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REDOX EQM Primary Cell, Secondary Cell & Fuel Cell

p.01. C. Y. Yeung (CHW, 2009). e.g. Zinc-carbon Cell. cathode. anode. 06. REDOX EQM Primary Cell, Secondary Cell & Fuel Cell. Primary Cell: non-rechargable cell. absorb H 2. electrolyte. p.02. Zn - C Cell. Anode: Zn(s)  Zn 2+ (aq) + 2e -.

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REDOX EQM Primary Cell, Secondary Cell & Fuel Cell

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  1. p.01 C. Y. Yeung (CHW, 2009) e.g. Zinc-carbon Cell cathode anode 06 REDOX EQM Primary Cell, Secondary Cell & Fuel Cell Primary Cell: non-rechargable cell absorb H2 electrolyte

  2. p.02 Zn - C Cell Anode: Zn(s)  Zn2+(aq) + 2e- Cathode: 2NH4+(aq) + 2e- 2NH3(aq) + H2(g) 2MnO2(s) + H2(g)  Mn2O3(s) + H2O(l) Cathode: 2NH4+(aq) + 2MnO2(s) + 2e- 2NH3(aq) + Mn2O3(s) + H2O(l) Cell equation: Zn(s) + 2NH4+(aq) + 2MnO2(s)  Zn2+(aq) + 2NH3(aq) + Mn2O3(s) + H2O(l) Cell Diagram : Zn(s) | Zn2+(aq)  [2MnO2(s) + 2NH4+(aq)] , [2NH3(aq) + Mn2O3(s) + H2O(l)] | C(graphite) ~ Primary cells are not rechargable, because some of the products of the electrochemical rxns are no longer available in the system (i.e. H2). The reverse rxn cannot occur upon charging.

  3. p.03 p. 235 Q.23 HKALE 2001 Paper 1 Q.4(b)

  4. p.04 p. 230 Q.5 HKALE 1995 Paper 2 Q.3(c)

  5. p.05 p. 230 Q.5 HKALE 1995 Paper 2 Q.3(c) --- continue

  6. p.06 e- e- Pb H2SO4(l) [electrolyte] PbSO4 0 PbO2 coated with PbSO4(s) +2 Pb Pb coated with PbO2(s) V +4 PbO2(s) PbSO4(s) reduction Pb + SO42- PbSO4 + 2e- Pb(s) PbO2 + SO42- + 4H++ 2e- PbSO4 + 2H2O oxidation H2SO4(l) Secondary Cell: rechargable cell e.g. Lead-Acid Accumulator discharging CATHODE ANODE Cell Diagram: [Pb(s)+ SO42-(aq)] | PbSO4(s) | H2SO4(l) | [PbO2(s)+ SO42-(aq) + 4H+(aq)], [PbSO4(s) + 2H2O(l)] | Pb(s)

  7. p.07 e- e- PbO2(s) PbSO4(s) coated with PbSO4(s) coated with PbSO4(s) Pb(s) oxidation reduction PbSO4 + 2e- Pb + SO42- H2SO4(l) PbSO4 + 2H2O  PbO2 + SO42- + 4H++ 2e- Lead-Acid Accumulator is RECHARGABLE, because … ~ All the products of the electrochemical rxns remain in the system. The reverse rxn can occur upon charging. charging i.e. PbO2(s) and Pb(s) are regenerated. ANODE CATHODE

  8. p.08 Lead-Acid Accumulator

  9. p.09 p. 232 Q.12 HKALE 1998 Paper 2 Q.4(a)

  10. p.10 Give out ELECTRICITY through Redox Rxns. Give out HEAT through Combustion. 2 H2(g) + O2(g) 2 H2O(l) Advantages: Less Energy Loss + Compact + Less Pollution Fuel Cell : Combustion & Redox Rxn Use FUEL to give out ELECTRICITY throughRedox Rxns !! ELECTROLYSIS (Input = Electricity) COMBUSTION (Output = Heat) REDOX (Output = Electricity????)

  11. p.11 How does FUEL CELL work? (1) Step 1: Step 2: (catalyst = Pt or Ni)

  12. p.12 How does FUEL CELL work? (2) Step 3: Step 4:

  13. p.13 How does FUEL CELL work? (3) Step 5:

  14. p.14 When Acid is used as electrolyte (catalysed by Ni) Anode: H2(g)  2H+(aq) + 2e- (catalysed by NiO) Cathode: O2(g) + 4H+(aq) + 4e- 2H2O(l) When Alkali is used as electrolyte (catalysed by Ni) Anode: H2(g) +2OH-(aq)  2H2O(l) + 2e- (catalysed by NiO) Cathode: O2(g) + 2H2O(l) + 4e- 4OH-(aq) How does FUEL CELL work? (4) Cell Diagram: Ni(s) | H2(g) | 2H+(aq)  [O2(g) + 4H+(aq)], 2H2O(l)] | NiO(s) Cell Diagram: Ni(s) | [H2(g) + 2OH-(aq)], 2H2O(l)  [O2(g) + 2H2O(l)], 4OH-(aq) | NiO(s)

  15. p.15 Fuel Cells ** Advantages of Fuel Cell? Article Reading: A hybrid between “Generator” & “Battery” -- the “Fuel Cell”

  16. p.16 p. 236 Q.27(a) HKALE 2002 Paper 2 Q.3(b)

  17. p.17 Next …. Eqm Completed! Book 2 finished! Book 3A p.2 – 26 (**p.8-9 **) Assignment Article Reading [due date: 25/5 (Mon)] p.229 Q.12, 23 [due date: 25/5 (Mon)]

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