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Chapter 8 – Chemical Equations and Reactions

Chapter 8 – Chemical Equations and Reactions. Chemical Equations. A chemical equation represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction. Reactants – Starting substances on the left side of the equation

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Chapter 8 – Chemical Equations and Reactions

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  1. Chapter 8 – Chemical Equations and Reactions Honors Chemistry, Chapter 8 Page 1

  2. Chemical Equations • A chemical equation represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction. • Reactants – Starting substances on the left side of the equation • Products – Final substances on the right side of the equation • Obeys the Law of Conservation of Mass Honors Chemistry, Chapter 8 Page 2

  3. Indications of a Chemical Reaction • Evolution of heat and light. (Examples: Decomposition of ammonium dichromate, burning of methane.) • Production of a gas. (Example: Carbon dioxide released when baking soda and vinegar react.) Honors Chemistry, Chapter 8 Page 3

  4. Indications of a Chemical Reaction • Formation of a precipitate. (Example: Reaction of ammonium sulfide and cadmium nitrate  Yellow ppt.) • Color Change. (Example: When iron and water react the iron changes from metallic color to red/brown.) Honors Chemistry, Chapter 8 Page 4

  5. Characteristics of Chemical Equations • The equation must represent the known facts (all reactants and products must be identified by chemical analysis.) • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied. (Coefficients added as necessary. Coefficient: a small whole number in front of a formula in a chemical equation.) Honors Chemistry, Chapter 8 Page 5

  6. Elements That Normally Appear as Diatomic or Polyatomic Molecules Honors Chemistry, Chapter 8 Page 6

  7. Elements That Normally Appear as Diatomic or Polyatomic Molecules Honors Chemistry, Chapter 8 Page 7

  8. Word Equations • Word equation: An equation in which the reactants and products of a chemical reaction are represented by words. Methane + oxygen  carbon dioxide + Water • Arrow ( ) is read as: “react to yield”, “yield”, “produce”, or “form” Honors Chemistry, Chapter 8 Page 8

  9. Formula Equations • Formula equation: An equation which represents the reactants and products of a chemical reaction by their symbols or formulas. • CH4(g) + O2(g)  CO2 (g) + H2O(g) (not balanced) • CH4(g) + O2(g)  CO2 (g) + 2H2O(g) (partially balanced) • CH4(g) + 2O2(g)  CO2 (g) + 2H2O(g) (balanced) Honors Chemistry, Chapter 8 Page 9

  10. Symbols Used in Chemical Equations Honors Chemistry, Chapter 8 Page 10

  11. Symbols Used in Chemical Equations Honors Chemistry, Chapter 8 Page 11

  12. Reaction Symbol Definitions • Catalyst: A catalyst is a substance that changes the rate of a chemical reaction but can be recovered unchanged. • Reversable Reaction: A chemical reaction in which the products re-form the original reactants. Honors Chemistry, Chapter 8 Page 12

  13. Practice Writing Formulas Barium Acetate Ammonium Sulfate Aluminum Carbonate Iron (III) Chromate Nickel (II) Hydroxide Copper (II) Nitrate Rubidium Chloride Lithium Permanganate Strontium Peroxide Calcium Phosphate Mercury (I) Sulfate Magnesium Bromide Zinc ThiosulfateTin (IV) Chlorate Honors Chemistry, Chapter 8 Page 13

  14. Example Reactions 3Fe(s) + 4 H2O(g) Fe3O4 + 4 H2(g) 2HgO(s) 2Hg(l) + O2(g) C2H4(g) + H2(g) C2H6(g) D Pressure Pt Honors Chemistry, Chapter 8 Page 14

  15. Significance of a Chemical Equation • The coefficients of a chemical reaction indicate relative, not absolute amounts of reactants and products. H2(g) + Cl2(g)  2HCl(g) In other words: 1 molecule H2 : 1 molecule Cl2 : 2 molecules HCl Or 1 mole H2 : 1 mole Cl2 : 2 mole HCl Honors Chemistry, Chapter 8 Page 15

