1. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry, 3 rd Edition Nivaldo Tro Chapter 7 Chemical Reactions 2009, Prentice Hall

2. Tro's "Introductory Chemistry", Chapter 7 2 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.

3. Tro's "Introductory Chemistry", Chapter 7 3 Evidence of Chemical Change Color Change Formation of Solid Precipitate Formation of a Gas Emission of Light Release or Absorption of Heat

4. Tro's "Introductory Chemistry", Chapter 7 4 Evidence of Chemical Change, Continued In order to be absolutely sure that a chemical reaction has taken place, you need to go down to the molecular level and analyze the structures of the molecules at the beginning and end. Is boiling water a chemical change?

5. Tro's "Introductory Chemistry", Chapter 7 5 Practice—Decide Whether Each of the Following Involve a Chemical Reaction. Photosynthesis Heating sugar until it turns black Heating ice until it turns liquid Digestion of food Dissolving sugar in water Burning of alcohol in a flambé dessert 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 Yes, alcohol combining with O 2 to make CO 2 and H 2 O

6. Tro's "Introductory Chemistry", Chapter 7 6 Conservation of Mass Matter cannot be created or destroyed. Therefore, the total mass cannot change. And the total mass of the reactants will be the same as the total mass of the 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.

7. Tro's "Introductory Chemistry", Chapter 7 7 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. CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g)

8. Tro's "Introductory Chemistry", Chapter 7 8 Chemical Equations, Continued This equation is balanced, meaning that there are equal numbers of atoms of each element on the reactant and product sides. To obtain the number of atoms of an element, multiply the subscript by the coefficient. 1  C  1 4  H  4 4  O  2 + 2 CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g)

9. Tro's "Introductory Chemistry", Chapter 7 9 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.

10. Tro's "Introductory Chemistry", Chapter 7 10 Writing Balanced Chemical Equations 1.Write a skeletal equation by writing the formula of each reactant and product. 2.Count the number of atoms of each element on each side of the equation. Polyatomic ions may often be counted as if they are one “element”. 3.Pick an element to balance. If an element is found in only one compound on both sides, balance it first.  Metals before nonmetals. Leave elements that are free elements somewhere in the equation until last.  Balance free elements by adjusting the coefficient where it is a free element.

11. Tro's "Introductory Chemistry", Chapter 7 11 Practice #1 When aluminum metal reacts with air, it produces a white, powdery compound called aluminum oxide. Reacting with air means reacting with O 2 : Aluminum(s) + oxygen(g)  aluminum oxide(s) Al(s) + O 2 (g)  Al 2 O 3 (s)

12. Tro's "Introductory Chemistry", Chapter 7 12 Practice #1, Continued When aluminum metal reacts with air, it produces a white, powdery compound called aluminum oxide. Reacting with air means reacting with O 2 : Aluminum(s) + oxygen(g)  aluminum oxide(s) Al(s) + O 2 (g)  Al 2 O 3 (s) 4 Al(s) + 3 O 2 (g)  2 Al 2 O 3 (s)

13. Tro's "Introductory Chemistry", Chapter 7 13 Practice #2 Combustion of ethyl alcohol (C 2 H 5 OH) in flambé (a brandied flaming dessert). Combustion is burning, and therefore, reacts with O 2. Combustion of compounds containing C and H always make CO 2 (g) and H 2 O(g) as products. C 2 H 5 OH(l) + O 2 (g)  CO 2 (g) + H 2 O(g)

14. Tro's "Introductory Chemistry", Chapter 7 14 Practice #2, Continued Combustion of ethyl alcohol (C 2 H 5 OH) in flambé (a brandied flaming dessert). Combustion is burning, and therefore, reacts with O 2. Combustion of compounds containing C and H always make CO 2 (g) and H 2 O(g) as products. C 2 H 5 OH(l) + O 2 (g)  CO 2 (g) + H 2 O(g) C 2 H 5 OH(l) + 3 O 2 (g)  2 CO 2 (g) + 3 H 2 O(g)

15. Tro's "Introductory Chemistry", Chapter 7 15 Practice #3 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)

16. Tro's "Introductory Chemistry", Chapter 7 16 Practice #3, Continued 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) 2 C 4 H 10 (l) + 13 O 2 (g)  8 CO 2 (g) + 10 H 2 O(g)

17. Tro's "Introductory Chemistry", Chapter 7 17 Aqueous Solutions Many times, the chemicals we are reacting together are 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.

18. Tro's "Introductory Chemistry", Chapter 7 18 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.

19. Tro's "Introductory Chemistry", Chapter 7 19 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) K +1 I -1 K I Cu +2 SO 4 -2 Cu SO 4

20. Tro's "Introductory Chemistry", Chapter 7 20 Electrolytes Electrolytes are substances whose water solution is a conductor of electricity. All electrolytes have ions dissolved in water.

