hp-chap16 (1) - Chapter 16 Electrochemistry Important...

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GT 6e Zumdahl Chapter 16 1 11/13/09 Important Chapter - ties together several concepts from earlier in the course Oxidation-Reduction Electrochemical Cells Acid-Base Solubility Equilibrium constants Practical Importance Energy storage – batteries Energy conversion – solar cells Chemical conversion E.g., printed circuits – metal deposition Corrosion Corrosion prevention Chapter 16 Electrochemistry
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GT 6e Zumdahl Chapter 16 2 11/13/09 Chapter 16 Electrochemistry Review of Common Terms Term Oxidation State Change Electron Change 1 Oxidation increase loss of electrons e.g., Cu to Cu 2+ (0 to +2) 2 Reduction decrease gain of electrons e.g., Ni + to Ni (+1 to 0) 3 Oxidizing Agent decrease picks up electrons e.g., O 2 to oxide (0 to -2) 4 Reducing Agent increase supplies electrons e.g., H 2 to H 2 O (0 to +1) 5 Substance Oxidized increase loses electrons e.g., Mg to MgO (0 to +2) 6 Substance Reduced decrease gains electrons e.g., CuO to Cu (+2 to 0) Review Chapter 4 for oxidation reduction and balancing redox reactions
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GT 6e Zumdahl Chapter 16 3 11/13/09 Copper strip in Cu(NO 3 ) 2 solution Silver strip in Ag(NO 3 ) 2 solution Electrochemical Cells
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GT 6e Zumdahl Chapter 16 4 11/13/09 Electrochemical Cells Cu(s) + 2Ag + (aq) → Cu ++ (aq) + 2Ag(s) Silver plates spontaneously ΔG f < 0 Called a galvanic or voltaic cell OxidationCu → Cu ++ + 2e - Reduction Ag + + e - → Ag
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GT 6e Zumdahl Chapter 16 5 11/13/09 Cu(s) + 2Ag + (aq) → Cu ++ (aq) + 2Ag(s) Oxidation occurs here at the anode Reduction occurs here at the cathode Chemical energy converted to Electrical Energy. This potential difference can be measured. Current = charge/time or I=Q/t Units: amperes = coulombs/sec.
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GT 6e Zumdahl Chapter 16 6 11/13/09 Cu(s) + 2Ag + (aq) → Cu ++ (aq) + 2Ag(s) Convention for this reaction Cu(s) | Cu +2 (aq) ¦¦ Ag+(aq) | Ag(s) Anode or Oxidation is always on the left Cathode or Reduction is always on the right
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GT 6e Zumdahl Chapter 16 7 11/13/09 If an opposing electric force is applied the reverse reaction occurs, called an electrolytic cell Cu ++ (aq) + 2Ag(s)→ Cu(s) +2Ag + (aq) The electrodes are reversed Ag becomes the anode Cu becomes the cathode Note that the electron flow is still anode to cathode Ag + (aq) | Ag(s) ¦¦ Cu(s) | Cu +2 (aq)
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GT 6e Zumdahl Chapter 16 8 11/13/09 Half-Cell Potentials Or Standard Half Cell Reduction Potentials
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GT 6e Zumdahl Chapter 16 9 11/13/09 This section introduces Standard half cell reduction potentials xxxxxxxxxxxxxxxxxxxxxxxxxxxx Tables list half cell reactions as reductions . Note that these are all listed as reductions.
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GT 6e Zumdahl Chapter 16 10 11/13/09 Standard Reduction potentials E ° Ni 2+ + 2e - → Ni (s)-0.257 Volts Cu 2+ + 2e - → Cu (s) +0.345 Volts Note used OFB 4 th edition corrected values Now if we combine these as two separate cells (as we did in chapter 12) Cu 2+ reduction potential is more positive (+0.345) therefore it is Reduced (cathode) and Ni is oxidized (anode) Δ = E° (cathode) - (anode) = 0.345 (– 0.257) = 0.602 volts Notice that we want the opposite of the Nickel reduction potential, therefore the minus sign Ni (s) → Ni 2+ + 2e – (–0.257) Volts Cu 2+ + 2e - → Cu (s) +0.345 Volts Cu 2+ + Ni → Cu (s) + Ni 2+ Net Equation
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hp-chap16 (1) - Chapter 16 Electrochemistry Important...

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