Oxidation Reduction Reactions

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Oxidation Reduction Reactions

• Redox Reactions
• Electron-Transfer Reactions

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Oxidation Numbers A set of rules for tracking
charges for atoms in covalent compounds

• Each atom in a pure element has an oxidation
  number of zero.
• 2. For monatomic ions, the oxidation number is
  equal to the charge on the ion.
• 3. Fluorine always has an oxidation number of 1
  in compounds with all other
• elements.
• 4. Cl, Br, and I always have oxidation numbers of
  1 in compounds, except when
• combined with oxygen or fluorine.
• 5. The oxidation number of H is 1 and of O is 2
  in most compounds.
• Exception for H In compounds with metals, H is
  1.
• Exception for O In peroxides, O22- ion gives O
  an oxidation number of 1.
• 6. The algebraic sum of the oxidation numbers for
  the atoms in a neutral compound
• must be zero in a polyatomic ion, the sum must
  be equal to the ion charge.

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Oxidation States, Energy, the Economy, and
Global Warming
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Oxidation-Reduction Reactions Oxidation loss
of electrons increase in ox Reduction gain
of electrons decrease in ox 4 Fe 3 O2 ?
2 Fe2O3 Oxidizing agent oxidant gains
electrons Reducing agent reductant loses
electrons
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Recognizing Redox Reactions Always involves
changes in oxidation numbers Metals reacting
with Nonmetals 2 Al 3 Br2 ? Al2Br6 Almost
anything with Oxygen 2 Mg O2 ? 2 MgO
S O2 ? SO2 Organic Compounds CH4 2 O2
? CO2 H2O Others, more difficult to detect 5
Fe2 MnO4- 8 H ? 5 Fe3 Mn2 4 H2O
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• 4 Al(s) 3 O2(g) ? 2 Al2O3(s)
• 2. CuO(s) H2(g) ? Cu(s) H2O(?)

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• CaCO3(s) ? CaO(s) CO2(g)
• 4. MnO4-(aq) 5 Fe2(aq) 8 H(aq) ?
  Mn2(aq) 4 H2O(?) 5 Fe3(aq)

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• 2 H2O2(aq) ? 2 H2O(?) O2(g)
• 6. CaCO3(s) 2 H(aq) ? CO2(g) H2O(?)
  Ca2(aq)

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Balancing Redox Reactions
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Combination and Decomposition Reactions
Thermal decomposition of metal carbonates MCO3(s
) ? MO(s) CO2(g)
Combination of two elements to form a
compound Zn S ? ZnS
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Organic Reactions
A. Combustion Reactions Reaction with oxygen gas
to form CO2 and H2O. C3H8(g) 5 O2(g) ? 3
CO2(g) 4 H2O(l)
B. Substitution Reactions Exchange of one atom or
molecular fragment.
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C. Addition Reactions Addition of two molecules
together.
D. Elimination Reactions Ejection of a small
molecule from a larger one.
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E. Isomerization (Rearrangement) Reactions Change
of shape of a molecule without gain or loss of
any atoms.