21. Tro's "Introductory Chemistry", Chapter 7 21 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.

22. Tro's "Introductory Chemistry", Chapter 7 22 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.

23. Tro's "Introductory Chemistry", Chapter 7 23 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.

24. Tro's "Introductory Chemistry", Chapter 7 24 When Will a Salt Dissolve?, Continued Predicting whether a compound will dissolve in water is not easy. The best way to do it is to do some experiments to test whether a compound will dissolve in water, then develop some rules based on those experimental results. We call this method the empirical method.

25. Tro's "Introductory Chemistry", Chapter 7 25 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+, Cu + SO 4 2– Ca 2+, Sr 2+, Ba 2+, Pb 2+, Ag +, Ra 2+ Solubility Rules: Compounds that Are Generally Soluble in Water

26. Tro's "Introductory Chemistry", Chapter 7 26 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–, SO 3 2– Li +, Na +, K +, NH 4 + Solubility Rules: Compounds that Are Generally Insoluble

27. Tro's "Introductory Chemistry", Chapter 7 27 Using the Solubility Rules to Predict an Ionic Compound’s Solubility in Water First check the cation: If it is Li +, Na +, K +, or NH 4 +, then the compound will be soluble in water. Regardless of the anion. If the cation is not Li +, Na +, K +, or NH 4 +, then follow the rule for the anion. If a rule says the compounds are mostly soluble, then the exceptions are insoluble. If a rule says the compounds are mostly insoluble, then the exceptions are soluble. Note: slightly soluble  insoluble.

28. Tro's "Introductory Chemistry", Chapter 7 28 Determine if Each of the Following Is Soluble in Water KOH AgBr CaCl 2 Pb(NO 3 ) 2 PbSO 4

29. Tro's "Introductory Chemistry", Chapter 7 29 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.

30. Tro's "Introductory Chemistry", Chapter 7 30 Precipitation Reactions Many reactions are done by mixing aqueous solutions of electrolytes together. When this is done, often a reaction will take place from the cations and anions in the two solutions that are exchanging. If the ion exchange results in forming a compound that is insoluble in water, it will come out of solution as a precipitate.

31. Tro's "Introductory Chemistry", Chapter 7 31 Precipitation Reactions, Continued 2 KI(aq) + Pb(NO 3 ) 2 (aq)  2 KNO 3 (aq) + PbI 2 (s)

32. Tro's "Introductory Chemistry", Chapter 7 32 Precipitation Reactions, Continued 2 KI(aq) + Pb(NO 3 ) 2 (aq)  2 KNO 3 (aq) + PbI 2 (s)

33. Tro's "Introductory Chemistry", Chapter 7 33 No Precipitate Formation = No Reaction KI(aq) + NaCl(aq)  KCl(aq) + NaI(aq) All ions still present,  no reaction.

34. Tro's "Introductory Chemistry", Chapter 7 34 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.

35. Tro's "Introductory Chemistry", Chapter 7 35 Practice–Predict the Products and Balance the Equation KCl(aq) + AgNO 3 (aq)  Na 2 S(aq) + CaCl 2 (aq) 

36. Tro's "Introductory Chemistry", Chapter 7 36 KCl(aq) + AgNO 3 (aq)  KCl(aq) + AgNO 3 (aq)  KNO 3 (aq) + AgCl(s) Na 2 S(aq) + CaCl 2 (aq)  Na 2 S(aq) + CaCl 2 (aq)  2 NaCl(aq) + CaS(aq) No reaction. Practice–Predict the Products and Balance the Equation, Continued

37. Tro's "Introductory Chemistry", Chapter 7 37 Practice—Write an Equation for the Reaction that Takes Place when an Aqueous Solution of (NH 4 ) 2 SO 4 is Mixed with an Aqueous Solution of Pb(C 2 H 3 O 2 ) 2.

