1. Chemistry Chapter 8: Chemical Equations and Reactions

2. Chemical reaction The process by which one or more substances are changed into one or more different substancesThe process by which one or more substances are changed into one or more different substances Reactants: original substancesReactants: original substances They reactThey react Products: resulting substancesProducts: resulting substances They are producedThey are produced 2Chemistry Chapter 8

3. Indications of a chemical reaction 1.Formation of a precipitate Solid produced when two liquids are mixedSolid produced when two liquids are mixed 2.Gas is produced Foaming or bubblesFoaming or bubbles 3.Energy is released Heat and light and/or sound are producedHeat and light and/or sound are produced 4.Color change 3Chemistry Chapter 8

4. Chemical equation Represents a chemical reaction with symbols and formulasRepresents a chemical reaction with symbols and formulas Shows the relative amounts of products and reactantsShows the relative amounts of products and reactants 4Chemistry Chapter 8

5. Chemical equations 1.Must represent known facts All reactants and products must be identifiedAll reactants and products must be identified 2.Must contain the correct formulas for reactants and products Pure elements are represented with their symbolsPure elements are represented with their symbols Sulfur is S 8 and phosphorus is P 4Sulfur is S 8 and phosphorus is P 4 Some are diatomicSome are diatomic 5Chemistry Chapter 8

6. Diatomic molecules The magnificent sevenThe magnificent seven See table 8-1 on page 243See table 8-1 on page 243 There are 7 of themThere are 7 of them On the periodic table, they make a 7 (plus hydrogen)On the periodic table, they make a 7 (plus hydrogen)On the periodic table, they make a 7 (plus hydrogen)On the periodic table, they make a 7 (plus hydrogen) 6Chemistry Chapter 8

7. Chemical equations 3.Law of conservation of mass must be satisfied Same number of atoms of each element on both sides of the equationSame number of atoms of each element on both sides of the equation Sometimes coefficients are neededSometimes coefficients are needed Small whole number in front of a chemical formulaSmall whole number in front of a chemical formula 7Chemistry Chapter 8

8. Word equation Zinc + hydrochloric acid  hydrogen + zinc chloride Zinc + hydrochloric acid  hydrogen + zinc chloride Qualitative, not quantitativeQualitative, not quantitative Read the arrow as “react to yield”, “yield”, “produce”, or “form”Read the arrow as “react to yield”, “yield”, “produce”, or “form” 8Chemistry Chapter 8

9. Formula equation Represents the reactants and products by their symbols or formulasRepresents the reactants and products by their symbols or formulas Zn(s) + HCl(aq)  H 2 (g) + ZnCl 2 (aq)Zn(s) + HCl(aq)  H 2 (g) + ZnCl 2 (aq) (s) means solid(s) means solid (aq) means aqueous – dissolved in water(aq) means aqueous – dissolved in water (g) means gaseous(g) means gaseous (l) means liquid(l) means liquid 9Chemistry Chapter 8

10. Balancing equations We need to have the same number of atoms of each element on both sides of the equation.We need to have the same number of atoms of each element on both sides of the equation. Add coefficients to make this workAdd coefficients to make this work Save oxygen and hydrogen until last to balanceSave oxygen and hydrogen until last to balance Zn(s) + HCl(aq)  H 2 (g) + ZnCl 2 (aq) Zn(s) + HCl(aq)  H 2 (g) + ZnCl 2 (aq) 10Chemistry Chapter 8

11. Other symbols used – see page 246 See table 8-2 onSee table 8-2 on 11Chemistry Chapter 8

12. Discuss Translate the following equations into sentences:Translate the following equations into sentences: 2ZnO(s) + C(s)  2Zn(s) + CO 2 (g)2ZnO(s) + C(s)  2Zn(s) + CO 2 (g) Solid zinc oxide and solid carbon react to produce solid zinc metal and carbon dioxide gasSolid zinc oxide and solid carbon react to produce solid zinc metal and carbon dioxide gas CS 2 (l) + 3O 2 (g)  CO 2 (g) + 2SO 2 (g)CS 2 (l) + 3O 2 (g)  CO 2 (g) + 2SO 2 (g) Liquid carbon disulfide reacts with oxygen gas to produce carbon dioxide gas and sulfur dioxide gas.Liquid carbon disulfide reacts with oxygen gas to produce carbon dioxide gas and sulfur dioxide gas. NaCl(aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl(s)NaCl(aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl(s) Aqueous solutions of sodium chloride and silver nitrate react to produce aqueous sodium nitrate and a precipitate of silver chloride.Aqueous solutions of sodium chloride and silver nitrate react to produce aqueous sodium nitrate and a precipitate of silver chloride. 12Chemistry Chapter 8

