Chemical Equations

Chemical Equations Chapter 8 : 

1 Chemical Equations Chapter 8 Hein and Arena Eugene Passer Chemistry Department Bronx Community College © John Wiley and Sons, Inc Version 2.0 12th Edition

Chapter Outline : 

2 Chapter Outline 8.1 The Chemical Equation 8.2 Writing and Balancing Chemical Equations 8.3 Information in a Chemical Equation 8.4 Types of Chemical Equations 8.5 Heat in Chemical Reactions

Slide 3: 

3 Chemists use chemical equations to describe reactions they observe in the laboratory or in nature. Chemical equations provide us with the means to summarize the reaction display the substances that are reacting show the products indicate the amounts of all component substances in a reaction.

8.1The Chemical Equation : 

4 8.1The Chemical Equation

Slide 5: 

5 Chemical reactions always involve change. Atoms, molecules or ions rearrange to form different substances. The substances entering the reaction are called reactants. The substances formed in the reaction are called products. During reactions, chemical bonds are broken and new bonds are formed.

Slide 6: 

6 A chemical equation uses the chemical symbols and formulas of the reactants and products and other symbolic terms to represent a chemical reaction. A chemical equation is a shorthand expression for a chemical change or reaction.

Slide 7: 

7 Al + Fe2O3  Fe + Al2O3 Chemical Equation

Slide 8: 

8 Coefficients (whole numbers) are placed in front of substances to balance the equation and to indicate the number of units (atoms, molecules, moles, or ions) of each substance that are reacting.

Slide 9: 

9 Al + Fe2O3  Fe + Al2O3

Slide 10: 

10 Conditions required to carry out the reaction may be placed above or below the arrow.

Slide 11: 

11  heat

Slide 12: 

12 The physical state of a substance is indicated by symbols such as (l) for liquid.

Slide 13: 

13 2Al(s) + Fe2O3(s)  2Fe(l) + Al2O3 (s) All atoms present in the reactant must also be present in the products. In a chemical reaction atoms are neither created nor destroyed.

Symbols Usedin Chemical Reactions : 

14 Symbols Usedin Chemical Reactions

Slide 15: 

15 placed between substances + symbol plus meaning location

Slide 16: 

16  symbol yields meaning between reactants and products location

Slide 17: 

17 (s) symbol after formula location

Slide 18: 

18 (l) symbol location after formula

Slide 19: 

19 (g) symbol location after formula

Slide 20: 

20 (aq) symbol

Slide 21: 

21  symbol

Slide 22: 

22 h symbol

Slide 23: 

23  symbol

8.2Writing andBalancing Equations : 

24 8.2Writing andBalancing Equations

Slide 25: 

25 To balance an equation adjust the number of atoms of each element so that they are the same on each side of the equation. Never change a correct formula to balance an equation.

Steps for Balancing Equations : 

26 Steps for Balancing Equations

Slide 27: 

27 Step 1 Identify the reaction. Write a description or word equation for the reaction. Mercury (II) oxide decomposes to form mercury and oxygen. mercury(II) oxide → mercury + oxygen

Slide 28: 

28 HgO  Hg + O2 The formulas of the reactants and products must be correct. The reactants are written to the left of the arrow and the products to the right of the arrow. Step 2 Write the unbalanced (skeleton) equation. The formulas of the reactants and products can never be changed.

Slide 29: 

29 Step 3a Balance the equation. Count and compare the number of atoms of each element on both sides of the equation. Determine the elements that require balancing.

Slide 30: 

30 HgO → Hg + O2 Step 3a Balance the equation. There is one mercury atom on the reactant side and one mercury atom on the product side. Mercury is balanced. Element Reactant Side Product Side Hg 1 1

Slide 31: 

31 Element Reactant Side Product Side O 1 2 Step 3a Balance the equation. There are two oxygen atoms on the product side and there is one oxygen atom on the reactant side. Oxygen needs to be balanced. HgO  Hg + O2

Slide 32: 

32 Step 3b Balance the equation. Balance each element one at a time, by placing whole numbers (coefficients) in front of the formulas containing the unbalanced element. A coefficient placed before a formula multiplies every atom in the formula by that coefficient.

Slide 33: 

33 Element Reactant Side Product Side O 1 2 Oxygen (O) is balanced. Step 3b Balance the equation. Place a 2 in front of HgO to balance O. There are two oxygen atoms on the reactant side and there are two oxygen atoms on the product side. HgO  Hg + O2

Slide 34: 

34 Step 3c Balance the equation. Check all other elements after each individual element is balanced to see whether, in balancing one element, another element became unbalanced.