38. Tro's "Introductory Chemistry", Chapter 7 38 Practice—Write an Equation for the Reaction that Takes Place when an Aqueous Solution of (NH 4 ) 2 SO 4 is Mixed with an Aqueous Solution of Pb(C 2 H 3 O 2 ) 2, Continued. (NH 4 ) 2 SO 4 (aq) + Pb(C 2 H 3 O 2 ) 2 (aq)  2 NH 4 C 2 H 3 O 2 (aq) + PbSO 4 (s)

39. Tro's "Introductory Chemistry", Chapter 7 39 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)

40. Tro's "Introductory Chemistry", Chapter 7 40 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.

41. Tro's "Introductory Chemistry", Chapter 7 41 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) 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)

42. Tro's "Introductory Chemistry", Chapter 7 42 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.

43. Tro's "Introductory Chemistry", Chapter 7 43 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.

44. Tro's "Introductory Chemistry", Chapter 7 44 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)

45. Tro's "Introductory Chemistry", Chapter 7 45 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) 2K + (aq) + SO 4 2− (aq) + Ba 2+ (aq) + 2NO 3 − (aq)  2K + (aq) + 2NO 3 − (aq) + BaSO 4 (s) Ba 2+ (aq) + SO 4 -2 (aq)  BaSO 4 (s) Na 2 CO 3 (aq) + 2 HCl(aq)  2 NaCl(aq) + CO 2 (g) + H 2 O(l) 2Na + (aq) + CO 3 2− (aq) + 2H + (aq) + 2 Cl − (aq)  2Na + (aq) + 2Cl − (aq) + CO 2 (g) + H 2 O(l) CO 3 -2 (aq) + 2 H +1 (aq)  CO 2 (g) + H 2 O(l)

46. Tro's "Introductory Chemistry", Chapter 7 46 Properties of Acids Sour taste. Change color of vegetable dyes. 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.

47. Tro's "Introductory Chemistry", Chapter 7 47 Common Acids

48. Tro's "Introductory Chemistry", Chapter 7 48 Properties of Bases A.k.a. alkalis. Taste bitter. Feel slippery. Change color of vegetable dyes. Different color than acid. Litmus = blue. React with acids to form ionic salts. And often water. Neutralization.

49. Tro's "Introductory Chemistry", Chapter 7 49 Common Bases

50. Tro's "Introductory Chemistry", Chapter 7 50 Acid–Base Reactions Also called neutralization reactions because the acid and base neutralize each other’s properties. In the reaction of an acid with a base, the H +1 from the acid combines with the OH -1 from the base to make water. The cation from the base combines with the anion from the acid to make the salt. 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.

51. Tro's "Introductory Chemistry", Chapter 7 51 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.

52. Tro's "Introductory Chemistry", Chapter 7 52 Example 7.11—Write the Molecular, Ionic, and Net- Ionic Equation for the Reaction of Aqueous Nitric Acid with Aqueous Calcium Hydroxide, Continued. 6.Dissociate all strong electrolytes to get complete ionic equation. HNO 3 is a strong acid, Ca(OH) 2 and Ca(NO 3 ) 2 are ionic. Not H 2 O. 2H + (aq) + 2NO 3 − (aq) + Ca 2+ (aq) + 2OH − (aq)  Ca 2+ (aq) + 2NO 3 − (aq) + H 2 O(l) 7.Eliminate spectator ions to get net-ionic equation. 2 H + (aq) + 2 OH − (aq)  H 2 O(l) H + (aq) + OH − (aq)  H 2 O(l)

53. Tro's "Introductory Chemistry", Chapter 7 53 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) 

54. Tro's "Introductory Chemistry", Chapter 7 54 Practice—Complete and Balance These Acid–Base Reactions, Continued. 2 NH 4 OH(aq) + H 2 SO 4 (aq)  (NH 4 ) 2 SO 4 (aq) + 2 H 2 O(l) 2 Al(OH) 3 (aq) + 3 H 2 SO 3 (aq)  Al 2 (SO 3 ) 3 (s) + 6 H 2 O(l) Ba(OH) 2 (aq) + H 2 SO 4 (aq)  BaSO 4 (s) + 2 H 2 O(l)

55. Tro's "Introductory Chemistry", Chapter 7 55 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. Some reactions form a gas directly from the ion exchange. K 2 S(aq) + H 2 SO 4 (aq)  K 2 SO 4 (aq) + H 2 S(g) Other reactions form a gas by the decomposition of one of the ion exchange products into a gas and water. K 2 SO 3 (aq) + H 2 SO 4 (aq)  K 2 SO 4 (aq) + H 2 SO 3 (aq) H 2 SO 3  H 2 O(l) + SO 2 (g)

56. Tro's "Introductory Chemistry", Chapter 7 56 Compounds that Undergo Gas Evolving Reactions Reactant type Reacting with Ion exchange product Decom- pose? Gas formed Example Metal n S, metal HS AcidH2SH2SNoH2SH2S K 2 S(aq) + 2HCl(aq)  2KCl(aq) + H 2 S(g) Metal n CO 3, metal HCO 3 AcidH 2 CO 3 YesCO 2 K 2 CO 3 (aq) + 2HCl(aq)  2KCl(aq) + CO 2 (g) + H 2 O(l) Metal n SO 3 metal HSO 3 AcidH 2 SO 3 YesSO 2 K 2 SO 3 (aq) + 2HCl(aq)  2KCl(aq) + SO 2 (g) + H 2 O(l) (NH 4 ) n anionBaseNH 4 OHYesNH 3 KOH(aq) + NH 4 Cl(aq)  KCl(aq) + NH 3 (g) + H 2 O(l)