13. Coefficients in chemical equations Indicate relative amounts of reactants and productsIndicate relative amounts of reactants and products Smallest numbers of atoms, molecules, or ions that satisfy conservation of massSmallest numbers of atoms, molecules, or ions that satisfy conservation of mass Smallest whole number ratio of particles or molesSmallest whole number ratio of particles or moles Can be used to find the relative masses of reactants and productsCan be used to find the relative masses of reactants and products Convert number of moles (coefficient) to gramsConvert number of moles (coefficient) to grams 13Chemistry Chapter 8

14. Example 2H 2 O  2H 2 + O 22H 2 O  2H 2 + O 2 2 mol H 2 O produce 2 mol H 2 and 1 mole O 22 mol H 2 O produce 2 mol H 2 and 1 mole O 2 2*18.02 = 36.04 g H 2 O2*18.02 = 36.04 g H 2 O 2*2.02 = 4.04 g H 22*2.02 = 4.04 g H 2 32.00 g O 232.00 g O 2 36.04 g H 2 O produce 4.04 g H 2 and 32.00 g O 236.04 g H 2 O produce 4.04 g H 2 and 32.00 g O 2 14Chemistry Chapter 8

15. Balancing equations 1.Make sure the formulas in the equation are correct. 2.Balance the elements that appear only once on each side of the equation. 3.Balance polyatomic ions that appear on each side of the equation as single units 4.Balance O atoms and H atoms last 5.Count atoms to make sure the equation is balanced 15Chemistry Chapter 8

16. Common errors The formulas are incorrect to begin with.The formulas are incorrect to begin with. Subscripts get changed in an attempt to balance.Subscripts get changed in an attempt to balance. Coefficients don’t represent the smallest whole number ratio.Coefficients don’t represent the smallest whole number ratio. 16Chemistry Chapter 8

17. Example Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas.Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. Ca(s) + H 2 O(l)  Ca(OH) 2 (aq) + H 2 (g) Ca(s) + H 2 O(l)  Ca(OH) 2 (aq) + H 2 (g) 17Chemistry Chapter 8

18. Example Nitrogen dioxide gas reacts with water to form aqueous nitric acid and nitrogen monoxide gas.Nitrogen dioxide gas reacts with water to form aqueous nitric acid and nitrogen monoxide gas. NO 2 (g) + H 2 O(l)  HNO 3 (aq) + NO(g) NO 2 (g) + H 2 O(l)  HNO 3 (aq) + NO(g) 18Chemistry Chapter 8

19. You try Solid potassium chlorate decomposes to form solid potassium chloride and oxygen gas.Solid potassium chlorate decomposes to form solid potassium chloride and oxygen gas. KClO 3 (s)  KCl(s) + O 2 (g) KClO 3 (s)  KCl(s) + O 2 (g) 19Chemistry Chapter 8

20. You try H 2 SO 4 (aq)+ BaCl 2 (aq)  HCl(aq) + BaSO 4 (s)H 2 SO 4 (aq)+ BaCl 2 (aq)  HCl(aq) + BaSO 4 (s) Al 2 O 3 (s)+ H 2 SO 4 (aq)  Al 2 (SO 4 ) 3 (aq)+ H 2 O(l)Al 2 O 3 (s)+ H 2 SO 4 (aq)  Al 2 (SO 4 ) 3 (aq)+ H 2 O(l) 20Chemistry Chapter 8

21. Discuss Write the word and balanced chemical equations for the reaction that occurs when hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water.Write the word and balanced chemical equations for the reaction that occurs when hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water. Hydrogen peroxide  oxygen + waterHydrogen peroxide  oxygen + water 2H 2 O 2 (aq)  O 2 (g) + 2H 2 O(l)2H 2 O 2 (aq)  O 2 (g) + 2H 2 O(l) 21Chemistry Chapter 8

22. 5 basic types of chemical reactions SynthesisSynthesis DecompositionDecomposition Single replacementSingle replacement Double replacementDouble replacement CombustionCombustion 22Chemistry Chapter 8

23. Synthesis AKA compositionAKA composition Two or more substances combine to form a new compoundTwo or more substances combine to form a new compound A + X  AXA + X  AX More than one reactant and only one productMore than one reactant and only one product 23Chemistry Chapter 8

24. Oxides Created when an element combines with oxygen in a synthesis reactionCreated when an element combines with oxygen in a synthesis reaction 2Mg(s) + O 2 (g)  2MgO(s)2Mg(s) + O 2 (g)  2MgO(s) 24Chemistry Chapter 8

25. Oxides Some metals can form two different oxidesSome metals can form two different oxides 2Fe(s) + O 2 (g)  2FeO(s)2Fe(s) + O 2 (g)  2FeO(s) 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s)4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s) 25Chemistry Chapter 8

