1. 1 Electrochemistry

2. 2 Electricity Movt of electrons Movt of electrons Movt of electrons through wire connecting 2 half-reactions  electrochemical cell Movt of electrons through wire connecting 2 half-reactions  electrochemical cell Also called voltaic or galvanic cell Also called voltaic or galvanic cell Cell produces current from spont rxn Cell produces current from spont rxn Ex: copper in soln of AgNO 3 is spont Ex: copper in soln of AgNO 3 is spont Electrolytic cell uses electrical current to drive a non-spont chemical rxn Electrolytic cell uses electrical current to drive a non-spont chemical rxn

3. 3 Voltaic cell Solid Zn in zinc ion soln = half- cell Solid Zn in zinc ion soln = half- cell Likewise, Cu/Cu ion soln Likewise, Cu/Cu ion soln Wire attached to each solid Wire attached to each solid Salt bridge = Salt bridge = 1. contains electrolytes, 1. contains electrolytes, 2. connects 2 half-cells, 2. connects 2 half-cells, 3. anions flow to neutralize accumulated cations at anode and vice-versa (completes circuit) 3. anions flow to neutralize accumulated cations at anode and vice-versa (completes circuit) “An Ox” = anode oxidation “An Ox” = anode oxidation Has negative charge cuz releases e - Has negative charge cuz releases e - “Red Cat” = reduction cathode “Red Cat” = reduction cathode Has positive charge cuz takes up e - Has positive charge cuz takes up e -

4. 4 Electrical current Measured in amperes (A) Measured in amperes (A) 1 A = 6.242 x 10 18 e - /s 1 A = 6.242 x 10 18 e - /s Electric current driven by diff in potential E/unit of charge Electric current driven by diff in potential E/unit of charge Pot diff (electromotive force or emf) = volt (V) Pot diff (electromotive force or emf) = volt (V) 1 V = J/C 1 V = J/C

5. 5 Batteries Dry-cell batteries Dry-cell batteries Don’t contain large amts of water Don’t contain large amts of water Duracell Duracell Anode: Zn oxidized Anode: Zn oxidized Cathode: 2MnO 2(s) + 2NH 4 + (aq) + 2e -  Mn 2 O 3(s) + 2NH 3(g) + H 2 O (l) Cathode: 2MnO 2(s) + 2NH 4 + (aq) + 2e -  Mn 2 O 3(s) + 2NH 3(g) + H 2 O (l) Cathode is Carbon-rod immersed in moist (acidic) paste of MnO 2 that houses NH 4 Cl Cathode is Carbon-rod immersed in moist (acidic) paste of MnO 2 that houses NH 4 Cl 1.5 V 1.5 V

6. 6 Batteries More common dry-cell type: alkaline battery More common dry-cell type: alkaline battery Anode: Zn (s) + 2OH - (aq)  Zn(OH) 2(s) + 2e - Anode: Zn (s) + 2OH - (aq)  Zn(OH) 2(s) + 2e - Cathode: Cathode: 2MnO 2(s) + 2H 2 O (l) + 2e -  2MnO(OH) (s) + 2OH - (aq) 2MnO 2(s) + 2H 2 O (l) + 2e -  2MnO(OH) (s) + 2OH - (aq) Longer shelf-life, “live” longer Longer shelf-life, “live” longer Cathode in basic paste Cathode in basic paste

7. 7 Batteries Lead-acid storage batteries Lead-acid storage batteries In cars In cars 6 electrochemical cells (2V) in series 6 electrochemical cells (2V) in series Anode: Pb (s) + HSO 4 - (aq)  PbSO 4(s) + H + (aq) + 2e - Anode: Pb (s) + HSO 4 - (aq)  PbSO 4(s) + H + (aq) + 2e - Cathode: Cathode: PbO 2(s) + HSO 4 - (aq) + 3H + (aq) + 2e -  PbSO 4(s) + 2H 2 O (l) PbO 2(s) + HSO 4 - (aq) + 3H + (aq) + 2e -  PbSO 4(s) + 2H 2 O (l) In 30% soln of sulfuric acid In 30% soln of sulfuric acid If dead, due to excess PbSO 4 covering electrode surfaces If dead, due to excess PbSO 4 covering electrode surfaces Re-charge (reverse rxn)  converts PbSO 4 to Pb and PbO 2 Re-charge (reverse rxn)  converts PbSO 4 to Pb and PbO 2

8. 8 Rechargeable batteries Ni-Cd Ni-Cd Anode: Cd (s) + 2OH - (aq)  Cd(OH) 2(s) + 2e - Anode: Cd (s) + 2OH - (aq)  Cd(OH) 2(s) + 2e - Cathode: Cathode: 2NiO(OH) (s) + 2H 2 O (l) + 2e -  2Ni(OH) 2(s) + 2OH - (aq) 2NiO(OH) (s) + 2H 2 O (l) + 2e -  2Ni(OH) 2(s) + 2OH - (aq) KOH, usually, used KOH, usually, used 1.30 V 1.30 V Reverse rxn recharges battery Reverse rxn recharges battery Excess recharging  electrolysis of water Excess recharging  electrolysis of water EXPLOSION!!! EXPLOSION!!! Muhahahaha! Muhahahaha!

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10. 10 Rechargeable batteries Cd toxic Cd toxic Ni-MH Ni-MH Hybrid car batteries: high energy density Hybrid car batteries: high energy density Same cathode rxn Same cathode rxn Anode: MH (s) + OH - (aq)  M (s) + H 2 O (l) + e - Anode: MH (s) + OH - (aq)  M (s) + H 2 O (l) + e - Commonly, M = AB 5, where A is rare earth mixture of La, Ce, Nd, Pr, and B is Ni, Co, Mn, and/or Mn Commonly, M = AB 5, where A is rare earth mixture of La, Ce, Nd, Pr, and B is Ni, Co, Mn, and/or Mn Very few use AB 2, where A = Ti and/or V Very few use AB 2, where A = Ti and/or V

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12. 12 Rechargeable batteries Anode made of graphite w/incorporated Li-ions btwn carbon layers Anode made of graphite w/incorporated Li-ions btwn carbon layers Ions spontaneously migrate to cathode Ions spontaneously migrate to cathode Cathode = LiCoO 2 or LiMn 2 O 4 Cathode = LiCoO 2 or LiMn 2 O 4 Transition metal reduced Transition metal reduced Used in laptop computers, cell phones, digital cameras Used in laptop computers, cell phones, digital cameras Light weight and high E density Light weight and high E density

13. 13 Fuel cell Reactants flow through battery Reactants flow through battery Undergo redox rxn Undergo redox rxn Generate electricity Generate electricity Hydrogen-oxygen fuel cell Hydrogen-oxygen fuel cell Anode: 2H 2(g) + 4OH - (aq)  4H 2 O (l) + 4e - Anode: 2H 2(g) + 4OH - (aq)  4H 2 O (l) + 4e - Cathode: O 2(g) + 2H 2 O (l) + 4e -  4OH - (aq) Cathode: O 2(g) + 2H 2 O (l) + 4e -  4OH - (aq) Used in space-shuttle program Used in space-shuttle program

14. 14 Electrolysis Electrical current used to drive nonspont redox rxn Electrical current used to drive nonspont redox rxn In electrolytic cell In electrolytic cell Electrolysis of water Electrolysis of water Metal plating: silver coated on metal, jewelry, etc. Metal plating: silver coated on metal, jewelry, etc.