Electrochemical cell
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A typical electrochemical cell setup. |
An
electrochemical cell is a setup used for creating an
electromotive force (voltage) in a conductor separating two reactions. The current is caused by the reactions releasing and accepting
electrons in to the different ends of the conductor. The most common example of an electrochemical cell is a standard 1.5-volt
battery.
In each
half-cell is a chemical undergoing either
oxidation or reduction. In a full electrochemical cell, one side must be losing electrons (oxidation) in to its
electrode while the other half-cell gains electrons (reduction). If the atoms/ions involved in the reaction are
metal, the same metal is used for each electrode. If the
atoms/
ions involved in the reaction at each half-cell are not metal, obviously no electrode can be constructed out of it. Nonreactive metals such as
platinum are used as a substitute (as in the
standard hydrogen electrode). Finally, a
salt bridge is necessary to provide electrical contact between the cells—but without the solutions mixing. This can simply be a strip of
filter paper soaked in saturated potassium nitrate (V) solution.
Different choices of substances for each half-cell results in varying potential differences. Each reaction is undergoing an
equilibrium reaction between different oxidation states of the ions—when equilibrium is reached the cell cannot provide further voltage. In the half-cell which is undergoing oxidation, the closer the equilibrium lies to the ion/atom with the more positive oxidation state the more potential this reaction will provide. Similarly, in the reduction reaction, the further the equilibrium lies to the ion/atom with the more
negative oxidation state the higher the potential.
This potential can be predicted quantitatively through the use of
electrode potentials (the voltage measured when the substance is connected to
hydrogen). The difference in voltage between electrode potentials gives a prediction for the potential measured.
*
galvanic cell*
electrochemical potential*
Nickel Cadmium battery*
Alkaline battery*
Concentration cell