26. Metals and halogens Most metals react with halogensMost metals react with halogens 2Na(s) + Cl 2 (g)  2NaCl(s)2Na(s) + Cl 2 (g)  2NaCl(s) 2Co(s) + 3F 2 (g)  2CoF 3 (s)2Co(s) + 3F 2 (g)  2CoF 3 (s) 26Chemistry Chapter 8

27. Synthesis with oxides Oxides of active metals react with water to make metal hydroxides, which are bases.Oxides of active metals react with water to make metal hydroxides, which are bases. CaO(s) + H 2 O(l)  Ca(OH) 2 (s)CaO(s) + H 2 O(l)  Ca(OH) 2 (s) Oxides of nonmetals often react with water to produce acidsOxides of nonmetals often react with water to produce acids SO 3 (g) + H 2 O(l)  H 2 SO 4 (aq)SO 3 (g) + H 2 O(l)  H 2 SO 4 (aq) 27Chemistry Chapter 8

28. Decomposition reactions A single compound produces two or more simpler substancesA single compound produces two or more simpler substances AX  A + XAX  A + X Only 1 reactant and more than 1 productOnly 1 reactant and more than 1 product 28Chemistry Chapter 8

29. Binary compound Decompose into elements that make it upDecompose into elements that make it up 2H 2 O(l) 2H 2 (g) + O 2 (g)2H 2 O(l) 2H 2 (g) + O 2 (g) Electrolysis – decomposition by an electric currentElectrolysis – decomposition by an electric current electricity 29Chemistry Chapter 8

30. Metal Carbonates Decompose to produce a metal oxide and carbon dioxide gasDecompose to produce a metal oxide and carbon dioxide gas CaCO 3 (s)  CaO(s) + CO 2 (g)CaCO 3 (s)  CaO(s) + CO 2 (g) 30Chemistry Chapter 8

31. Metal Hydroxides Most decompose to make metal oxides and waterMost decompose to make metal oxides and water Ca(OH) 2 (s)  CaO(s) + H 2 O(l)Ca(OH) 2 (s)  CaO(s) + H 2 O(l) 31Chemistry Chapter 8

32. Metal Chlorates Decompose to produce a metal chloride and oxygenDecompose to produce a metal chloride and oxygen 2KClO 3 (s)  2KCl(s) + 3O 2 (g)2KClO 3 (s)  2KCl(s) + 3O 2 (g) 32Chemistry Chapter 8

33. Decomposition of Acids Some decompose into nonmetal oxides and waterSome decompose into nonmetal oxides and water Carbonic acid decomposes into carbon dioxide and waterCarbonic acid decomposes into carbon dioxide and water Sulfuric acid decomposes into sulfur trioxide and waterSulfuric acid decomposes into sulfur trioxide and water Sulfurous acid decomposes into sulfur dioxide and waterSulfurous acid decomposes into sulfur dioxide and water 33Chemistry Chapter 8

34. Discuss After hearing about the discovery of oxygen in 1774, Antoine Lavoisier began an experiment to study the nature of burning. He slowly heated mercury in air to produce mercury (II) oxide. He then strongly heated the mercury (II) oxide until he had recovered the mercury and the oxygen.After hearing about the discovery of oxygen in 1774, Antoine Lavoisier began an experiment to study the nature of burning. He slowly heated mercury in air to produce mercury (II) oxide. He then strongly heated the mercury (II) oxide until he had recovered the mercury and the oxygen. Write the equations for both the synthesis reaction and the decomposition reaction described above.Write the equations for both the synthesis reaction and the decomposition reaction described above. 34Chemistry Chapter 8

35. Single-replacement reactions AKA displacementAKA displacement One element replaces a similar element in a compoundOne element replaces a similar element in a compound A + BX  AX + BA + BX  AX + B Y + BX  BY + XY + BX  BY + X 35Chemistry Chapter 8

36. Metals displacing metals A more active metal may replace another metal in a compoundA more active metal may replace another metal in a compound 2Al(s) +3Pb(NO 3 ) 2 (aq)  3Pb(s) +2Al(NO 3 ) 3 (aq)2Al(s) +3Pb(NO 3 ) 2 (aq)  3Pb(s) +2Al(NO 3 ) 3 (aq) 36Chemistry Chapter 8

37. Metals displacing hydrogen in water Active metals react with water to form metal hydroxides and hydrogen gasActive metals react with water to form metal hydroxides and hydrogen gas 2Na(s) + 2H 2 O(l)  2NaOH(aq) + H 2 (g)2Na(s) + 2H 2 O(l)  2NaOH(aq) + H 2 (g) Less active metals react with steam to form metal oxides and hydrogen gasLess active metals react with steam to form metal oxides and hydrogen gas 3Fe(s) + 2H 2 O(g)  Fe 3 O 2 (s) + 2H 2 (g)3Fe(s) + 2H 2 O(g)  Fe 3 O 2 (s) + 2H 2 (g) 37Chemistry Chapter 8