Slide 35: 

35 Element Reactant Side Product Side Hg 2 1 Count and compare the number of mercury (Hg) atoms on both sides of the equation. Step 3c Balance the equation. Mercury (Hg) is not balanced. 2HgO  Hg + O2 There are two mercury atoms on the reactant side and there is one mercury atom on the product side.

Slide 36: 

36 2HgO  Hg + O2 Step 3c Balance the equation. Place a 2 in front of Hg to balance mercury. Mercury (Hg) is balanced. There are two mercury atoms on the reactant side and there are two mercury atoms on the product side. Element Reactant Side Product Side Hg 2 1

Slide 37: 

37 2HgO  2Hg + O2 Element Reactant Side Product Side Hg 2 2 O 2 2  THE EQUATION IS BALANCED

Slide 38: 

38 sulfuric acid + sodium hydroxide → sodium sulfate + water Balance the Equation

Slide 39: 

39 There is one Na on the reactant side and there aretwo Na on the product side. Reactant Side Product Side 1 1 Na 1 2 O 1 1 H 3 2 2 H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l) 2 Place a 2 in front of NaOH to balance Na. Balance the Equation 2 4

Slide 40: 

40 H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l) There are 4 H on the reactant side and two H on the product side. Reactant Side Product Side 1 1 Na 2 2 O 2 1 H 4 2 2 Place a 2 in front of H2O to balance H. 2 2 4  THE EQUATION IS BALANCED 

Slide 41: 

41 butane + oxygen → carbon dioxide + water Balance the Equation

Slide 42: 

42 C4H10 (g) + O2 (g) → CO2(g) + H2O(l) There are four C on the reactant side and there isone C on the product side. Reactant Side Product Side C 4 1 H 10 2 O 2 3 4 Place a 4 in front of CO2 to balance C. 9 4 Balance the Equation

Slide 43: 

43 C4H10 (g) + O2 (g) → CO2(g) + H2O(l) There are 10 H on the reactant side and there aretwo H on the product side. Reactant Side Product Side C 4 4 H 10 2 O 2 9 Place a 5 in front of H2O to balance H. 4 5 10 13

Slide 44: 

44 C4H10 (g) + O2 (g) → CO2(g) + H2O(l) There is no whole number coefficient that can be placed in front of O2 to balance O. Reactant Side Product Side C 4 4 H 10 10 O 2 13 To balance O, double the coefficients of each substance other than oxygen. 5 4 5

Slide 45: 

45 There are now 26 O on the product side. Reactant Side Product Side C 8 8 H 20 20 O 2 26 13 Place a 13 in front of O2 to balance O. 26  THE EQUATION IS BALANCED 

8.3Information in a Chemical Equation : 

46 8.3Information in a Chemical Equation

The meaning of a formulais context dependent. : 

47 The meaning of a formulais context dependent. The formula H2O can mean: 2H and 1 O atom 1 molecule of water 1 mol of water 6.022 x 1023 molecules of water 18.02 g of water

In an equation, formulas can represent units of individual chemical entities or moles. : 

48 In an equation, formulas can represent units of individual chemical entities or moles.

Slide 49: 

49 Formulas Number of molecules Number of atoms Number of moles Molar masses

8.4Types of Chemical Equations : 

50 8.4Types of Chemical Equations

Slide 51: 

51 Combination Decomposition Single-Displacement Double-Displacement

Combination Reactions : 

52 Combination Reactions

Slide 53: 

53 A + B  AB Two reactants combine to form one product.

Examples : 

54 Examples

Slide 55: 

55 2Ca(s) + O2(g)  2CaO(s) Metal + Oxygen → Metal Oxide 4Al(s) + 3O2(g)  2Al2O3(s)

Slide 56: 

56 S(s) + O2(g)  SO2(g) Nonmetal + Oxygen → Nonmetal Oxide N2(g) + O2(g)  2NO(g)

Slide 57: 

57 2K(s) + F2(g)  2KF(s) Metal + Nonmetal → Salt 2Al(s) + 3Cl2(g)  2AlCl3(s)

Slide 58: 

58 Na2O(s) + H2O(l)  2NaOH(aq) Metal Oxide + Water → Metal Hydroxide CaO(s) + 2H2O(l)  2Ca(OH)2(aq)

Slide 59: 

59 SO3(g) + H2O(l)  H2SO4(aq) Nonmetal Oxide + H2O(l) → Oxy-acid N2O5(g) + H2O(l)  2HNO3(aq)

Decomposition Reactions : 

60 Decomposition Reactions

Slide 61: 

