a solid. Formation of water. Formation of a gas. Transfer of electrons.  When chemicals (dissolved in water) are mixed and one of the above-noted forces occur, the reaction will generally happen. Tro's "Introductory Chemistry", Chapter 729

30. Dissociation  When ionic compounds dissolve in water, the anions and cations are separated from each other. This is called dissociation. However, not all ionic compounds are soluble in water!  When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion. Tro's "Introductory Chemistry", Chapter 730

31. Dissociation, Continued  Potassium iodide dissociates in water into potassium cations and iodide anions. KI(aq) → K +1 (aq) + I -1 (aq)  Copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions. CuSO 4 (aq) → Cu +2 (aq) + SO 4 -2 (aq) Tro's "Introductory Chemistry", Chapter 731 K +1 I -1 K I Cu +2 SO 4 -2 Cu SO 4

32. Dissociation, Continued  Potassium sulfate dissociates in water into potassium cations and sulfate anions. K 2 SO 4 (aq) → 2 K +1 (aq) + SO 4 -2 (aq) Tro's "Introductory Chemistry", Chapter 732 K +1 SO 4 -2 K +1 KK SO 4

33. Electrolytes  Electrolytes are substances whose water solution is a conductor of electricity  All electrolytes have ions dissolved in water Tro's "Introductory Chemistry", Chapter 733

34. Electrolytes, Continued  In strong electrolytes, all the electrolyte molecules or formula units are separated into ions  In nonelectrolytes, none of the molecules are separated into ions  In weak electrolytes, a small percentage of the molecules are separated into ions Tro's "Introductory Chemistry", Chapter 734

35. Types of Electrolytes  Salts = Water soluble ionic compounds. All strong electrolytes.  Acids = Form H +1 ions and anions in water solution. In binary acids, the anion is monoatomic. In oxyacids, the anion is polyatomic. Sour taste. React and dissolve many metals. Strong acid = strong electrolyte, weak acid = weak electrolyte.  Bases = Water-soluble metal hydroxides. Bitter taste, slippery (soapy) feeling solutions. Increases the OH -1 concentration. Tro's "Introductory Chemistry", Chapter 735

36. When Will a Salt Dissolve?  A compound is soluble in a liquid if it dissolves in that liquid. NaCl is soluble in water, but AgCl is not.  A compound is insoluble if a significant amount does not dissolve in that liquid. AgCl is insoluble in water. ○ Though there is a very small amount dissolved, but not enough to be significant. Tro's "Introductory Chemistry", Chapter 736

37. Solubility Rules: Compounds that Are Generally Soluble in Water 37Tro's "Introductory Chemistry", Chapter 7 Compounds containing the following ions are generally soluble Exceptions (when combined with ions on the left the compound is insoluble) Li +, Na +, K +, NH 4 + none NO 3 –, C 2 H 3 O 2 – none Cl –, Br –, I – Ag +, Hg 2 2+, Pb 2+ SO 4 2– Ca 2+, Sr 2+, Ba 2+, Pb 2+

38. Solubility Rules: Compounds that Are Generally Insoluble 38Tro's "Introductory Chemistry", Chapter 7 Compounds containing the following ions are generally insoluble Exceptions (when combined with ions on the left the compound is soluble or slightly soluble) OH – Li +, Na +, K +, NH 4 +, Ca 2+, Sr 2+, Ba 2+ S 2– Li +, Na +, K +, NH 4 +, Ca 2+, Sr 2+, Ba 2+ CO 3 2–, PO 4 3– Li +, Na +, K +, NH 4 +

39. Determine if Each of the Following Is Soluble in Water  KOH  AgBr  CaCl 2  Pb(NO 3 ) 2  PbSO 4 Tro's "Introductory Chemistry", Chapter 739

40. Determine if Each of the Following Is Soluble in Water, Continued  KOHSoluble, because the cation is K +.  AgBrInsoluble, even though most compounds with Br − are soluble, this is an exception.  CaCl 2 Soluble, most compounds with Cl − are soluble.  Pb(NO 3 ) 2 Soluble, because the anion is NO 3 −.  PbSO 4 Insoluble, even though most compounds with SO 4 2− are soluble, this is an exception. Tro's "Introductory Chemistry", Chapter 740

41. Precipitation Reactions  If the ion exchange results in forming a compound that is insoluble in water, it will come out of solution as a precipitate. Tro's "Introductory Chemistry", Chapter 741

42. Precipitation Reactions, Continued 42Tro's "Introductory Chemistry", Chapter 7 2 KI(aq) + Pb(NO 3 ) 2 (aq)  2 KNO 3 (aq) + PbI 2 (s)

43. No Precipitate Formation = No Reaction 43Tro's "Introductory Chemistry", Chapter 7 KI(aq) + NaCl(aq)  KCl(aq) + NaI(aq) All ions still present,  no reaction.

