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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
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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
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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
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In cell notation, the dry cell is: 1984
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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
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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
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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
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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
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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
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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
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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
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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
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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
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The mercury battery The mercury battery: 1994
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The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. 1995
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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
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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
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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
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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
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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
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The nickel-cadmium storage cell (nicad battery) 2001
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The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. 2002
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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
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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
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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
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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
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The lead-acid storage battery 2007
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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
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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
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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
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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
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Voltage produced is ~ 12 V (2 V from each cell). 2012
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Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. 2013
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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
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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
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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
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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
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Fuel Cells 2018
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Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. 2019
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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
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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
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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
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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
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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
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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
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Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- 2026
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Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) 2027
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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
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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
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The electrodes serve a double purpose. First, they serve as electrical conductors. 2030
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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
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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
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In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. 2034
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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
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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
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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
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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
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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
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Fuel cells differ from batteries in that the former do not store chemical energy. 2040
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