61 AB  A + B A single substance breaks down togive two or more different substances.

Examples : 

62 Examples

Slide 63: 

63 Metal Oxide → Metal + Oxygen Metal Oxide → Metal Oxide + Oxygen

Slide 64: 

64 Carbonate → CO2(g) Hydrogen Carbonate → CO2(g)

Slide 65: 

65 Miscellaneous Reactions

Single Displacement Reactions : 

66 Single Displacement Reactions

Slide 67: 

67 A + BC  AC + B One element reacts with a compound toreplace one of the elements of that compound.

Slide 68: 

68 Mg(s) + 2HCl(aq)  H2(g) + MgCl2(aq) 2Al(s) + 3H2SO4(aq)  3H2(g) + Al2(SO4)3(aq) salt Metal + Acid → Hydrogen + Salt salt

Slide 69: 

69 2Na(s) + 2H2O(l)  H2(g) + 2NaOH(aq) Ca(s) + 2H2O(l)  H2(g) + Ca(OH)2(aq) Metal + Water → Hydrogen + Metal Hydroxide metal hydroxide metal hydroxide

Slide 70: 

70 Metal + Water → Hydrogen + Metal Oxide metal oxide

The Activity Series : 

71 The Activity Series

Slide 72: 

72 Metals KCaNaMgAlZnFeNiSnPbHCuAgHg An atom of an element in the activity series will displace an atom of an element below it from one of its compounds . increasing activity

Examples Metal Activity Series : 

73 Examples Metal Activity Series

Slide 74: 

74 Mg(s) + PbS(s)  MgS(s) + Pb(s) Metal Higher in Activity Series Displacing Metal Below It Metals MgAlZnFeNiSnPb

Slide 75: 

75 Ag(s) + CuCl2(s)  no reaction Metal Lower in Activity Cannot Displace Metal Above It Metals PbHCuAgHg

ExampleHalogen Activity Series : 

76 ExampleHalogen Activity Series

Slide 77: 

77 Cl2(g) + CaBr2(s)  CaCl2(aq) + Br2(aq) Halogen Higher in Activity Series Displaces Halogen Below It Halogens F2Cl2Br2I2

Double Displacement Reactions : 

78 Double Displacement Reactions

Slide 79: 

79 AB + CD  AD + CB Two compounds exchange partners with each other to produce two different compounds. The reaction can be thought of as an exchange of positive and negative groups.

The Following Accompany Double Displacement Reactions : 

80 The Following Accompany Double Displacement Reactions formation of a precipitate release of gas bubbles release of heat formation of water

Examples : 

81 Examples

Slide 82: 

82 Acid Base Neutralization HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l) acid + base → salt + water

Slide 83: 

83 Formation of an Insoluble Precipitate AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq)

Slide 84: 

84 Metal Oxide + Acid CuO(s) + 2HNO3(aq)  Cu(NO3)2(aq) + H2O(l) CaO(s) + 2HCl(aq)  CaCl2(s) + H2O(l) metal oxide + acid → salt + water

Slide 85: 

85 Formation of a Gas H2SO4(aq) + 2NaCN(aq)  Na2SO4(aq) + 2HCN(g) NH4Cl(aq) + NaOH(aq)  NaCl(aq) + NH4OH(aq) NH4OH(aq)  NH3(g) + H2O(l) indirect gas formation

8.5Heat inChemical Reactions : 

86 8.5Heat inChemical Reactions

Energy changes always accompany chemical reactions. : 

87 Energy changes always accompany chemical reactions. One reason why reactions occur is that the product attains a lower energy state than the reactants. When this occurs, energy is released to the surroundings.

Slide 88: 

88 H2(g) + Cl2(g) → 2HCl(g) + 185 kJ (exothermic) N2(g) + O2(g) + 185 kJ → 2NO(g) (exothermic) Exothermic reactions liberate heat. Endothermic reactions absorb heat.

For life on Earth the sun is the major provider of energy. : 

89 For life on Earth the sun is the major provider of energy. The energy for plant photosynthesis is derived from the sun. glucose 6CO2 + 6H2O + 2519 kJ → C6H12O6 + 6O2

Energy of Activation : 

90 Energy of Activation

Slide 91: 

91 A certain amount of energy is always required for a reaction to occur. The energy required to start a reaction is called the energy of activation.

Slide 92: 

92 This reaction will not occur unless activation energy is supplied. The activation energy can take the form of a spark or a flame. CH4 + 2O2 → CO2 + 2H2O + 890 kJ

Slide 93: 

93

Slide 94: 

94 The End