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Topic: Electrochemical Cells

Topic: Electrochemical Cells. Do Now: Quiz – Half -reactions. Electrochemistry – the study of the relationship between chemical potential energy and electrical energy . All this occurs Via flow of electrons. Chemical rxns can produce electricity OR

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Topic: Electrochemical Cells

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  1. Topic: Electrochemical Cells Do Now: Quiz – Half -reactions

  2. Electrochemistry – the study of the relationship between chemical potential energy and electrical energy

  3. All this occurs Via flow of electrons • Chemical rxns can produce electricity OR • Electrical energy can be used carry out chemical reactions A Chemical reactions can generate electrical energy if it occurs spontaneously

  4. Single Replacement reactions are Redox Rxns • Use table J to predict if the reaction is spontaneous • Any metal will donate its electrons to the ion of any metal below it. = Spontaneous • Any nonmetal will steal electrons from the ion of any nonmetal below it. = Spontaneous

  5. One beaker Contains: • Zn(NO3)2 & Cu • AgNO3& Cu • Which beaker is which…how can you tell?!

  6. If in a galvanic cell, will the following generate electricity (hint: they must be spontaneous) • Li + AlCl3 • Cs + CuCl2  • I2 + NaCl  • Cl2 + KBr  • Fe + CaBr2  • Mg + Sr(NO3)2  • F2 + MgCl2  Yes Yes No Yes No No Yes

  7. How does a spontaneous reaction generate electricity? Electrochemical Cells • Used when the chemical rxn is spontaneous • It produces electricity (energy) via flow of electrons through a wire therefore is exothermic • Oxidation and Reduction Reaction have to be separated • AKA voltaic cell or galvanic cell

  8. Remember the lab SR labAgNO3 + Cu  _______ +_______ +5 0 +1 +5 -2 0 -2 +1 CuNO3 Ag Was this spontaneous? Was this a redox? So why didn’t we produce electricity? yes Yes, Ag was Reduced & Cu was Oxidized Half reactions weren’t separated

  9. Electrochemical Cell Requirements • 2 half-cells containing aqueous solution & an electrode • Need to be connected by a wire for the electrons to flow through. • Need to be connected by a salt bridgeto maintain electrical neutrality. (if electrons are moving ions need to move also) aq aq

  10. Electrode Surface at which oxidation or reduction half-reaction occurs. Anode – Oxidation The anode = location for the oxidation half-reaction. Reduction – Cathode The cathode = location for the reduction half-reaction.

  11. MOVIE CLIP • MEMORIZE • An OxAte a FatRed Cat • Anode oxidation • Fat (getting bigger) Reduction Cathode YUMMY

  12. A(s) + BX(aq)  B(s) + AX(aq) • One electrode will gain mass (B) and one electrode will dissolve (A). • The concentration of metal ions will increase in one solution (making AX) & decrease in one solution (using up BX).

  13. How do you know which electrode is which? • Use Table J to predict which electrode is the anode and which electrode is the cathode. • Anode = Oxidation = Electron Donor • higher in Table J. • Cathode = Reduction = Electron Acceptor • lower in Table J.

  14. Label anode and cathode anode cathode

  15. e-  e-  e-  e-  e-  e- • Electrons flow from Anode to Cathode • Positive Ions flow from Anode to Cathode via salt bridge (too offset the negative electrons) • Which direction would the negative ions flow? +  +  +  + anode cathode Anode = site of oxidation =getting smaller cathode = site of reduction =getting larger

  16. When the cells reach equilibriumvoltage = 0no more electrical current

  17. What’s wrong with this picture?

  18. Now you tryCreate an galvanic (electrochemical) cell with Al and Pb and AlNO3 and Pb(NO3)2Label anode and cathode(Use Table J), direction of electron flow in wire, direction of positive ion flow in salt bridge, positive electrode, negative electrode. Pb Al

  19. Create an galvanic (electrochemical) cell with Al and Pb and AlNO3 and Pb(NO3)2Label anode and cathode(Use Table J), direction of electron flow in wire, direction of positive ion flow in salt bridge, positive electrode, negative electrode. e-  e-  e-  e-  e-  e- Pb Al Al cathode anode Al+3& NO3-1 Pb+2& NO3-1

  20. What half-reactions occured?REMEMBER Al got smaller and Pb got bigger Al  Al+3 + 3e- Pb+2 + 2e-  Pb Al was the anode, it was oxidized, it lost e- Pb got bigger. How? By gaining electrons. The Pb+2 ions gained 2 e- to make Pb.

  21. Overall Rxn 2(Al  Al+3 + 3e-) 3(Pb+2 + 2e-  Pb) + _______________________ 2Al + 3Pb+2 2Al+3 + 3Pb

  22. 2Al + 3Pb+2 2Al+3 + 3Pb • Which electrode is losing mass? • Which electrode is gaining mass? • What’s happening to the [Al+3]? • What’s happening to the [Pb+2]? Al because now Al+3 ions in solution Pb, Pb+2 gains 2 e- an makes solid Pb Increasing Decreasing

  23. Notation for Cells ZnZn+2Cu+2Cu

  24. Application: Batteries

  25. Dry Cell

  26. Mercury battery

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