1. Electrochemical cells: utilize relationship between chemical potential energy & electrical energy

2. Everyday Redox Reactions battery to start car prevent corrosion of metals cleaning with bleach (oxidizing agent) Na, Al, Cl prepared or purified by redox reactions breathing O 2  H 2 O and CO 2

3. Redox Reactions synthesis rxns decomposition rxns SR rxns DR rxns are NOT redox rxns! all are redox rxns

4. Predicting Redox Reactions Table J: used to predict if given redox reaction will occur single metaldonatessingle metal donates electrons to ions of metals below itself (oxidaizes) single non-metaltakessingle non-metal takes electrons from ion of non-metals below itself (reduces)

5. Predicting Redox Reactions A + BX  B + AX If metal A above metal B (Table J): rxn is spontaneous If metal A below metal B: rxn is NOT spontaneous

6. X + AY  Y + AX If non-metal X above non-metal Y (Table J): rxn is spontaneous If non-metal X below non-metal Y: rxn is NOT spontaneous

7. Spontaneous or not? Li + AlCl 3  Cs + CuCl 2  I 2 + NaCl  Cl 2 + KBr  Fe + CaBr 2  Mg + Sr(NO 3 ) 2  F 2 + MgCl 2 yes yes no yes no no yes

8. placed Cu(s) in beakers: one contains Zn(NO 3 ) 2 (aq) other contains AgNO 3 (aq) Which beaker contains which ions? contains Zn ions? & contains Ag ions? A B

9. Overview of Electrochemistry TWO kinds of Electrochemical Cells

10. 1. galvanic or Voltaic 1. galvanic or Voltaic cells: electrochemical cells (Regents: electrochemical cells) –use spontaneous rxn to produce flow of electrons (electricity) –exothermic

11. 2. electrolytic cells: –use flow of electrons (electricity) to force non-spontaneous rxn to occur –endothermic

12. Vocabulary galvanic cell Voltaic cell electrochemical cell Board of Regents considers all 3 as electrochemical cells - not exactly accurate

13. galvanic cells/Voltaic cells (NYS: electrochemical cells) use spontaneous SR redox rxn: produce flow of electrons electrons flow from oxidized substance to reduced substance

14. Cell Set-up components arranged so e - forced to flow through wire when e - travel through a wire, can make them do work: light a bulb, ring a buzzer oxidation & reduction reactions must be separated physically

15. Parts of a galvanic/Voltaic Cell 2 half-cells: - one for oxidation rxn - one for oxidation rxn - one for reduction rxn - one for reduction rxn each ½ cell consists of: aq soln: container with aq soln: +/- ions electrodeelectrode –surface where e - transfer takes place –wire connects 2 electrodes –salt bridge connects 2 solutions

16. How much work can you get out of this reaction? can measure voltage by allowing electrons to travel through voltmeter galvanic cell is a battery –not easy battery to transport or use in real-life applications

17. electrode: surfaces at which oxidation or reduction half-reaction occur anode: oxidation surface decreases in mass cathode: reduction surface increases in mass

18. An OxRed Cat An Ox ate a Red Cat Anode – OxidationAnode – Oxidation –anode: location for oxidation half-rxn Reduction – CathodeReduction – Cathode –cathode: location for reduction half-rxn

19. Anode / Cathode how know which electrode is which? Table J:Table J: use to predict which electrode is anode and which electrode is cathode

20. Anode Anode = Oxidation = Electron Donor –anode composed of metal HIGHER on Table J

21. Cathode Cathode = Reduction = Electron Acceptor – cathode composed of metal LOWER on Table J

22. Zn above Cu: Zn is anode; Cu is cathode cathode

23. Direction of e - Flow (through wire): Anode → Cathode

24. Direction of (+) Ion Flow (salt bridge): Anode → Cathode

25. negative electrode negative electrode (anode): e - originate here: Zn electrode in this picture Zn electrode decreases in mass Zn +2 ions increase in concen aq solns contain ions of same element as electrode 

26. positive electrode positive electrode (cathode): e - attracted here: Cu electrode in this picture Cu electrode increases in mass Cu +2 ions decrease in concen aq solns contain ions of same element as electrode 

27. Salt Bridge allows migration of ions between half-cells –necessary to maintain electrical neutrality reaction can not proceed without salt bridge

28. Half-Reactions ox: Zn  Zn +2 + 2e - red: Cu +2 + 2e -  Cu _________________________ Zn + Cu +2  Zn +2 + Cu Which electrode is dissolving? Which electrode is gaining mass? Which species is increasing its concen? Which species is getting more dilute?Zn Zn +2 Cu Cu +2

29. When the reaction reaches equilibrium voltage is 0! –electrons no longer flow

30. Construct Galvanic Cell with Al & Pb Use Table J to identify anode & cathode Draw Cell: put in electrodes & solutions Label: –anode –cathode –positive electrode –negative electrode, –direction of electron flow in wire –direction of positive ion flow in salt bridge[remember: negative electrode: where electrons originate, positive electrode: attracts electrons]

31. Electron flow  Al: anode Pb:cathode wire Salt bridge Al +3 & NO 3 -1 Pb +2 & NO 3 -1 Positive ion flow  (-)  Oxidation: Al  Al +3 + 3e - Reduction: Pb +2 + 2e -  Pb

32. Overall Rxn (Al  Al +3 + 3e - ) + (Pb +2 + 2e -  Pb) _____________________________ 2Al + 3Pb +2  2Al +3 + 3Pb 2Al + 3Pb +2 + 6e -  2Al +3 + 3Pb + 6e - 2 3

33. Application: Batteries

34. Dry Cell Battery

35. Mercury Battery

36. Corrosion to resist corrosion: coat one metal with stronger more durable metal

37. What’s wrong with this picture?