1. Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: 1981

2. Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: Zn (s) + 2 NH 4 + (aq) + 2MnO 2(s) Zn 2+ (aq) + Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O 1982

3. Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: Zn (s) + 2 NH 4 + (aq) + 2MnO 2(s) Zn 2+ (aq) + Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O The voltage produced is ~ 1.5 V. This cell loses its ability to function rather rapidly under heavy current drain – products don’t diffuse away from the electrode very quickly. Advantage: low price. 1983

4. In cell notation, the dry cell is: 1984

5. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C 1985

6. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. 1986

7. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: 1987

8. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: 1988

9. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by 1989

10. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) 1990

11. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 1991

12. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 2MnO 2(s) + H 2 O + e - MnO(OH) (s) + OH - (aq) 1992

13. In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 2MnO 2(s) + H 2 O + e - MnO(OH) (s) + OH - (aq) followed by: NH 4 + (aq) + OH - (aq) NH 3(aq) + H 2 O 1993

14. The mercury battery The mercury battery: 1994

15. The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. 1995

16. The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. 1996

17. The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- 1997

18. The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- Cathode: HgO (s) + H 2 O (l) + 2e - Hg (l) + 2 OH - (aq) 1998

19. The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- Cathode: HgO (s) + H 2 O (l) + 2e - Hg (l) + 2 OH - (aq) Overall reaction: Zn(Hg) (s) + HgO (s) ZnO (s) + Hg (l) 1999

20. The voltage is 1.35 V. The overall cell reaction involves only solid substances. This battery has a longer shelf-life compared to the dry cell. Disadvantage: toxicity of discarded batteries. Environmental impact. 2000

21. The nickel-cadmium storage cell (nicad battery) 2001

22. The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. 2002

23. The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- 2003

24. The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) 2004

25. The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) Overall reaction: Cd (s) + NiO (s) + 2H 2 O (l) Cd(OH) 2(s) + Ni(OH) 2(s) 2005

26. The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) Overall reaction: Cd (s) + NiO (s) + 2H 2 O (l) Cd(OH) 2(s) + Ni(OH) 2(s) Disadvantages: Cd is toxic; environmental impact; higher cost. Advantage, can be recharged. 2006

27. The lead-acid storage battery 2007

28. The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. 2008

29. The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- 2009

30. The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- Cathode: PbO 2(s) + 4H + (aq) + SO 4 2- (aq) + 2e - PbSO 4(s) + 2 H 2 O (l) 2010

31. The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- Cathode: PbO 2(s) + 4H + (aq) + SO 4 2- (aq) + 2e - PbSO 4(s) + 2 H 2 O (l) Overall reaction: Pb (s) + 2H 2 SO 4(aq) + PbO 2(s) 2 PbSO 4(s) + 2 H 2 O (l) 2011

32. Voltage produced is ~ 12 V (2 V from each cell). 2012

33. Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. 2013

34. Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. 2014

35. Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. 2015

36. Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. For the battery to function properly, the electrolyte must be fully conducting. 2016

37. Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. For the battery to function properly, the electrolyte must be fully conducting. However, the ions move much more slowly in a viscous medium – leads to lower power output from the battery. 2017

38. Fuel Cells 2018

39. Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. 2019

40. Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. e.g. CH 4 + 2O 2 CO 2 + 2 H 2 O + heat 2020

41. Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. e.g. CH 4 + 2O 2 CO 2 + 2 H 2 O + heat To generate electricity, heat produced by the reaction is first used to convert water to steam, which then drives a turbine that drives a generator. 2021

42. An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. 2022

43. An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. 2023

44. An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. This can be accomplished in a fuel cell. A fuel cell consists of an electrolyte solution, such as H 2 SO 4 or NaOH and two inert electrodes. 2024

45. An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. This can be accomplished in a fuel cell. A fuel cell consists of an electrolyte solution, such as H 2 SO 4 or NaOH and two inert electrodes. H 2 and O 2 are bubbled through the anode and cathode compartments: 2025

46. Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- 2026

47. Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) 2027

48. Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) Overall reaction: 2H 2(g) + O 2(g) 2H 2 O (l) 2028

49. Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) Overall reaction: 2H 2(g) + O 2(g) 2H 2 O (l) A potential difference is established between the two electrodes. The overall reaction exactly reverses the electrolysis of H 2 O. 2029

50. The electrodes serve a double purpose. First, they serve as electrical conductors. 2030

51. The electrodes serve a double purpose. First, they serve as electrical conductors. Second, the electrodes provide the necessary surfaces for the initial decomposition of the molecules into atomic species, prior to electron transfer. 2031

52. The electrodes serve a double purpose. First, they serve as electrical conductors. Second, the electrodes provide the necessary surfaces for the initial decomposition of the molecules into atomic species, prior to electron transfer. They are electrocatalysts. Metals such as Pt, Ni, Rh are good electrocatalysts. 2032

53. 2033

54. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. 2034

55. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. 2035

56. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- 2036

57. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) 2037

58. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) Overall reaction: C 3 H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2 O (l) 2038

59. In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) Overall reaction: C 3 H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2 O (l) Note the overall reaction is identical to burning propane in dioxygen. 2039

60. Fuel cells differ from batteries in that the former do not store chemical energy. 2040