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Redox Reactions

Redox Reactions

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Redox Reactions

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  1. Redox Reactions EQ: How does the transfer of electrons drive redox reactions?

  2. Review • If an atom loses one electron, what will it’s charge/oxidation number be? • What if it loses 3? • What if it gains 2 electrons?

  3. Redox Reactions • Reduction-Oxidation Reactions • Oxidation #’s change from reactants to products • e- are being transferred

  4. Oxidation vs. Reduction • Oxidation CANNOT occur without reduction • Oxidation—loses electrons, increases oxidation # • Ex: Na → Na+ + e- • LEO • Loss of Electrons

  5. Oxidation vs. Reduction cont. • Reduction—gains electrons, reduces oxidation # • Ex: O2 + 4e- → 2O2- • Hint: “LEO the lion says GER” • Lose Electrons, Oxidation • Gain Electrons, Reduction

  6. Assigning Oxidation #’s • Pure elements = 0 • Ex: H2is 0, as is Al • Hydrogen is always +1 • Oxygen is always -2, except in H2O2 • Group 1 is always +1, Group 2 always +2 • Group 17 is always -1 • Overall sum of ox. #’s: • In a compound = 0 • In a polyatomic ion = ion charge

  7. Practice: • NO • P4O8 • (SO4)-2

  8. Classifying Species • Oxidized species—substance being oxidized, losing electrons • Reduced species—substance being reduced, gaining electrons • Spectator ion—substance does NOT change • Oxidizing agent—substance doing the oxidizing, accepting the electrons • Reducing agent—substance doing the reducing, giving up the electrons

  9. Redox Identification • Assign oxidation #’s • Identify the oxidized & reduced species • Identify the oxidizing & reducing agents • Write balanced half reactions

  10. Practice: • 2 Al + 3 Br2 2AlBr3 • Oxidized species: • Reduced species: • Oxidizing agent: • Reducing agent: • 2 Mg + O2 2 MgO • Oxidized species: • Reduced species: • Oxidizing agent: • Reducing agent:

  11. Writing Half-Reactions • 2 half-reactions per redox • One represents oxidation • One represents reduction • Explicitly show exchange of e- • Must be balanced!!

  12. example • Example: Al + Br2 AlBr3 • Balance the reaction, then determine which is oxidized, which is reduced?

  13. Oxidation Half-Reactions • e- added to product side • Example: 2 Al + 3 Br2 2AlBr3 -Aluminum is being oxidized: 2 Al  2 Al3+ + 6e-

  14. Reduction Half-Reactions • e- added to reactant side • Example: 2 Al + 3 Br2 2AlBr3 -Bromine is being reduced: 6 Br + 6e- 6 Br-

  15. Putting it All Together 2 Al + 3 Br2 2 AlBr3 2 Al  2 Al3+ + 6e- 6 Br + 6e- 6 Br-

  16. More Practice: • Write half reactions for the following. Be sure to identify them as oxidation and reduction. • S + O2 SO2 • N2 + 3Ba  Ba3N2