1. 5. 1 Introduction to Chemical Reactions A
5.1 Introduction to Chemical Reactions A. General Features of Physical and Chemical Changes
A chemical change (a chemical reaction) converts
one substance into another.
Chemical reactions involve:
Breaking bonds in the reactants (starting materials)
Forming new bonds in the products

2. 5. 1 Introduction to Chemical Reactions A
5.1 Introduction to Chemical Reactions A. General Features of Physical and Chemical Changes

3. 5.1 Introduction to Chemical Reactions B. Writing Chemical Equations
A chemical equation uses chemical formulas and other symbols showing what reactants are the starting materials in a reaction and what products are formed.

4. 5.1 Introduction to Chemical Reactions B. Writing Chemical Equations
The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction.

5. 5.1 Introduction to Chemical Reactions B. Writing Chemical Equations

6. 5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Write a balanced chemical equation for
the reaction of propane (C3H8) with
oxygen (O2) to form carbon dioxide (CO2)
and water (H2O).
Example
Step [1]
Write the equation with the correct formulas.

7. 5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Balance the equation with coefficients one
element at a time.
Step [2]
Balance the C’s first:
Balance the H’s next:

8. 5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Balance the equation with coefficients one
element at a time.
Step [2]
Finally, balance the O’s:

9. Balance the Equations __H2 (g) + __O2  __H20 __NO + __O2  __NO2
__CH4 + __Cl2  __CH2Cl2 + __HCl

10. Polyatomic Ions
__Ca3(PO4)2 + __H2SO4  __CaSO4 + __H3PO4

11. Balance the Equation __Al + __H2SO4  __Al2(SO4)3 + __H2
__Na2SO3 + __H3PO4  __H2SO3 + __Na3PO4
__Al + __H2SO4  __Al2(SO4)3 + __H2
__NaSO3 + __H3PO4  __H2SO3 + __Na3PO4

12. Balance the Equation __Mg + __HBr  __MgBr2 + __H2
__KClO3  __KCl + __O2
__CH4 + __Cl2  __CCl4 + __HCl
__Mg + __HBr  __MgBr2 + __H2
__KClO3  __KCl + __O2
__CH4 + __Cl2 __CCl4 + __HCl

13. Balance the Equation __Al2O3 + __HCl  __AlCl3 + __H2O
__Al(OH)3 + __H2SO4  __Al2(SO4)3 + __H2O

14. __Ni + __HCl  __NiCl2 + __H2
__PbS + __O2  __PbO + __SO2
__H3PO4 + __Ca(OH)2  __Ca3(PO4)2 + __H2O

15. __H2SO4 + __NaOH  __Na2SO4 + __H2O
__CO + __O2  __CO2
__S + __O2 + __H2O  __H2SO4

16. 5.3 Types of Reactions
The majority of chemical reactions fall into 6 categories:
combination
decomposition
single replacement
double replacement
oxidation and reduction (Section 5.4)
acid-base (Chapter 9)

17. 5.3 Types of Reactions A. Combination and Decomposition
A combination reaction is the joining of two or more reactants to form a single product.

18. 5.3 Types of Reactions A. Combination and Decomposition
A decomposition reaction is the conversion of a single reactant to two or more products.

19. 5.3 Types of Reactions B. Replacement Reactions
A single replacement reaction is a reaction in which one element replaces another element in a compound to form a different compound and element as products.

20. 5.3 Types of Reactions B. Replacement Reactions

21. 5.3 Types of Reactions B. Replacement Reactions
A double replacement reaction is a reaction in which two compounds exchange “parts”–atoms or ions—to form two new compounds.

22. 5.3 Types of Reactions B. Replacement Reactions

23. Combination, Decomposition, Single Displacement or Double Displacement?
Ni(NO3)2 + Mg  Ni + Mg(NO3)2
2 KI + Sn(NO3)2  SnI2 + 2 KNO3
2 HgO  2 Hg + O2

26. Predicting Reactions

27. Predicting Reactions Combination: N2 + ____  Mg3N2
Decomposition: 2 SO3  2SO2 + ______
Single Replacement: 2 Ag + CuBr2  ______ + ______
Double Replacement: KOH + HI  ______ + _______

28. 5.4 Oxidation and Reduction A. General Features
Oxidation is the loss of electrons from an atom.
Reduction is the gain of electrons by an atom.
Both processes occur together in a single reaction called an oxidation−reduction or redox reaction.
A redox reaction involves the transfer of electrons from one element to another.
A redox reaction always has two components, one that is oxidized and one that is reduced.