  16. Significance of a Chemical Equation • The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients. • 1 mol H2 x 2.02 g H2/mol H2 = 2.02 g H2 • 1 mol Cl2 x 70.90 g Cl2/mol Cl2 = 70.90 g Cl2 • 2 mol HCl x 36.46 g HCl/mol HCl = 72.92 g HCl Honors Chemistry, Chapter 8 Page 16

  17. Significance of a Chemical Equation • The reverse for a chemical reaction has the same relative amounts of substances as the forward reaction. Honors Chemistry, Chapter 8 Page 17

  18. Balancing Chemical Equations • Identify the names of the reactants and the products and write the word equation. Water  hydrogen + oxygen • Write a formula equation by substituting correct formulas for the names of the reactants and the products. H2O(l)  H2(g) + O2(g) (not balanced) Honors Chemistry, Chapter 8 Page 18

  19. Balancing Chemical Equations • Balance the equation according to the law of conservation of mass • Balance different types of atoms one at a time. • First balance the atoms of elements that are combined and that appear only once on each side of the equation. • Balance polyatomic ions that appear on both sides of the equation as single units. • Balance H atoms and O atoms after all other elements are balanced. • 2H2O(l)  H2(g) + O2(g) (Partially balanced) • 2H2O(l)  2H2(g) + O2(g) (balanced) Honors Chemistry, Chapter 8 Page 19

  20. Balancing Chemical Equations • Count atoms to be sure the equation is balanced. • 2H2O(l)  2H2(g) + O2(g) (balanced) • (4H + 2O) = (4H) + (2O) Honors Chemistry, Chapter 8 Page 20

  21. When Balancing . . . • Always write the correct formulas for both the reactants and the products • Never try to balance an equation by changing subscripts(!) Honors Chemistry, Chapter 8 Page 21

  22. Balancing Exercise #1 Using the four steps, write a balanced chemical equation for the reaction between zinc and aqueous hydrochloric acid which produces zinc chloride and hydrogen gas. Honors Chemistry, Chapter 8 Page 22

  23. Exercise #1 - Solution • zinc + hydrochloric acid  zinc chloride + Hydrogen • Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g) • Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) • (1 Zn)+(2H + 2Cl) = (1Zn+2Cl) + (2H) Honors Chemistry, Chapter 8 Page 23

  24. Balancing Exercise #2 Using the four steps, write a balanced chemical equation for the reaction between aluminum carbide (Al4C3) and water which produces methane gas (CH4) and aluminum hydroxide. Honors Chemistry, Chapter 8 Page 24

  25. Exercise #2 - Solution • aluminum carbide + water  methane + aluminum hydroxide • Al4C3(s) + H2O(l)  CH4(g) + Al(OH)3(s) • Al4C3(s)+12H2O(l)3CH4(g)+4Al(OH)3(s) • (4Al+3C)+(24H+12O) • = (3C+12H) + (4Al+12O+12H) Honors Chemistry, Chapter 8 Page 25

  26. Balancing Exercise #3 Using the four steps, write a balanced chemical equation for the reaction between calcium carbide (CaC2) and water which produces ethyne gas (HCCH) (also known as acetylene) and calcium hydroxide. Honors Chemistry, Chapter 8 Page 26

  27. Exercise #3 - Solution • calcium carbide + water  ethyne + calcium hydroxide • CaC2(s)+H2O(l)  HCCH(g)+Ca(OH)2(s) • CaC2(s)+2H2O(l)  HCCH(g)+Ca(OH)2(s) • (1Ca+2C)+(4H+2O) • = (2H + 2C) + (1Ca+2O+2H) Honors Chemistry, Chapter 8 Page 27