44. Process for Predicting the Products of a Precipitation Reaction 1. Write the formula for the reactants and Determine what ions each aqueous reactant has. 2. Exchange ions. (+) ion from one reactant with (-) ion from the other. 3. Balance charges of combined ions to get formula of each product. 4. Balance the equation. Count atoms. 5. Determine solubility of each product in water. Use the solubility rules. If product is insoluble or slightly soluble, it will precipitate. If neither product will precipitate, no reaction. Tro's "Introductory Chemistry", Chapter 744

45. Example 7.7—When an Aqueous Solution of Sodium Carbonate Is Added to an Aqueous Solution of Copper(II) Chloride, a White Solid Forms. 1. Write the formulas of the reactants and Determine the ions present when each reactant dissociates. Na 2 CO 3 (aq) + CuCl 2 (aq)  2. Exchange the ions. Tro's "Introductory Chemistry", Chapter 745

46. Practice–Predict the Products and Balance the Equation  KCl(aq) + AgNO 3 (aq)   Na 2 S(aq) + CaCl 2 (aq)  Tro's "Introductory Chemistry", Chapter 746

47. Assignment  Problem Set #3 #61, 67, 70 Tro's "Introductory Chemistry", Chapter 747

48. Day Six Tro's "Introductory Chemistry", Chapter 748

49. Day Seven Tro's "Introductory Chemistry", Chapter 749

50. Practice—Write an Equation for the Reaction that Takes Place when an Aqueous Solution of ammonium sulfate is Mixed with an Aqueous Solution of lead (II) acetate. 50Tro's "Introductory Chemistry", Chapter 7

51. Ionic Equations  Equations that describe the chemicals put into the water and the product molecules are called molecular equations. 2 KOH(aq) + Mg(NO 3 ) 2 (aq)  2 KNO 3 (aq) + Mg(OH) 2 (s)  Equations that describe the actual dissolved species are called complete ionic equations. Aqueous electrolytes are written as ions. ○ Soluble salts, strong acids, strong bases. Insoluble substances and nonelectrolytes written in molecule form. ○ Solids, liquids, and gases are not dissolved, therefore, molecule form. 2K +1 (aq) + 2OH -1 (aq) + Mg +2 (aq) + 2NO 3 -1 (aq)  K +1 (aq) + 2NO 3 -1 (aq) + Mg(OH) 2(s) Tro's "Introductory Chemistry", Chapter 7 51

52. Writing Complete Ionic Equations  Rewrite the molecular equation, but dissociate strong electrolytes into individual ions. Strong electrolytes must be aqueous. ○ Solids, liquids, or gases cannot be electrolytes. All soluble ionic compounds are strong electrolytes. Strong acids are strong electrolytes. ○ HCl, HNO 3, H 2 SO 4.. ○ Weak acids are not written in the dissociated ion form. Molecular compounds do not have ions, leave in the molecular form. Tro's "Introductory Chemistry", Chapter 752

53. Ionic Equations  Ions that are both reactants and products are called spectator ions. 2K +1 (aq) + 2OH -1 (aq) + Mg +2 (aq) + 2NO 3 -1 (aq)  K +1 (aq) + 2NO 3 -1 (aq) + Mg(OH) 2(s) Tro's "Introductory Chemistry", Chapter 753 An ionic equation in which the spectator ions are removed is called a net ionic equation. 2OH -1 (aq) + Mg +2 (aq)  Mg(OH) 2(s)

54. Writing Net Ionic Equations  First, identify the spectator ions in the complete ionic equation. Identical ions on both sides of the equation.  Cancel out the spectator ions—the result is the net ionic equation. Tro's "Introductory Chemistry", Chapter 754

55. Summary  A molecular equation is a chemical equation showing the complete, neutral formulas for every compound in a reaction.  A complete ionic equation is a chemical equation showing all of the species as they are actually present in solution.  A net ionic equation is an equation showing only the species that actually participate in the reaction. Tro's "Introductory Chemistry", Chapter 755

