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Chapter 19

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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Chapter 19

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  1. Electrochemistry Chapter 19

  2. Redox Revisited

  3. Redox Revisited

  4. Redox Revisited

  5. Redox Revisited

  6. Redox Revisited

  7. Redox Revisited

  8. Redox Revisited

  9. Reactivity Revisited

  10. Reactivity Revisited

  11. Reactivity Revisited TIME

  12. Reactivity Revisited

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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 - +

  21. Voltaic Cells

  22. Voltaic Cells

  23. Voltaic Cells

  24. 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

  25. Electrolytic Cells • How is an electrical current produced? • The ions in the electrolyte solution move towards the electrode with the opposite charge

  26. 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

  27. Electrolytic Cells

  28. 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

  29. Electrolytic Cells • What is the primary purpose of electrolysis? • Used in mining and refining processes to remove certain metals out of molten ore

  30. Electrolytic Cells

  31. 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

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