  28. Chapter 8, Section 1 Review • List four observations that indicate that a chemical reaction has taken place. • List three requirements for a correctly written chemical equation. • Write a word equation and a formula equation for a given chemical reaction. • Balance a formula equation by inspection. Honors Chemistry, Chapter 8 Page 28

  29. Broad Types of Chemical Reactions • Synthesis: A + X AX • Decomposition: AX  A + X • Single-Replacement: A + BX  AX + B or Y + BX  BY + X • Double-Replacement: AX + BY AY + BX • Combustion: 2A + O2  2AO (coefficients and subscripts may vary) Honors Chemistry, Chapter 8 Page 29

  30. Synthesis Reactions • In a synthesis reaction, also known as a composition reaction, two or more substances combine to form a new compound. • A + X AX • Three Types • Elements + Oxygen or Sulfur • Metals with Halogens • Reactions with Oxides Honors Chemistry, Chapter 8 Page 30

  31. Reactions of Elements with Oxygen or Sulfur • Mg(s) + O2(g)  ? 2Mg(s) + O2(g) 2MgO(s) • Rb(s) + S8(s)  ? 16Rb(s)+S8(s) 8Rb2S(s) • Fe(s) + O2(g)  ? 2Fe(s) + O2  2FeO 4Fe(s) + 3O2  2Fe2O3 Honors Chemistry, Chapter 8 Page 31

  32. Reactions of Elements with Oxygen or Sulfur • C(s) + O2(g)  ? C(s) + O2(g)  CO2(g) 2C(s) + O2(g) 2CO(g) • S8(s) + O2  ? S8(s) + 8O2 8 SO2(g) • H2(g) + O2(g)  ? 2H2(g) + O2(g) 2H2O(g) Honors Chemistry, Chapter 8 Page 32

  33. Reactions of Metals with Halogens • Na(s) + Cl2(g)  ? 2Na(s) + Cl2(g)  2NaCl(s) • K(s) + I2(s)  ? 2K(s) + I2(s)  2KI(s) • Mg(s) + F2(g)  ? Mg(s) + F2(g)  MgF2(s) • Sr(s) + Br2(l)  ? Sr(s) + Br2(l)  SrBr2(s) Honors Chemistry, Chapter 8 Page 33

  34. Reactions of Metals with Halogens • Na(s) + F2(g)  ? 2Na(s) + F2(g)  2NaF(s) • Co(s) + F2(g)  ? 2Co(s) + 3F2(g)  2CoF3(s) • U(s) + F2(g)  ? (Hint: Uranium (VI)) U(s) + 3F2(g)  UF6(g) Honors Chemistry, Chapter 8 Page 34

  35. Synthesis Reactions with Oxides • CaO(s) + H2O(l)  ? CaO(s)+H2O(l)Ca(OH)2(s) • SO2(g) + H2O(l)  ? SO2(g)+H2O(l)  H2SO3(aq) • H2SO3(aq) + O2(g)  ? 2H2SO3(aq) + O2(g)  2H2SO4(aq) • CaO(s) + SO2(g)  ? CaO(s)+ SO2(g)  CaSO3(s) Honors Chemistry, Chapter 8 Page 35

  36. Decomposition Reactions • In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. • AX A + X • Five Types • Decomposition of Binary Compounds • Decomposition of Metal Carbonates • Decomposition of Metal Hydroxides • Decomposition of Metal Chlorates • Decomposition of Acids Honors Chemistry, Chapter 8 Page 36

  37. Decomposition of Binary Compounds • H2O(l) electricity ? 2H2O(l)electricity 2H2(g) + O2(g) (electrolysis) • HgO(s) D ? 2 HgO(s) D 2 Hg(l) + O2(g) (thermolysis) Honors Chemistry, Chapter 8 Page 37

  38. Decompostion of Metal Carbonates CaCO3(s) D ? CaCO3D CaO(s) + CO2(g) • Decomposition of Metal Hydroxides Ca(OH)2(s) D ? Ca(OH)2(s) D CaO(s)+H2O(g) Honors Chemistry, Chapter 8 Page 38

