Chapter 5 Chemical Reactions and Quantities

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Chapter 5Chemical Reactions and Quantities

• Types of Reactions
• Oxidation-Reduction Reactions

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Type of Reactions

• Chemical reactions are classified into four
  general types
• Combination
• Decomposition
• Single Replacement
• Double Replacement

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Combination (Synthesis)

• Two or more elements or simple compounds combine
  to form (synthesize) one product
• A B AB
• 2Mg O2 2MgO
• 2Na Cl2 2NaCl
• SO3 H2O H2SO4

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Decomposition

• One substance is broken down (split) into two or
  more simpler substances.
• AB A B
• 2HgO 2Hg O2
• 2KClO3 2KCl 3 O2

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Learning Check R1

• Classify the following reactions as
• 1) combination or 2) decomposition
• ___A. H2 Br2 2HBr
• ___B. Al2(CO3)3 Al2O3 3CO2
• ___C. 4 Al 3C Al4C3

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Solution R1

• Classify the following reactions as
• 1) combination or 2) decomposition
• _1_A. H2 Br2 2HBr
• _2_B. Al2(CO3)3 Al2O3 3CO2
• _1_C. 4 Al 3C Al4C3

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Single Replacement

• One element takes the place of an element in a
  reacting compound.
• A BC AB C
• Zn 2HCl ZnCl2 H2
• Fe CuSO4 FeSO4 Cu

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Double Replacement

• Two elements in reactants take the place of
  each other
• AB CD AD CB
• AgNO3 NaCl AgCl NaNO3
• ZnS 2HCl ZnCl2 H2S

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Learning Check R2

• Classify the following reactions as
• 1) single replacement
• 2) double replacement
• __A. 2Al 3H2SO4 Al2(SO4)3
  3H2
• __B. Na2SO4 2AgNO3 Ag2SO4 2NaNO3
• __C. 3C Fe2O3 2Fe 3CO

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Solution R2

• Classify the following reactions as
• 1) single replacement
• 2) double replacement
• 1_A. 2Al 3H2SO4 Al2(SO4)3
  3H2
• 2_B. Na2SO4 2AgNO3 Ag2SO4 2NaNO3
• 1_C. 3C Fe2O3 2Fe 3CO

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Combustion

• A reaction in which a compound (often carbon)
  reacts with oxygen
• C O2 CO2
• CH4 2O2 CO2 2H2O
• C3H8 5O2 3CO2 4H2O
• C6H12O6 6O2 6CO2 6H2O

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Learning Check R3

• Balance the combustion equation
• ___C5H12 ___O2 ___CO2 ___H2O

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Solution R3

• Balance the combustion equation
• 1 C5H12 8 O2 5 CO2 6
  H2O

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Oxidation and Reduction

• Reactions that involve a loss or gain of
  electrons
• Occurs in many of the 4 types of reactions and
  combustion
• Important in food metabolism, batteries, rusting
  of metals

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Requirements for Oxidization-Reduction

• Electrons are transferred
• Two processes occur
• Oxidation Loss of electrons (LEO)
• Zn Zn2 2e-
• Reduction Gain of electrons (GER)
• Cu2 2e- Cu

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Balanced Red-Ox Equations

• Combine the oxidation and reduction reactions to
  make
• Loss of electrons Gain of electrons
• Zn Cu2 2e- Zn2 2e- Cu
• Zn Cu2 Zn2 Cu

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Gain/Loss of Hydrogen

• In organic and biological reactions
• oxidation Loss of H
• reduction Gain of H

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Learning Check R3

• Identify the following as an 1) oxidation or a
  reduction process
• __A. Sn Sn4 4e-
• __B. Fe3 1e- Fe2
• __C. Cl2 2e- 2Cl-

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Solution R3

• Identify the following as an 1) oxidation or a
  reduction process
• 1_ A. Sn Sn4 4e-
• 2_ B. Fe3 1e- Fe2
• 2_ C. Cl2 2e- 2Cl-

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Learning Check R4

• In light-sensitive sunglasses, UV light
  initiates an oxidation-reduction reaction
• Ag Cl- Ag Cl
• A. Which reactant is oxidized
• 1) Ag 2) Cl- 3) Ag
• B. Which reactant is reduced?
• 1) Ag 2) Cl- 3) Cl

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Solution R4

• In light-sensitive sunglasses, UV light
  initiates an oxidation-reduction reaction
• Ag Cl- Ag Cl
• A. Which reactant is oxidized
• 2) Cl- Cl- Cl e-
• B. Which reactant is reduced?
• 1) Ag Ag e- Ag