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Modules Open College - e-Learning Content Library
Galvanic Element
This module illustrates the movement of molecules and redox reactions that occur in galvanic elements, explaining the conversion of chemical reaction energy into the energy of electric current.
Consider what happens to an atom of zinc that belongs to a zinc electrode structure. This atom gives away 2 electrons and enters the solution. 2 electrons leave the zinc electrode via the wires, thus removing the negative charge that could prevent further dissolving of the electrode. The electrons reach the copper electrode, and a copper ion receives the 2 electrons and settles, now as a neutral atom, at the copper electrode. Charge balance is restored, since the electrons have passed from one part of the galvanic element to the other. After the two electrons have left zinc for copper, traveling via the external circuit, in the right section of the model (zinc electrode location), either the two potassium ions go to the salt bridge (ion conductor), or two chlorine ions leave the salt bridge. Electric neutrality of the barrel with zinc electrode is restored in either case. Similarly, upon the electrons' arrival at the copper electrode, either potassium ions leave the salt bridge, or chlorine ions enter it.
Note that the salt bridge separating anode and cathode areas of the galvanic element (sometimes a porous barrier is used in the capacity of this bridge) eliminates the thermal option of redox reaction: Zn + Cu2+ = Zn2+ + Cu. By ensuring the closure of the circuit, this condition makes electrons pass from anode (zinc) to cathode (copper) via an external circuit (electron conductor), with the release of energy occurring at the load. If the external circuit is open, the voltage on the electrodes (the potential difference) is equal to the EMF of the galvanic element.

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