56. Practice–Write the Ionic and Net Ionic Equation. K 2 SO 4 (aq) + Ba(NO 3 ) 2 (aq)  2 KNO 3 (aq) + BaSO 4 (s) Na 2 CO 3 (aq) + 2 HCl(aq)  2 NaCl(aq) + CO 2 (g) + H 2 O(l) Tro's "Introductory Chemistry", Chapter 756

57. Assignment  Problem Set #4 # 73,75, 76 Tro's "Introductory Chemistry", Chapter 757

58. Day Eight Tro's "Introductory Chemistry", Chapter 758

59. Properties of Acids  Sour taste  React with “active” metals, not noble metals I.e., Al, Zn, Fe, but not Cu, Ag or Au. Zn + 2 HCl  ZnCl 2 + H 2 Corrosive  React with carbonates, producing CO 2. Marble, baking soda, chalk, limestone. CaCO 3 + 2 HCl  CaCl 2 + CO 2 + H 2 O  React with bases to form ionic salts And often water Tro's "Introductory Chemistry", Chapter 759

60. Common Acids Tro's "Introductory Chemistry", Chapter 760

61. Properties of Bases  Taste bitter.  Feel slippery.  React with acids to form ionic salts. And often water. Neutralization. Tro's "Introductory Chemistry", Chapter 761

62. Common Bases Tro's "Introductory Chemistry", Chapter 762

63. Acid–Base Reactions  Also called neutralization reactions because the acid and base neutralize each other’s properties. acid + base  salt + water 2 HNO 3 (aq) + Ca(OH) 2 (aq)  Ca(NO 3 ) 2 (aq) + 2 H 2 O(l)  The net ionic equation for an acid-base reaction often is: H +1 (aq) + OH -1 (aq)  H 2 O(l) As long as the salt that forms is soluble in water. Tro's "Introductory Chemistry", Chapter 763

64. Process for Predicting the Products of an Acid–Base Reaction 1. Determine what ions each aqueous reactant has. 2. Exchange ions. (+) ion from one reactant with (-) ion from the other. H + combines with OH − to make water. 3. Balance charges of combined ions to get formula of the salt. 4. Balance the equation. Count atoms. 5. Determine solubility of the salt. Use the solubility rules. If the salt is insoluble or slightly soluble, it will precipitate. Tro's "Introductory Chemistry", Chapter 764

65. Example 7.11—Write the Molecular, Ionic, and Net- Ionic Equation for the Reaction of Aqueous Nitric Acid with Aqueous Calcium Hydroxide. Tro's "Introductory Chemistry", Chapter 765

66. Practice—Complete and Balance These Acid–Base Reactions. NH 4 OH(aq) + H 2 SO 4 (aq)  Al(OH) 3 (aq) + H 2 SO 3 (aq)  Ba(OH) 2 (aq) + H 2 SO 4 (aq)  Tro's "Introductory Chemistry", Chapter 766

67. Gas Evolution Reactions  Reactions in which the driving force is the production of a material that escapes as a gas are called gas evolution reactions.  Gases that you need to memorize: H 2 S, NH 3, SO 2, CO 2, NO 2, NO, H 2, N 2, O 2, F 2, Cl 2 Tro's "Introductory Chemistry", Chapter 767

68. Practice—Complete the Following Reactions. PbS(s) + H 2 SO 4 (aq)  Tro's "Introductory Chemistry", Chapter 768

69. Assignment  Problem Set #5 #81, 84, 85 Tro's "Introductory Chemistry", Chapter 769

70. Day Nine Tro's "Introductory Chemistry", Chapter 770

71. Other Patterns in Reactions  The precipitation, acid–base, and gas evolving reactions all involved exchanging the ions in the solution.  Other kinds of reactions involve transferring electrons from one atom to another. These are called oxidation–reduction reactions. Also known as redox reactions. Tro's "Introductory Chemistry", Chapter 771

72. Oxidation–Reduction Reactions  We say that the element that loses electrons in the reaction is oxidized.  And the substance that gains electrons in the reaction is reduced.  You cannot have one without the other Tro's "Introductory Chemistry", Chapter 772

73. Summary  Redox reactions occur when: A substance reacts with O 2. A metal combines with a nonmetal. In general, whenever electrons are transferred. Tro's "Introductory Chemistry", Chapter 773

74. Reactions of Metals with Nonmetals (Oxidation–Reduction)  Metals react with nonmetals to form ionic compounds. Ionic compounds are solids at room temperature.  The metal loses electrons and becomes a cation. The metal undergoes oxidation.  The nonmetal gains electrons and becomes an anion. The nonmetal undergoes reduction.  In the reaction, electrons are transferred from the metal to the nonmetal. 2 Na(s) + Cl 2 (g)  NaCl(s) Tro's "Introductory Chemistry", Chapter 774

