Oxidation Reaction vs Reduction Reaction
 

Oxidation and reduction reactions are interrelated. Where one substance is oxidized another substance reduces. Therefore, these reactions are jointly known as redox reactions.

Oxidation Reaction

Originally oxidation reactions were identified as the reactions wherein oxygen gas participates. Here, oxygen combines with another molecule to produce an oxide. In this reaction, oxygen undergoes reduction and the other substance undergoes oxidation. Therefore, basically oxidation reaction is adding oxygen to another substance. For example, in the following reaction, hydrogen undergoes oxidation and, therefore, oxygen atom is added to hydrogen forming water.

2H2 + O2 -> 2H2O

Another way to describe oxidation is as loss of hydrogen. There are some occasions where it is hard to describe oxidation as adding oxygen. For example, in the following reaction oxygen has added to both carbon and hydrogen but only carbon has undergone oxidation. In this instance, oxidation can be described by saying it is the loss of hydrogen. As hydrogens have removed from methane when producing carbon dioxide, carbon there has been oxidized.

CH4 + 2O2 -> CO2 + 2H2O

Another alternative approach to describe oxidation is as losing of electrons. This approach can be used to explain chemical reactions, where we can’t see an oxide formation or hydrogen losing. So, even when there is no oxygen, we can explain oxidation using this approach. For example in the following reaction, magnesium has converted to magnesium ions.  Since, magnesium has lost two electrons it has undergone oxidation and chlorine gas is the oxidizing agent.

Mg + Cl2 -> Mg2+ + 2Cl–

Oxidation state helps to identify the atoms which have undergone oxidation. According to the IUPAC definition, oxidation state is “a measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have.” Oxidation state is an integer value, and it can be either positive, negative or zero. Oxidation state of an atom is subjected to change upon chemical reaction. If the oxidation state is increasing, then the atom is said to be oxidized. As in the above reaction, magnesium has zero oxidation state and magnesium ion has +2 oxidation state. Since the oxidation number has increased, magnesium has oxidized.

Reduction Reaction

Reduction is the opposite of oxidizing. In terms of oxygen transfer, in the reduction reactions, oxygens are lost. In terms of hydrogen transfer, reduction reactions take place when hydrogen is gained. For instance, in the above example between methane and oxygen, oxygen has reduced because it has gained hydrogen. In terms of electron transfer, reduction is gaining electrons. So according to the above example, chlorine is reduced.

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