Galvanic cell

Galvanische Zelle
galvanic cell

a galvanic cell or a galvanic element is a device for the transformation of spontaneously chemical into electricity. It is used in batteries and accumulators. Each combination of two different electrodes and electrolytes designates oneas galvanic element. They serve as Gleichspannungsquellen. The characteristic value is the Teilspannung/stamped tension. By the capacity of a galvanic element one understands the product of unloading amperage and - time.

The function of the galvanic cell is based on a redox reaction. Reduction and oxidation run off spatially separately in ever a half cell (half element). By connecting the two half cells with electron conductor and an ion leader the electric circuit is closed. The tension of the electric current can be computed by the Nernst equation, the tension hangsof the kind of the metal (electro-chemical electromotive series) and the concentration off. Contrary to the electrolysis, for example in the galvanotechnics, electricity can be won in the galvanic cell, while the electrolysis uses electricity. The anodethe cathode is negatively charged positively in a galvanic cell , while with the electrolysis the cathode is positively charged negatively and the anode.

The name decreases/goes back to the Italian physician Luigi Galvani .

In the proximity of Bagdad 1936 tongefässe becamefrom that 2. Century v. Chr. found, by which it is assumed that they could have been used for gold platings. They became under the name Bagdad battery admit.

examples

the Daniell element - a galvanic cell

always, if two differentMetals in an electrolytic solution are, develop a tension (galvanic cell). Beside the Daniell element (copper/zinc) can so e.g. also from copper and silver electrodes a galvanic element to be produced: The copper electrode dips the silver electrode into copper sulfate solution, into silver nitrate solution, and to be connected theseby a wire (electron conductor) with voltmeter and an ion leader.

At the copper electrode go more cu 2+ - ions in solution than cu ions again separating. Since copper delivers electrons to the electrode, if it goes into solution, loads itselfthe electrode negatively on (anode).

<math> {\ rm cu \ longrightarrow Cu^ {2+} + 2e^}< /math>

At the silver electrode separate against it more AG + - ions at the electrode as in solution go off. Therefore there are it at the silver electrode electron deficiency, loadsitself positively on (cathode).

<math> {\ rm 2Ag^ {+} + 2e^ \ longrightarrow 2Ag}< /math>

If the two electrodes are electrically leading connected, then a tension develops, but it flows still no river. The reason for it is that in the copper electrode a surplusat cu 2+ - and the solution develops itself for ions strongly positively up-loaded. Thus only so many copper ions go into solution, how separate at the same time at the electrode again. Something similar happens with the silver nitrate solution, only that itself here the solutionup-loads negatively, since from the neutral silver nitrate only the negatively charged nitrate ions remain remaining (while the positive silver ions to the silver electrode to deposit itself, by taking up there in each case three electrons).

Silver nitrate solution: C [NO 3 -] >> C [AG +]

copper sulfate solution: C [SO4 2] << therefore C [cu 2+


] are connected the electrode areas by a salt bridge, which is necessary at the electric circuit to close. The salt bridge is frequently a U-Rohr with electrolytes filled is, and its ends alsoa diaphragm or a diaphragm are provided. By the salt bridge the anion exchange is made around so the loading against of the individual cells to work. Another possibility the electrode areas to separate exists which in a semipermeable (halfpermeable) diaphragm likewise oneCharge reconciliation makes possible.

There are also galvanic cells with two equal half cells, which differ in their concentration, these calls one concentration cell.

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