- Industrial Electrochemistry by Derek Pletcher and Frank C. Walsh, Second Editions
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- Industrial Electrochemistry
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Close Figure Viewer. Browse All Figures Return to Figure. Previous Figure Next Figure. Email or Customer ID. Forgot password? Old Password. New Password. Password Changed Successfully Your password has been changed. Thus, Gibbs' theory becomes. Finally, Nernst divided through by the amount of charge transferred to arrive at a new equation which now bears his name:.
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A concentration cell is an electrochemical cell where the two electrodes are the same material, the electrolytes on the two half-cells involve the same ions, but the electrolyte concentration differs between the two half-cells. An example is an electrochemical cell, where two copper electrodes are submerged in two copper II sulfate solutions, whose concentrations are 0.
This type of cell will generate a potential that can be predicted by the Nernst equation. Both can undergo the same chemistry although the reaction proceeds in reverse at the anode. Reduction will take place in the cell's compartment where concentration is higher and oxidation will occur on the more dilute side. However, this value is only approximate, as reaction quotient is defined in terms of ion activities which can be approximated with the concentrations as calculated here.
The Nernst equation plays an important role in understanding electrical effects in cells and organelles. Such effects include nerve synapses and cardiac beat as well as the resting potential of a somatic cell. Many types of battery have been commercialized and represent an important practical application of electrochemistry. The zinc-manganese dioxide dry cell was the first portable, non-spillable battery type that made flashlights and other portable devices practical. The mercury battery using zinc and mercuric oxide provided higher levels of power and capacity than the original dry cell for early electronic devices, but has been phased out of common use due to the danger of mercury pollution from discarded cells.
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The lead—acid battery was the first practical secondary rechargeable battery that could have its capacity replenished from an external source. The electrochemical reaction that produced current was to a useful degree reversible, allowing electrical energy and chemical energy to be interchanged as needed. Common lead acid batteries contain a mixture of sulfuric acid and water, as well as lead plates.
One problem however is if left uncharged acid will crystallize within the lead plates of the battery rendering it useless. These batteries last an average of 3 years with daily use however it is not unheard of for a lead acid battery to still be functional after 7—10 years. Lead-acid cells continue to be widely used in automobiles.
Industrial Electrochemistry by Derek Pletcher and Frank C. Walsh, Second Editions
All the preceding types have water-based electrolytes, which limits the maximum voltage per cell. The freezing of water limits low temperature performance. The lithium battery , which does not and cannot use water in the electrolyte, provides improved performance over other types; a rechargeable lithium-ion battery is an essential part of many mobile devices. The flow battery , an experimental type, offers the option of vastly larger energy capacity because its reactants can be replenished from external reservoirs.
The fuel cell can turn the chemical energy bound in hydrocarbon gases or hydrogen directly into electrical energy with much higher efficiency than any combustion process; such devices have powered many spacecraft and are being applied to grid energy storage for the public power system. Corrosion is an electrochemical process, which reveals itself in rust or tarnish on metals like iron or copper and their respective alloys, steel and brass. For iron rust to occur the metal has to be in contact with oxygen and water , although chemical reactions for this process are relatively complex and not all of them are completely understood.
It is believed the causes are the following: Electron transfer reduction-oxidation. Iron III oxide hydrate is known as rust. An electric circuit is formed as passage of electrons and ions occurs, thus if an electrolyte is present it will facilitate oxidation , explaining why rusting is quicker in salt water.
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Coinage metals , such as copper and silver, slowly corrode through use. A patina of green-blue copper carbonate forms on the surface of copper with exposure to the water and carbon dioxide in the air. Silver coins or cutlery that are exposed to high sulfur foods such as eggs or the low levels of sulfur species in the air develop a layer of black Silver sulfide. Gold and platinum are extremely difficult to oxidize under normal circumstances, and require exposure to a powerful chemical oxidizing agent such as aqua regia.
Some common metals oxidize extremely rapidly in air. Titanium and aluminium oxidize instantaneously in contact with the oxygen in the air. These metals form an extremely thin layer of oxidized metal on the surface which bonds with the underlying metal.
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This thin layer of oxide protects the underlying layers of the metal from the air preventing the entire metal from oxidizing. These metals are used in applications where corrosion resistance is important. Iron , in contrast, has an oxide that forms in air and water, called rust , that does not bond with the iron and therefore does not stop the further oxidation of the iron.
Thus iron left exposed to air and water will continue to rust until all of the iron is oxided. Attempts to save a metal from becoming anodic are of two general types. Anodic regions dissolve and destroy the structural integrity of the metal.
Metals can be coated with paint or other less conductive metals passivation. This prevents the metal surface from being exposed to electrolytes. The region under the coating adjacent to the scratch acts as the anode of the reaction. A method commonly used to protect a structural metal is to attach a metal which is more anodic than the metal to be protected. This forces the structural metal to be cathodic , thus spared corrosion. It is called "sacrificial" because the anode dissolves and has to be replaced periodically. Zinc bars are attached to various locations on steel ship hulls to render the ship hull cathodic.
The zinc bars are replaced periodically.
Other metals, such as magnesium , would work very well but zinc is the least expensive useful metal. To protect pipelines, an ingot of buried or exposed magnesium or zinc is buried beside the pipeline and is connected electrically to the pipe above ground. The pipeline is forced to be a cathode and is protected from being oxidized and rusting. The magnesium anode is sacrificed. At intervals new ingots are buried to replace those lost.
The spontaneous redox reactions of a conventional battery produce electricity through the different chemical potentials of the cathode and anode in the electrolyte. However, electrolysis requires an external source of electrical energy to induce a chemical reaction, and this process takes place in a compartment called an electrolytic cell. When molten, the salt sodium chloride can be electrolyzed to yield metallic sodium and gaseous chlorine.
Industrially this process takes place in a special cell named Down's cell. The cell is connected to an electrical power supply, allowing electrons to migrate from the power supply to the electrolytic cell.
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Reactions that take place at Down's cell are the following: . This process can yield large amounts of metallic sodium and gaseous chlorine, and is widely used on mineral dressing and metallurgy industries. In order for this reaction to occur the power supply should provide at least a potential of 4 V. However, larger voltages must be used for this reaction to occur at a high rate. Water can be converted to its component elemental gasses, H 2 and O 2 through the application of an external voltage. Water doesn't decompose into hydrogen and oxygen spontaneously as the Gibbs free energy for the process at standard conditions is about The decomposition of water into hydrogen and oxygen can be performed in an electrolytic cell.
In it, a pair of inert electrodes usually made of platinum immersed in water act as anode and cathode in the electrolytic process. The electrolysis starts with the application of an external voltage between the electrodes. This process will not occur except at extremely high voltages without an electrolyte such as sodium chloride or sulfuric acid most used 0. Bubbles from the gases will be seen near both electrodes. The following half reactions describe the process mentioned above:.
Although strong acids may be used in the apparatus, the reaction will not net consume the acid. Electrolysis in an aqueous solution is a similar process as mentioned in electrolysis of water. However, it is considered to be a complex process because the contents in solution have to be analyzed in half reactions , whether reduced or oxidized.
The presence of water in a solution of sodium chloride must be examined in respect to its reduction and oxidation in both electrodes. Usually, water is electrolysed as mentioned in electrolysis of water yielding gaseous oxygen in the anode and gaseous hydrogen in the cathode. The following half reactions describes the process mentioned: . Reaction 1 is discarded as it has the most negative value on standard reduction potential thus making it less thermodynamically favorable in the process. When comparing the reduction potentials in reactions 2 and 4, the reduction of chloride ion is favored.