75. Recognizing Redox Reactions  Any reaction where O 2 is a reactant or a product is a redox reaction.  Any reaction between a metal and a nonmetal is redox.  Any reaction where electrons are transferred is redox. When a free element gets combined into a compound, it will be either oxidized or reduced. N 2 (g) + H 2 (g)  NH 3 (g) When a metal cation changes its charge, it will be either oxidized if its charge increases or reduced if its charge decreases. CuCl(aq) + FeCl 3 (aq)  FeCl 2 (aq) + CuCl 2 (aq) Tro's "Introductory Chemistry", Chapter 775

76. Practice—Decide Whether Each of the Following Reactions Is a Redox Reaction. 2 Al(s) + 3 Br 2 (l)  2 AlBr 3 (s) CaSO 3 (s) + 2 HCl(aq)  CaCl 2 (aq) + SO 2 (g) + H 2 O(l) Fe 2 O 3 (s) + C(s)  2 Fe(s) + 3 CO(g) SO 2 (g) + O 2 (g) + H 2 O(l)  H 2 SO 4 (aq) Tro's "Introductory Chemistry", Chapter 776

77. Combustion Reactions  Reactions in which O 2 (g) is a reactant are called combustion reactions.  Combustion reactions release lots of energy. They are exothermic.  Combustion reactions are a subclass of oxidation– reduction reactions. Tro's "Introductory Chemistry", Chapter 777 2 C 8 H 18 (g) + 25 O 2 (g)  16 CO 2 (g) + 18 H 2 O(g)

78. Products of Combustion  When a material burns that contains carbon and hydrogen, the products are always CO 2 (g) and H 2 O(g). Tro's "Introductory Chemistry", Chapter 778

79. Practice—Write the Equation for Each Reaction.  Combustion of the anesthetic cyclopropane, C 3 H 6.  Combustion of the non-toxic antifreeze propylene glycol, C 3 H 8 O 2. Tro's "Introductory Chemistry", Chapter 779

80. Assignment  Problem Set #6 #87-89 Tro's "Introductory Chemistry", Chapter 780

81. Day Ten Tro's "Introductory Chemistry", Chapter 781

82. Classifying Reactions  One way is based on the process that happens. Precipitation, neutralization, formation of a gas, or transfer of electrons. 82

83. Classifying Reactions, Continued  Another scheme classifies reactions by what the atoms do. 83 Type of reactionGeneral equation Synthesis A + B  AB Decomposition AB  A + B Displacement A + BC  AC + B Double displacement AB + CD  AD + CB

84. Synthesis Reactions  Also known as composition or combination reactions.  Two (or more) reactants combine together to make one product. Simpler substances combining together. 2 CO + O 2  2 CO 2 2 Mg + O 2  2 MgO HgI 2 + 2 KI  K 2 HgI 4 Tro's "Introductory Chemistry", Chapter 784

85. Decomposition Reactions  A large molecule is broken apart into smaller molecules or its elements. Caused by addition of energy into the molecule.  Have only one reactant, make 2 or more products. Tro's "Introductory Chemistry", Chapter 785

86. Single Displacement Reactions  Reactions that involve one atom displacing another and replacing it in a compound.  Other examples of displacement reactions are: Fe 2 O 3 (s) + Al(s)  Fe(s) + Al 2 O 3 (s) 2 Na(s) + 2 H 2 O(aq)  2 NaOH(aq) + H 2 (g) Tro's "Introductory Chemistry", Chapter 786

87. Double Displacement Reactions  Two ionic compounds exchange ions.  X  Y  (aq) + A  B  (aq)  XB + AY  Precipitation, acid–base, and gas evolving reactions are also double displacement reactions. Tro's "Introductory Chemistry", Chapter 787

88. Practice—Classify the Following Reactions as Synthesis, Decomposition, Single Displacement, or Double Displacement. 3 Mg(s) + 2 FeCl 3 (aq)  3 MgCl 2 (aq) + 2 Fe(s) CO 2 (g) + H 2 O(l)  H 2 CO 3 (aq) 3 KOH(aq) + H 3 PO 4 (aq)  K 3 PO 4 (aq) + 3 H 2 O(l) Tro's "Introductory Chemistry", Chapter 788

89. Assignment  Review Sheet Tro's "Introductory Chemistry", Chapter 789