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Electrochemistry. Chapter 19. Redox Revisited. Redox Revisited. Redox Revisited. Redox Revisited. Redox Revisited. Redox Revisited. Redox Revisited. Reactivity Revisited. Reactivity Revisited. Reactivity Revisited. TIME. Reactivity Revisited. Voltaic Cells. What is a voltaic cell?.
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Electrochemistry Chapter 19
Reactivity Revisited TIME
Voltaic Cells • What is a voltaic cell? • Device that uses redox reactions to convert chemical energy into electrical energy • Exothermic • Spontaneous • i.e. happens without additional energy • Also called a galvanic or electrochemical cell
Voltaic Cells • What is an electrode? • A metal conductor through which electrons flow • Two types: • Anode – negative • Electrons produced • Oxidation occurring • Cathode– positive • Electrons collected • Reduction occurring
Voltaic Cells • What equilibrium is established between a metal (M) electrode and a solution of its ions? • Equilibrium expression: • Ex. Zinc and Copper • More reactive metal: • Shift right • Creates electrons • Less reactive metal: • Shift left • Accepts electrons More Less
Voltaic Cells • What are the half reactions in a zinc and copper voltaic cell? • Zinc • Oxidized • Zn (s) Zn2+ (aq) + 2e- • Zn2+ goes into solution • Copper • Reduced • Cu2+ (aq) + 2e- Cu (s) • Cu comes out of solution
Voltaic Cells • What is the net reaction? • Combine and cancel: • Zn (s) Zn2+ (aq) + 2e- • Cu2+ (aq) + 2e- Cu (s)________ • Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) • Correct half cell format: • Anode II Cathode • Zn(s) IZn2+(aq) II Cu2+(aq)I Cu(s) Anode Cathode
Voltaic Cells • When will the reaction stop creating electricity? • When one of two of the following occur: • The anode metal completely dissolves • i.e. nothing to oxidize • There are no more cations remaining in the cathode solution • i.e. nothing to reduce
Voltaic Cells • How do you create a complete electrical circuit? • Electrical wire • Connects the electrodes • Salt bridge • Connects the solutions • Electrons will flow from high to low density • Anode (-) to cathode (+) e- flow
Voltaic Cells • What is the purpose of the salt bridge? • A moist substance that was previously soaked in a salt (electrolyte) solution, which allows the movement of ions between the solutions • Helps maintain electrical neutrality - +
Electrolytic Cells • What is an electrolytic cell? • A cell in which electrolysis takes place between two electrodes • Takes place within one solution called an electrolyte • Endothermic • Non-spontaneous • Requires an external electrical source (battery) Battery
Electrolytic Cells • How is an electrical current produced? • The ions in the electrolyte solution move towards the electrode with the opposite charge
Electrolytic Cells • What are the roles of the anode and cathode? • Anode • Oxidation occurs • Positive • Attracts the anions in the electrolyte • Cathode • Reduction occurs • Negative • Attracts the cations in the electrolyte
Electrolytic Cells • Explain the electrolysis of molten sodium chloride. • Cl- ions anode • Cl-(l) Cl2(g) + 2e- • Oxidized • Creates chlorine gas • Na+ ions cathode • Na+(l) + e- Na(l) • Reduced • Creates pure liquid sodium
Electrolytic Cells • What is the primary purpose of electrolysis? • Used in mining and refining processes to remove certain metals out of molten ore
Compare and Contrast Voltaic Cell Electrolytic Cell • Creates electricity • Spontaneous • Exothermic • Anode (-) and Cathode (+) • Oxidation at anode • Reduction at cathode • Two solutions • Contain a salt bridge • Creates electricity • Non-spontaneous (battery) • Endothermic • Anode (+) and Cathode (-) • Oxidation at anode • Reduction at cathode • One solution • No salt bridge