29. 5.4 Oxidation and Reduction A. General Features

30. 5.4 Oxidation and Reduction A. General Features
Zn Cu2+
Zn Cu
Each of these processes can be written as an
individual half reaction:
Oxidation half reaction:
Reduction half reaction:

31. 5.4 Oxidation and Reduction A. General Features
Zn Cu2+
Zn Cu
oxidized
reduced
A compound that is reduced while causing another
compound to be oxidized is called an oxidizing agent.
Cu2+ acts as an oxidizing agent because it causes
Zn to lose electrons and become oxidized.

32. 5.4 Oxidation and Reduction A. General Features
Zn Cu2+
Zn Cu
oxidized
reduced
A compound that is oxidized while causing another
compound to be reduced is called a reducing agent.
Zn acts as a reducing agent because it causes
Cu2+ to gain electrons and become reduced.

33. 5.4 Oxidation and Reduction A. General Features

34. 5. 4 Oxidation and Reduction B
5.4 Oxidation and Reduction B. Examples of Oxidation–Reduction Reactions
Iron Rusting
O gains e– and is reduced.
4 Fe(s) O2(g)
2 Fe2O3(s)
neutral Fe
neutral O
Fe3+
O2–
Fe loses e– and is oxidized.

35. 5. 4 Oxidation and Reduction B
5.4 Oxidation and Reduction B. Examples of Oxidation–Reduction Reactions
Zn MnO2
ZnO Mn2O3

36. Zn + 2H+  Zn2+ + H2
Fe3+ + Al  Al3+ + Fe

37. I- + Br2  I2 + Br-
AgBr  Ag + Br2

38. 5. 4 Oxidation and Reduction B
5.4 Oxidation and Reduction B. Examples of Oxidation–Reduction Reactions
Oxidation results in the:
Reduction results in the:
Gain of oxygen atoms
Loss of hydrogen atoms
Loss of oxygen atoms
Gain of hydrogen atoms

39. 5.5 The Mole and Avogadro’s Number
A mole is a quantity that contains 6.02 x 1023 items.
1 mole of C atoms = 6.02 x 1023 C atoms
1 mole of H2O molecules = 6.02 x 1023 H2O molecules
1 mole of Vitamin C molecules = 6.02 x 1023 Vitamin C molecules
The number 6.02 x 1023 is Avogadro’s number.
1.3×1023 kg
Titan, largest moon of Saturn
1.5×1023 kg
Ganymede, largest moon of Jupiter
3.3×1023 kg
Mercury
6.4×1023 kg
Mars

40. How many items do 1 mol of the following contain:
Baseballs
Bicycles
Cheerios
CH4 molecules

41. 5.5 The Mole and Avogadro’s Number
It can be used as a conversion factor to relate the
number of moles of a substance to the number of
atoms or molecules:
1 mol
6.02 x 1023 atoms or
6.02 x 1023 atoms
1 mol
1 mol
6.02 x 1023 molecules or
6.02 x 1023 molecules
1 mol

42. 5.5 The Mole and Avogadro’s Number
Sample Problem 5.5
How many molecules are contained in 5.0 moles
of carbon dioxide (CO2)?
Identify the original quantity and the
desired quantity.
Step [1]

43. 5.5 The Mole and Avogadro’s Number
Step [2]
Write out the conversion factors.
Step [3]
Set up and solve the problem.

44. How many C atoms are there in the following:
2.0 mol
6.0 mol
0.5 mol
25.0 mol

45. How many molecules are contained in each of the following number of moles
2.5mol of penicillin
0.25 mol of NH3
0.4 mol of Sugar
55.3 mol of Acetaminophen

46. 5.6 Mass to Mole Conversions
The formula weight is the sum of the atomic weights of all the atoms in a compound, reported in atomic mass units (amu).
HOW TO Calculate the Formula Weight of a Compound
Example
Calculate the formula weight for FeSO4.
Step [1]
Write the correct formula and determine
the number of atoms of each element from
the subscripts.

47. 5.6 Mass to Mole Conversions
HOW TO Calculate the Formula Weight of a Compound
Multiply the number of atoms of each
element by the atomic weight and add
the results.
Step [2]

48. 5.6 Mass to Mole Conversions A. Molar Mass
The molar mass is the mass of one mole of any substance, reported in grams per mole (g/mol).
The value of the molar mass of a compound in grams equals the value of its formula weight in amu.

