Utilizes relationship between chemical potential energy & electrical energy

1. Utilizes relationship between chemical potential energy & electrical energy

2. Redox Reactions • Need battery to start car • Prevent corrosion • Bleach is an oxidizing agent • Na, Al, Cl prepared or purified by redox reactions • Breathing • O2 H2O and CO2

3. Redox Reactions • Synthesis • Decomposition • Single Replacement • Double Replacement are not redox rxn! Redox

4. Predicting Redox Reactions • Use Table J to predict if a given redox reaction will occur • Any metal will donate its electronsto the ion of any metal below it • Any nonmetal will stealelectrons from the ion of any nonmetal below it

5. Predicting Single Replacement Redox Reactions Element + Compound  New Element + New Compound If the element is above the swapable ion, the reaction is spontaneous If the element is below the swapable ion, the reaction is not spontaneous

6. Predicting Redox Reactions A + BX  B + AX A & B are metals If metal A is above metal B in Table J, the reaction is spontaneous X + AY  Y + AX • X & Y are nonmetals If nonmetal X is above nonmetal Y in Table J, the reaction is spontaneous

7. Yes Yes No Yes No No Yes Spontaneous or not? • Li + AlCl3 • Cs + CuCl2 • I2 + NaCl  • Cl2 + KBr • Fe + CaBr2 • Mg + Sr(NO3)2 • F2 + MgCl2

8. Started with: Zn(NO3)2 & Cu and AgNO3 & Cu Which beaker had the Zn ions & which had the Ag ions?

9. Overview of Electrochemistry • TWO kinds of cells (kind of opposites): 1. Galvanic or Voltaic (NYS – Electrochemical) Use a spontaneous rxn to produce a flow of electrons (electricity) = Exothermic 2. Electrolytic Use a flow of electrons (electricity) to force a nonspontaneous rxn to occur =Endothermic

10. Anode Cathode Galvanic Voltaic Electrochemical Electrolytic Salt bridge Vocabulary • Redox • Half-reaction • Oxidation • Reduction • Cell • Half-Cell • Electrode

11. Electrochemical Cells • Use spontaneous SR redox reaction to produce flow of electrons • Electrons flow from oxidized substance to reduced substance • Names: Galvanic cells, voltaic cells, or electrochemical cells (NYS)

12. Electrochemical Cells • Redox rxn arranged so electrons are forced to flow through a wire • When electrons travel through a wire, can make them do work - light a bulb,ring a buzzer • oxidation & reduction reactions must be separated physically

13. Half-Cell • Place where each half-reactions takes place • two ½ cells needed for complete redox rxn • need to be connected by awirefor the electrons to flow through • need to be connected by asalt bridgeto maintain electrical neutrality

14. Schematic of Galvanic/Voltaic Cell

15. Parts of a Galvanic/Voltaic Cell • 2 half-cells: oxidation & reduction • Each half-cell consists of: • container with aqueous solution & electrode (surface at which the electron transfer takes place) • Wire connects electrodes • Salt bridge connects solutions

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

17. Electrode Surface at which oxidation or reduction half-reaction occurs: Anode & Cathode

18. An Ox Ate a Red Cat • Anode – Oxidation • the anode = location for the oxidation half-reaction • Reduction – Cathode • the cathode = location for the reduction half-reaction

19. Anode / Cathode • How do you know which electrode is which? • Use Table J to predict which electrode is the anode and which electrode is the cathode

20. Anode • Anode = Oxidation = Electron Donor • anode is metal that’s higher on Table J

21. Cathode • Cathode = Reduction = Electron Acceptor • cathode is metal that’s lower on Table J

22. Zn is above Cu, Zn is anode

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

24. Direction of Positive Ion Flow (salt bridge): Direction of Electron Flow(through wire): Anode → Cathode Anode →Cathode

25. Positive & Negative Electrode • Negative electrode (anode) is where electrons originate • here it’s the Zn electrode • Positive electrode (cathode) is electrode that attracts electrons • here it’s the Cu electrode

26. Aqueous Solution • Solution containing ions of the same element as the electrode • Cu electrode: • Solution: Cu(NO3)3 or CuSO4 • Zn electrode: • Solution: Zn(NO3)2 or ZnSO4

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

28. A(s) + BX(aq)  B(s) + AX(aq) • SR rxn occurs during operation of galvanic/voltaic cell • One electrode gains mass (B) and one electrode dissolves (A) • concen of metal ions ↑ in one soln (making AX) &↓ in other soln (using up BX)

29. _________________________ Zn + Cu+2 Zn+2 + Cu Zn Zn+2 Half-Reactions Zn  Zn+2 + 2e- Cu+2 + 2e- Cu Which electrode is dissolving? Which species is increasing its mass?

30. Cu Cu+2 Zn + Cu+2 Zn+2 + Cu • Which electrode is gaining mass? • Which species is getting more dilute?

31. When the reaction reaches equilibrium • The voltage goes to 0!

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

33. Electron flow  wire Positive ion flow  Pb = cathode Al = anode Salt bridge (-)  Pb+2 & NO3-1 Al+3 & NO3-1

34. Al metal is the electrode: it’s dissolving • Al+3 ions go into the solution What are half-reactions? Al  Al+3 + 3e- Pb+2 + 2e- Pb • Pb+2 ions are in the solution • Ions pick up 2 electrons & platetogetheron surface of Pb electrode as Pb0

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

36. Al Pb Increasing Decreasing 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]?

37. Application: Batteries

38. Dry Cell

39. Mercury battery

40. Application: Corrosion

41. Corrosion Prevention

42. What’s wrong with this picture?