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Redox Reactions and Oxidation and Reduction

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Electrochemical process are redox reactions where energy is produced by a spontaneous reaction which produces electricity, otherwise electrical current stimulates a chemical reaction. In a redox reaction, an atom's oxidation state changes as a result of an electron transfer. 



Oxidation and Reduction 


The elements that are involved in an electrochemical reaction are characterized by the number of electrons each of them contain. The oxidation state of an ion is defined as the number of electrons that is has accepted or donated compared to its neutral state (which is defined as having an oxidation state of  0). If an atom or ion donates an electron in a reaction, then its oxidation state increases, if an element accepts an electron its oxidation state is decreased. 


When sodium reacts with chlorine, sodium gives up one electron and gains an oxidation state of +1. Chlorine accepts the electron and gains an oxidation state of 1. The sign of the oxidation state (positive/negative) corresponds to the value of each ion's electronic charge. They from an ionic bond because the attraction of the differently charged sodium and chlorine ions.


The loss of electrons in a substance is called oxidation, and the gain of electrons is reduction. 


Substance which lose electrons are also known as reducing agents, or reductants, and the substance which accepts the electron is known as the oxidizing agent, or oxidant. The oxidizing agent is always reduced in a reaction; the reducing agent is always oxidized. 


The gain of oxygen, loss of hydrogen and increase in oxidation number is also considered to be oxidation, while the opposite is true for reduction. 


A reaction in which both oxidation and reduction occurs is called a redox reaction. These are quite common; as one substance loses electrons the other substance accepts them. 


Oxidation requires an oxidant, and not surprisingly oxygen is an oxidant. Oxidation reactions don't necessarily need to involve oxygen. Even fire can be contained by an oxidant other than oxygen: fluorine fires are often unquenchable, as fluorine is an even stronger oxidant (it has a higher electronegativity) than oxygen.

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