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Understanding Oxidation-Reduction Reactions and Electrochemical Cells

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This section delves into oxidation-reduction (redox) reactions, highlighting the concepts of oxidation, reduction, oxidizing agents, and reducing agents. It demonstrates the balancing of half-reactions and how to analyze electrochemical cells where oxidation occurs at the anode and reduction at the cathode. It explains cell potentials, how to calculate them using reduction potentials, and the thermodynamic implications of positive cell potentials. Additionally, the section discusses electrolysis and its applications, including calculating costs for producing materials like aluminum and copper.

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Understanding Oxidation-Reduction Reactions and Electrochemical Cells

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  1. ElectrochemistyElectron Transfer Reaction Section 20.1

  2. Oxidation-Reduction Reactions Oxidation: loss of electrons, increase in oxidation state Reduction: gain of electrons, decrease in oxidation state Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s) Oxidizing Agent: species reduced Reducing Agent: species oxidized

  3. Oxidation-Reduction Reactions Half-reactions and Balancing Redox Equations Zn(s) + Ag+(aq)  Zn2+(aq) + Ag(s) oxidation half-reaction: reduction half-reaction: overall equation: balance half-reactions to eliminate all electrons:

  4. Electrochemical Cells: Performing redox reactions with separated reactants Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)

  5. Electrochemical Cells: Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s) oxidation occurs at “anode” reduction occurs at “cathode”

  6. Section 20.2: Cell Potentials

  7. Determining Cell Potentials Reduction Potentials (a measure of ease of reduction)

  8. Cell Potentials: Strength of oxidizing and reducing agents

  9. Cell Potentials: using reduction potentials to determine cell potentials Eocell = Eored(cathode) – Eored(anode) Determine the cell potential for a cell using the reaction: Cu2+(aq) + Fe(s)  Fe2+(aq) + Cu(s) oxidation occurs at anode reduction occurs at cathode

  10. Cell Potentials: using reduction potentials to determine cell potentials Eocell = Eored(cathode) – Eored(anode) Determine the cell potential for a cell using the reaction: 3 Ag+(aq) + Cr(s)  Cr3+(aq) + 3 Ag(s) oxidation occurs at anode reduction occurs at cathode

  11. Positive Eocellmeans the reaction is thermodynamically product-favored Eocell = Eored(cathode) – Eored(anode) Which reaction is favored: Cu2+(aq) + Fe(s)  Fe2+(aq) + Cu(s) or Fe2+(aq) + Cu(s)  Cu2+(aq) + Fe(s) oxidation occurs at anode reduction occurs at cathode

  12. Positive Eocellmeans the reaction is thermodynamically product-favored For a favored reaction: Choose an oxidizing agent that is ___________________________ from the reducing agent.

  13. Cell Potential (Eocell ) and Free Energy Change (Go) Go = -nFEoF= Faraday’s Constant = 96485 J/Vmol e- Positive Eocellmeans: Go = Kc = System is ____________ - Favored

  14. Go = -nFEoF= Faraday’s Constant = 96485 J/Vmol e- Calculate Go for: 2 Cu2+(aq) + Ni(s)  2 Cu+(aq) + Ni2+(aq) Eored(Ni2+/Ni) = -0.250 V Eored(Cu2+/Cu+) = 0.153 V

  15. Electrolysis: Using electrical energy to drive reactions Electrical Relationships (Part 1): 1 C = 1 amp x 1 second 96485 C = 1 mole- Copper is electroplated onto a metal spoon from a solution of Cu(NO3)2. If a current of 0.460 Amps is run for 15 minutes, what mass of Cu(s) is deposited?

  16. Electrical Relationships (Part 2): 1 C = 1 amp x 1 second 1 Watt = 1 V x 1 A 96485 C = 1 mole- electricity ~ 8 cents/kWh 1 C x 1 V = 1 Wsec Aluminum is produced by reduction of Al3+ ions at a voltage of 4.5 V. What is the cost of producing a 1-pound roll of aluminum foil?

  17. 1 C = 1 amp x 1 second 1 Watt = 1 V x 1 A 96485 C = 1 mole- electricity ~ 8 cents/kWh 1 C x 1 V = 1 Wsec Aluminum is produced by reduction of Al3+ ions at a voltage of 4.5 V. What is the cost of producing a 1-pound roll of aluminum foil?

  18. Batteries: Quantitative Analysis This battery provides 2200 mAh of electricity. How many moles of electrons is this?

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