38. Metals displacing hydrogen in acids Produce a salt and hydrogen gasProduce a salt and hydrogen gas Zn(s) + 2HCl(aq)  H 2 (g) + ZnCl 2 (aq)Zn(s) + 2HCl(aq)  H 2 (g) + ZnCl 2 (aq) 38Chemistry Chapter 8

39. Halogens replacing halogens More active ones replace othersMore active ones replace others Can replace any below itCan replace any below it Cl 2 (g) + 2KBr(aq)  2KCl(aq) + Br 2 (l)Cl 2 (g) + 2KBr(aq)  2KCl(aq) + Br 2 (l) 39Chemistry Chapter 8

40. Double replacement reactions AKA double displacementAKA double displacement The ions of two compounds exchange places to form two new compoundsThe ions of two compounds exchange places to form two new compounds The ions switch partnersThe ions switch partners AX + BY  AY + BXAX + BY  AY + BX 40Chemistry Chapter 8

41. Precipitate formation 2KI(aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2KNO 3 (aq)2KI(aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2KNO 3 (aq) 41Chemistry Chapter 8

42. Gas formation FeS(s) + 2HCl(aq)  H 2 S(g) + FeCl 2 (aq)FeS(s) + 2HCl(aq)  H 2 S(g) + FeCl 2 (aq) 42Chemistry Chapter 8

43. Water formation HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l)HCl(aq) + NaOH(aq)  NaCl(aq) + H 2 O(l) 43Chemistry Chapter 8

44. Combustion reactions Burning by combining with oxygenBurning by combining with oxygen Energy released as light and heatEnergy released as light and heat Must have O 2 as a reactantMust have O 2 as a reactant 2H 2 (g) + O 2 (g)  2H 2 O(g)2H 2 (g) + O 2 (g)  2H 2 O(g) 44Chemistry Chapter 8

45. Burning hydrocarbons Hydrocarbons contain only hydrogen and carbonHydrocarbons contain only hydrogen and carbon When they burn, they always produce carbon dioxide and steamWhen they burn, they always produce carbon dioxide and steam C 3 H 8 (g) + 5O 2 (g)  3CO 2 (g) + 4H 2 O(g)C 3 H 8 (g) + 5O 2 (g)  3CO 2 (g) + 4H 2 O(g) CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g)CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) 45Chemistry Chapter 8

46. Activity The ability of an element to reactThe ability of an element to react For metals – how easily they lose electronsFor metals – how easily they lose electrons For nonmetals – how easily they gain electronsFor nonmetals – how easily they gain electrons 46Chemistry Chapter 8

47. Activity series A list of elements arranged according to how easily they undergo certain chemical reactionsA list of elements arranged according to how easily they undergo certain chemical reactions See table 8-3 on page 266See table 8-3 on page 266 Help determine whether or not a reaction will actually take placeHelp determine whether or not a reaction will actually take place 47Chemistry Chapter 8

48. Single displacement reactions An element in a series can displace any element below it, but no element above it.An element in a series can displace any element below it, but no element above it. Often related to position on the periodic tableOften related to position on the periodic table Can displace elements below, but not aboveCan displace elements below, but not above 48Chemistry Chapter 8

49. Example Using table 8-3, predict whether the following reactions will occur. If they will, write the products and balance the equation.Using table 8-3, predict whether the following reactions will occur. If they will, write the products and balance the equation. MgCl 2 (aq) + Zn(s) MgCl 2 (aq) + Zn(s)  No reaction, because Zn cannot displace MgNo reaction, because Zn cannot displace Mg Al(s) + H 2 O(g) Al(s) + H 2 O(g)  Yes, Al can displace H in steamYes, Al can displace H in steam 2Al(s) + 3H 2 O(g)  Al 2 O 3 (s) + 3H 2 (g)2Al(s) + 3H 2 O(g)  Al 2 O 3 (s) + 3H 2 (g) 49Chemistry Chapter 8

50. You try Using table 8-3, predict whether the following reactions will occur. If they will, write the products and balance the equation.Using table 8-3, predict whether the following reactions will occur. If they will, write the products and balance the equation. Cd(s) + O 2 (g) Cd(s) + O 2 (g)  Cd reacts with oxygen forming an oxideCd reacts with oxygen forming an oxide 2Cd(s) + O 2 (g)  2CdO(s)2Cd(s) + O 2 (g)  2CdO(s) I 2 (s) + KF(g) I 2 (s) + KF(g)  No reaction, because I cannot replace FNo reaction, because I cannot replace F 50Chemistry Chapter 8

51. You try Identify the halogen that will not replace any other halogen in a compound.Identify the halogen that will not replace any other halogen in a compound. IodineIodine Identify the halogen that will not be replaced by any of the other halogensIdentify the halogen that will not be replaced by any of the other halogens FluorineFluorine 51Chemistry Chapter 8