33 Concentration&Electrolytic Cells

33 Concentration&Electrolytic Cells - Here are the...

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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. Javits 109 106850584 – 999999999 Light Engineering 102 106769583 – 106804441 Engineering 145 106723217 – 106769582 Javits 102 106589340 – 106625288 Javits 101 106804442 – 106850583 Engineering 143 106694164 – 106723216 Harriman Hall 137 106651275 – 106694163 Javits 110 106625289 – 106651274 Old Chemistry 116 106538503 – 106589339 Javits 100 balcony 106247115 – 106538502 Javits 100 main floor 000000000 – 106247114 Room Solar ID Room Assignments for Exam 3 Tuesday, April 21st, 8:30 – 10:00 PM
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This note was uploaded on 02/13/2011 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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33 Concentration&amp;Electrolytic Cells - Here are the...

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