49. 5.6 Mass to Mole Conversions B. Relating Grams to Moles
The molar mass relates the number of moles to the number of grams of a substance.
In this way, molar mass can be used as a conversion factor.
The molar mass of H2O is 18.0 g/mol, the conversion factor can be written:

50. 5.6 Mass to Mole Conversions B. Relating Grams to Moles
Sample Problem 5.9
How many moles are present in 100. g of aspirin
(C9H8O4)?
Step [1]
Calculate the molar mass.

51. 5.6 Mass to Mole Conversions B. Relating Grams to Moles
Step [2]
Write out the conversion factors.
The conversion factor is the molar mass, and it can be written in two ways.
Choose the one that places the unwanted unit, grams, in the denominator so that the units cancel:

52. 5.6 Mass to Mole Conversions B. Relating Grams to Moles
Step [3]
Set up and solve the problem.

53. How many moles are contained in the following:
100 g NaCl

54. How many moles are contained in the following:
0.25g Aspirin(C9H8O4)

55. How many moles are contained in the following:
25.5g CH4

56. How many moles are contained in the following:
25g of H2O

57. 5. 6 Mass to Mole Conversions C
5.6 Mass to Mole Conversions C. Relating Grams to Number of Atoms or Molecules
We can also use the molar mass to show the relationship between grams and number of
molecules (or atoms).

58. 5. 6 Mass to Mole Conversions C
5.6 Mass to Mole Conversions C. Relating Grams to Number of Atoms or Molecules
Sample Problem 5.10
How many molecules are in a 325-mg tablet of
aspirin (C9H8O4)?
Step [1]
Find the molar mass

59. 5. 6 Mass to Mole Conversions C
5.6 Mass to Mole Conversions C. Relating Grams to Number of Atoms or Molecules
Step [2]
Write out the conversion factors.

60. 5. 6 Mass to Mole Conversions C
5.6 Mass to Mole Conversions C. Relating Grams to Number of Atoms or Molecules
Step [3]
Set up and solve the problem.

61. How many molecules are present in a 500mg tablet of penicillin (C16H18N2O4S)

62. How many molecules are present in a 500mg tablet of penicillin (C16H18N2O4S)

63. How many molecules are present in a 750mg of Mescaline (Hallucinogenic from peyote) (C11H17NO3)

64. 5.7 Mole Calculations in Chemical Equations
A balanced chemical equation also tell us:
The number of moles of each reactant that combine
The number of moles of each product formed
1 N2(g) +
1 O2(g)
2 NO(g)
(The coefficient “1” has been written for emphasis.)

65. 5.7 Mole Calculations in Chemical Equations
Coefficients are used to form mole ratios, which can
serve as conversion factors.
N2(g) +
O2(g)
2 NO(g)
Mole ratios:

66. 5.7 Mole Calculations in Chemical Equations
Sample Problem 5.11
Using the balanced chemical equation, how
many moles of CO are produced from 3.5 moles
of C2H6?
2 C2H6(g) O2(g)
4 CO(g) H2O(g)
Step [1]
Identify the original and desired quantities.

67. 5.7 Mole Calculations in Chemical Equations
2 C2H6(g) O2(g)
4 CO(g) H2O(g)
Step [2]
Write out the conversion factors.
Step [3]
Set up and solve the problem.

68. Complete the following conversions+
O2(g)
2 NO(g)
How many mol of NO are formed from 3.3 mol of N2
How many mol of NO are formed from 0.5mol of O2
How many moles of O2 are needed to completely react with 1.2 mol of N2

69. N2(g) +
O2(g)
2 NO(g)
How many mol of NO are formed from 3.3 mol of N2
How many mol of NO are formed from 0.5mol of O2

70. N2(g) +
O2(g)
2 NO(g)
How many moles of O2 are needed to completely react with 1.2 mol of N2

71. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Using the balanced equation, how many
grams of O3 are formed from 9.0 mol of O2.
Example
sunlight
3 O2(g)
2 O3(g)

72. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Convert the number of moles of reactant
to the number of moles of product using
a mole–mole conversion factor.
Step [1]
sunlight
3 O2(g)
2 O3(g)

73. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Convert the number of moles of product
to the number of grams of product using
the product’s molar mass.
Step [2]

74. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Set up and solve the conversion.
sunlight
3 O2(g)
2 O3(g)

75. C6H12O6 2 C2H6O + 2CO2 (glucose) (ethanol)
How many g of ethanol are formed from 0.55 mol of glucose
How many g of CO2 are formed from 0.25 mol of glucose
How many g of glucose are needed to form 1mol of ethanol

76. How many g of ethanol are formed from 0.55 mol of glucose
C6H12O C2H6O + 2CO2

77. How many g of CO2 are formed from 0.25 mol of glucose
C6H12O C2H6O + 2CO2

78. How many mol of ethanol would be formed if 5g of glucose is used
C6H12O C2H6O + 2CO2

79. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
Ethanol (C2H6O) is synthesized by reacting
ethylene (C2H4) with water.
How many grams of ethanol are formed
from 14 g of ethylene?
Example
C2H H2O
C2H6O

80. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H H2O
C2H6O

81. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H H2O
C2H6O

82. 5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H H2O
C2H6O

84. 2 C2H6(g) O2(g)
4 CO(g) H2O(g)
1) How many molecules of CO is produced?
2) How many g of C2H6 are needed to react with all of O2
3) How many g of H2O are produced when 15g of O2 is used.

85. 4 CO(g) + 6 H2O(g) 2 C2H6(g) + 5 O2(g)
How many molecules of CO is produced?

86. 4 CO(g) + 6 H2O(g) 2 C2H6(g) + 5 O2(g)
How many g of C2H6 are needed to react with all of O2

87. 4 CO(g) + 6 H2O(g) 2 C2H6(g) + 5 O2(g)
How many g of H2O are produced when 15g of O2 is used.

88. 5.9 Percent Yield
The theoretical yield is the amount of product expected from a given amount of reactant based on the coefficients in the balanced chemical equation.
Usually, however, the amount of product formed is less than the maximum amount of product predicted.
The percent yield is the amount of product isolated from a reaction.

89. 5.9 Percent Yield Sample Problem 5.14
If the reaction of ethylene with water to form
ethanol has a calculated theoretical yield of 23 g
of ethanol, what is the percent yield if only 15 g
of ethanol are actually formed?

90. 5.10 Limiting Reactants
The limiting reactant is the reactant that is completely used up in a reaction.

91. 5.10 Limiting Reactant A. Determining the Limiting Reactant
Analyze the two possible outcomes:
If the amount present of the second reactant is less than what is needed, the second reactant is the limiting reagent.
If the amount present of the second reactant is greater than what is needed, the second reactant is in excess.

92. 5.10 Limiting Reactant C. Determining the Limiting Reactant Using the Number of Grams
Sample Problem 5.20
Using the balanced equation, determine the limiting reactant when 10.0 g of N2 (MM = g/mol) react with 10.0 g of O2 (MM = g/mol).
N2(g) O2(g) NO(g)

93. 5.10 Limiting Reactant C. Determining the Limiting Reactant Using the Number of Grams
Sample Problem 5.20
[1] Convert the number of grams of each reactant into moles using the molar masses.

94. 5.10 Limiting Reactant C. Determining the Limiting Reactant Using the Number of Grams
Sample Problem 5.20
[2] Determine the limiting reactant by choosing N as the original quantity and converting to mol O2.
mole–mole
Conversion factor
1 mol O2
1 mol N2
0.357 mol N2 x
= mol O2
The amount of O2 we started with (0.313 mol) is less than the amount we would need (0.357 mol) so O2 is the limiting reagent.

95. N2(g) + O2(g)  NO(g)
Determine the limiting reactant under the following conditions:
1) 12.5g N2 and 15.0g O2
2) 14.0g N2 and 13.0g O2

96. N2(g) + O2(g)  NO(g)
12.5g N2 and 15.0g O2

97. N2(g) + O2(g)  NO(g)
14.0g N2 and 13.0g O2

98. Balance/Rxn Type/ REDOX
Ni + HCl  NiCl2 + H2
CH4 + Cl2  CCl4 + HCl
KClO3  KCl + O2
Al2O3 + HCl  AlCl3 + H2O

102. Given the following reaction:
C12H22O11 + H2O  C2H6O + CO2
(sucrose) (ethanol)
Balance the equation
Determine the molecular weight of sucrose
How many mols of Ethanol would be produced from 2 mols of sucrose?
How many g of ethanol would be produced from 17.1 g sucrose?