57. Tro's "Introductory Chemistry", Chapter 7 57 Practice—Complete the Following Reactions. PbS(s) + H 2 SO 4 (aq)  HNO 3 (aq) + NaHCO 3 (aq) 

58. Tro's "Introductory Chemistry", Chapter 7 58 Practice—Complete the Following Reactions, Continued. PbS(s) + H 2 SO 4 (aq)  PbSO 4 (s) + H 2 S(g) HNO 3 (aq) + NaHCO 3 (aq)  NaNO 3 (aq) + CO 2 (g) + H 2 O(l)

59. Tro's "Introductory Chemistry", Chapter 7 59 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. 2 C 8 H 18 (g) + 25 O 2 (g)  16 CO 2 (g) + 18 H 2 O(g)

60. Tro's "Introductory Chemistry", Chapter 7 60 Products of Combustion When a material burns that contains carbon and hydrogen, the products are always CO 2 (g) and H 2 O(g). The reaction for the combustion of ethylene, C 2 H 4 (g) is: C 2 H 4 (g) + 3 O 2 (g)  2 CO 2 (g) + 2 H 2 O(g) The reaction for the combustion of ethylene glycol, C 2 H 6 O 2 (g) is: 2 C 2 H 6 O 2 (g) + 5 O 2 (g)  4 CO 2 (g) + 6 H 2 O(g)

61. Tro's "Introductory Chemistry", Chapter 7 61 Combustion Products To predict the products of a combustion reaction, combine each element in the other reactant with oxygen. ReactantCombustion product Contains CCO 2 (g) Contains HH 2 O(g) Contains SSO 2 (g) Contains NNO(g) or NO 2 (g) Contains metalM 2 O n (s)

62. Tro's "Introductory Chemistry", Chapter 7 62 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.

63. Tro's "Introductory Chemistry", Chapter 7 63 Practice—Write the Equation for Each Reaction, Continued. Combustion of the anesthetic cyclopropane, C 3 H 6 (g). 2 C 3 H 6 (g) + 9 O 2 (g)  6 CO 2 (g) + 6 H 2 O(g) Combustion of the non-toxic antifreeze propylene glycol, C 3 H 8 O 2 (l). 2 C 3 H 6 O 2 (l) + 7 O 2 (g)  6 CO 2 (g) + 6 H 2 O(g)

64. 64 Classifying Reactions, Continued Another scheme classifies reactions by what the atoms do. Type of reactionGeneral equation Synthesis A + B  AB Decomposition AB  A + B Displacement A + BC  AC + B Double displacement AB + CD  AD + CB

65. Tro's "Introductory Chemistry", Chapter 7 65 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

66. Tro's "Introductory Chemistry", Chapter 7 66 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.

67. Tro's "Introductory Chemistry", Chapter 7 67 Decomposition of Water

68. Tro's "Introductory Chemistry", Chapter 7 68 Single Displacement Reactions Reactions that involve one atom displacing another and replacing it in a compound. In the reaction Zn(s) + 2 HCl(aq)  ZnCl 2 (aq) + H 2 (g), the atom Zn displaces H from the 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)

69. Tro's "Introductory Chemistry", Chapter 7 69 Displacement of Copper by Zinc

70. Tro's "Introductory Chemistry", Chapter 7 70 Double Displacement Reactions Two ionic compounds exchange ions. May be followed by decomposition of one of the products to make a gas. X  Y  (aq) + A  B  (aq)  XB + AY Precipitation, acid–base, and gas evolving reactions are also double displacement reactions.

71. Tro's "Introductory Chemistry", Chapter 7 71 Examples of Double Displacement CaCl 2 (aq) + Na 2 CO 3 (aq)  CaCO 3 (s) + 2 NaCl(aq) Ba(OH) 2 (s) + 2 HNO 3 (aq)  Ba(NO 3 ) 2 (aq) + 2 H 2 O(l) Li 2 CO 3 (aq) + 2 HCl(aq)  2 LiCl(aq) + CO 2 (g) + H 2 O(l)

72. Tro's "Introductory Chemistry", Chapter 7 72 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)

73. Tro's "Introductory Chemistry", Chapter 7 73 Practice—Classify the Following Reactions as Synthesis, Decomposition, Single Displacement, or Double Displacement, Continued. 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) Single displacement. Double displacement. Decomposition. Synthesis.