The Concept of Redox Reactions (Reduction-Oxidation) & Examples

The Concept of Redox Reactions (Reduction-Oxidation) & Examples

Reduction and reductant are two words that are related to each other. These two words are often found in chemistry lessons at the Junior High School (SMP) and Senior High School (SMA) levels. For lay people, these words are rarely heard and their use is also rare, even though both words have meanings that occur in everyday life. However, many people do not know. So, what is meant by a redox reaction? Check out the following definition, concept, and examples.

Definition of Redox Reactions

Redox reactions are an abbreviation of reduction and oxidation reactions that occur in an electrochemical process. In general, redox is a term that explains the change in oxidation numbers of atoms in a chemical reaction.

This can be a simple redox process, such as the oxidation of carbon to produce carbon dioxide, or the reduction of carbon by hydrogen to produce methane (CH4), or it can be a complex process such as the oxidation of sugar in the human body through a series of complicated electron transfers. The term redox comes from two concepts, namely reduction and oxidation. These concepts can be easily explained as follows:

• Oxidation is the release of electrons by a molecule, ion, or atom.
• Reduction is the addition of electrons by a molecule, ion, or atom.

Although quite appropriate for use in various purposes, the above explanation is not always correct. Oxidation and reduction refer precisely to changes in oxidation number because the actual transfer of electrons does not always occur.

Therefore, oxidation is interpreted as an increase in oxidation number, while reduction is a decrease in oxidation number. In practice, electron transfer always changes the oxidation number, but there are many reactions that are classified as redox, even though there is no electron transfer in the reaction, for example those involving covalent bonds. Non-redox reactions that do not involve changes in formal charge are metathesis reactions.

The Concept of Redox Reactions

Reduction and oxidation (redox) reactions have concepts based on the transfer of oxygen, electrons, and oxidation numbers. 3 basic concepts of redox reactions are as follows:

Redox reactions based on oxygen atom transfer

The first basic concept of redox reactions is based on oxygen transfer. Where the redox reaction occurs from the binding and release of oxygen from two reacting substances. Oxidation reactions are oxygen binding reactions, while reduction reactions are the release of oxygen. An example of a redox reaction based on oxygen atom transfer is the reaction between carbon and mercury (II) oxide, namely: C + 2 HgO → CO2 + Hg

Redox reactions based on electron transfer

The second basic concept of redox reactions is a redox reaction based on electron transfer. Oxidation reactions are reactions that release electrons while reduction reactions bind or obtain electrons. Substances that release electrons are called reductants. Substances that bind electrons are called oxidizing agents. Examples of redox reactions based on electron transfer are as follows: Cu (s) + 2Ag+ (aq) → Cu 2+ (aq) + 2 Ag (s)

Redox reactions based on hydrogen transfer

The last basic concept of redox reactions is redox reactions based on hydrogen transfer. Where redox reactions become reactions formed from oxidation reactions due to the loss of hydrogen and reduction reactions due to the binding of hydrogen. Examples of redox reactions based on hydrogen transfer are the reactions of ammonia and bromine as follows: 2NH3 + 3Br2 → N2 + 6HBr.

Examples of Redox Reactions Based on the Concept

Examples of Redox Reactions Based on the Involvement of Oxygen Atoms

In this concept, the Oxidation process means the reaction of elements that bind oxygen. For example, as follows.

Example 1: the rusting process of metal and iron because the iron element binds oxygen either from the air or from water. The reaction is: 4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s)

Example 2: combustion of methane gas (CH4) produces carbon dioxide gas and water vapor. The reaction is: CH4 (g) + O2 (g) → CO2 (g) + 2H2O (g)

Example 3: oxidation of glucose in the human body through the respiration process. Glucose is broken down into simple compounds such as carbon dioxide and water. The reaction is: C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g)

Example 4: an apple that is peeled and then left in the open air will turn brown in color, because the glucose reacts with oxygen.

Meanwhile, in the same concept, Reduction is the release of oxygen due to the reaction of an element (the opposite of oxidation). An example of reduction is in the processing of iron ore (Fe2O3) into iron at high temperatures, using CO (carbon monoxide). In the reduction process in the processing of iron ore into iron, the reaction is: Fe2O3(s) + 3 CO(g) → 2Fe(s) + 3 CO2(g).

Example of the Concept of Redox Reaction Based on Electron Transfer

In a redox reaction, reduction and oxidation occur, so these two reactions occur simultaneously. This means that there is a substance that releases electrons and there is one that receives electrons in a redox reaction. Therefore, the name of the reaction is a reduction-oxidation reaction or redox reaction.

The general formula for redox reactions based on electron transfer is as follows:

A → An+ + n e (oxidation)

An+ + n e → A (reduction)

(n = number of electrons released or received)

For example, in the process of rusting iron, the following reactions can occur:

2 Fe → 2 Fe3+ + 6 e (oxidation) means 6 electrons are released by 2 iron atoms

3 O2 + 6 e → 3 O2- (reduction) means 3 oxygen atoms form the compound Fe2O3

Example of the Concept of Redox Reactions Based on Oxidation Numbers

This last example is an exception to the two concepts above, namely the existence of several redox reactions that cannot be explained even using the concept of oxygen involvement or electron transfer.

Chemistry experts create alternative concepts because there are many redox reactions that cannot be explained by the concept of oxygen binding or electron transfer. This alternative concept is called oxidation number changes. The explanation of this concept is: if in a reaction the oxidation number of an atom increases, the atom undergoes oxidation. If the oxidation number decreases, the atom will experience reduction.

To find out whether a reaction is a redox reaction or not, according to the concept of changes in oxidation numbers, the oxidation number of each atom must be known, both in the reactants and the reaction products.