  39. Decompostion of Metal Chlorates • KClO3(s) D ? 2KClO3(s) D 2KCl(s)+3O2(g) • Decomposition of Acids • H2CO3(aq)  ? H2CO3(aq)  CO2(g)+H2O(l) • H2SO4(aq) D ? H2SO4(aq) D SO3(g)+H2O(l) • (Sulfurous Acid  ?) Honors Chemistry, Chapter 8 Page 39

  40. Single-Replacement Reactions • In a single-replacement reaction, also known as a displacement reaction, one element replaces a similar element in a compound. • A + BX AX + B or • Y + BX  BY + X • Four Types • Replacement of a Metal by Another Metal • Replacement of H2 in Water by a Metal • Replacement of H2 in an Acid by a Metal • Replacement of Halogens Honors Chemistry, Chapter 8 Page 40

  41. Replacement of a Metal with another Metal • Al(s) + Pb(NO3)2(aq)  ? 2Al(s)+3Pb(NO3)2(aq)3Pb(s)+2Al(NO3)3 • Replacement of H2 in Water by a Metal • Na(s) + H2O(l)  ? 2Na(s)+ 2H2O(l)  2NaOH(aq) + H2(g) • Fe(s) + H2O(g)  ? 3Fe(s)+ 4H2O(g)  Fe3O4(s)+ 4H2(g) • (Oxidation State of Fe?) Honors Chemistry, Chapter 8 Page 41

  42. Replacement of H2 in an Acid by a Metal • Mg(s) + HCl(aq)  ? • Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g) • Replacement of Halogens • Cl2(g) + 2KBr(aq)  2KCl(aq) + Br2(l) • F2(g) + 2NaCl(aq)  2NaF(aq) + Cl2(g) • Br2(l) + KCl(aq)  no reaction Honors Chemistry, Chapter 8 Page 42

  43. Double-Replacement Reactions • In double-replacement reactions, the ions of two compounds exchange places to make two new compounds. • AX + BY AY + BX • Three Types • Formation of a Precipitate • Formation of a Gas • Formation of Water Honors Chemistry, Chapter 8 Page 43

  44. Formation of a Precipitate • KI(aq) + Pb(NO3)2(aq)  ? • 2KI(aq)+Pb(NO3)2(aq)PbI2(s)+ 2KNO3(aq) • Formation of a Gas • FeS(s) + 2HCl(aq)  H2S(g) + FeCl2(aq) • Formation of Water (acid-base reactions) • HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Honors Chemistry, Chapter 8 Page 44

  45. Combustion Reactions • In a combustion reaction, a substance combines with oxygen, releasing a large amount of energy in the form of light and heat. • 2H2(g) + O2(g)  2H2O(g) • C3H8(g) + 5O2  3CO2(g) + 4H2O(g) Honors Chemistry, Chapter 8 Page 45

  46. Chapter 8, Section 2 Review • Define and give general equations for: • Synthesis reactions • Decomposition reactions • Single-replacement reactions • Double-replacement reactions • Combustion reactions • Classify a reaction into one of the five categories above. Honors Chemistry, Chapter 8 Page 46

  47. Chapter 8, Section 2 Review continued • List three types of synthesis reactions and five types of decomposition reactions. • List four types of single replacement reactions and three types of double replacement reactions. • Predict the products of simple reactions given the reactants. Honors Chemistry, Chapter 8 Page 47

  48. Activity Series • An Activity series is a list of elements organized according to the ease with which the elements undergo certain chemical reactions. • Each element in the series will replace all elements below it in the series in a single-replacement reaction. Honors Chemistry, Chapter 8 Page 48

  49. Activity Series of Metals Honors Chemistry, Chapter 8 Page 49

  50. Activity Series of Halogens Fluorine Chlorine Bromine Iodine Honors Chemistry, Chapter 8 Page 50

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