C401Ch18LN3 - Chapter 18: Electrochemistry Part 3...

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Chapter 18: Electrochemistry Part 3 Electrolytic Cells Voltaic Cells contain spontaneous rxns. These cells will run spontaneously until equilibrium is reached at E = 0. If it is battery, at equilibrium the battery is dead! But what if we want a redox rxn to occur in a electrochemical cell? What do we do? We can force a nonspontaneous redox rxn to occur if we put electrical energy into the cell! So this is basically the reverse of a voltaic cell: instead of obtaining electrical work, we have to put in electrical work. In the galvanic cell, chemical energy is converted to electrical energy, while in the electrolytic cell electrical energy is converted to chemical energy. Redox rxns where we put in electrical work to force them to occur are called electrolysis rxns and we conduct them in electrolytic cells. Here is an example of an electrolytic cell with its sign conventions: 2 NaCl(l) ± 2 Na(l) + Cl 2 (g) Note that the cathode is still a reduction rxn, while the anode is the oxidation. But what about the sign of the cathode and anode? They’ve swapped! Now the cathode is – while the anode is +.
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C401Ch18LN3 - Chapter 18: Electrochemistry Part 3...

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