32 Electrolytic Cells

32 Electrolytic Cells - Here are the standard reduction...

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1 Here are the standard reduction potentials for 2 half- reactions that occur in a rechargeable Ni/Cd battery. What is the standard cell potential? -0.81 volts Cd(s) + 2OH - (aq) + 2e - Cd(OH) 2 (s) +0.44 volts Ni(OH) 3 (s) + e - Ni(OH) 2 (s) + OH - (aq) G o = - n F E o For a spontaneous reaction, you need G o < 0 and E o cell > 0. A) – 1.25 V B) + 1.25 V C) – 0. 37 V D) + 0.37 V 2 The half-reaction with the more positive reduction potential produces the greater decrease in free energy, so it runs as written, i.e. as a reduction reaction. -0.81 volts Cd(OH) 2 (s) + 2e - Cd(s) + 2OH-(aq) +0.44 volts Ni(OH) 3 (s) + 1 e - Ni(OH) 2 (s) + OH - (aq) E o red G o = - n F E o The other half-reaction then must reverse and run as an oxidation reaction. If a reaction reverses, both G o and E o change sign. E o cell = E o reduction + E o oxidation =+1.25 V E o oxidation = - E o reduction
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Rechargeable Batteries A battery is rechargeable if the reactants and products remain at the electrodes. A Ni/Cd battery is rechargeable because the reactants and products all are solids. A Zn/Cu battery is not rechargeable because the Zn 2+ and Cu 2+ ions are in an aqueous solution and diffuse away from the electrodes. In alkaline batteries, the ions are in a paste so the diffusion is limited. They can be recharged but not very effectively, and it must be done slowly so the ions can diffuse back to the electrodes. UG TA POSITIONS AVAILABLE FOR Fall 2010
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This note was uploaded on 04/17/2010 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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32 Electrolytic Cells - Here are the standard reduction...

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