Difference Between Oxidation and Reduction

Oxidation and reduction are very important chemical reactions that take place in our surroundings all the time. When a covalent compound loses electronics, it becomes more positively charged and the process is called oxidation. Reduction is the opposite of oxidation as during the process a compound gains electronics and becomes more negatively charged. Reduction and oxidation are more commonly known as redox reaction as the transfer of electrons take place between chemical species (one loss and one gain).

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Oxidation vs Reduction

The difference between oxidation and reduction is that oxidation occurs when a chemical compound gains oxygen or loses hydrogen. This means the positive charge of the compound increases. On the other hand, the reduction is the opposite chemical reaction of oxidation where a chemical compound gains hydrogen or electrons and its negative charge increases. 

Oxidation vs Reduction

Oxidation is a chemical reaction where an atom or a molecule of a chemical species loses electrons (one or more) and becomes more positively charged. This chemical reaction increases the oxidation state and oxidation number of the chemical species that is undergoing oxidation. Oxygen is not always involved in the process of oxidation but sometimes it can cause the species to lose electrons. 

Reduction is a chemical reaction where an atom or a molecule of a chemical species gains electrons (one or more) and becomes more negatively charged. This chemical reaction decreases the oxidation state and oxidation number of the chemical species that is undergoing reduction. An oxidizing agent undergoes reduction as it oxidizes another chemical species involved in the reaction and reduces itself. 

Comparison Table

Parameters of ComparisonOxidationReduction
DefinitionOxidation refers to the gain of oxygen or loss of hydrogen from a compound. Reduction refers to the gain of hydrogen or loss of oxygen from a compound. 
ElectronsIn oxidation, a covalent compound releases electrons to the surrounding.In reduction, a covalent compound gains electrons from the surrounding.
AgentsThe common oxidizing agents are hydrogen peroxide and ozone. The common reducing agents are compounds that contain metals like potassium, barium, calcium, etc and an H ion.
ChargeIn oxidation positive charge increase as it loses electrons. In reduction negative charge increase as it gains electrons.  
Oxidation NumberOxidation leads to an increase in oxidation number.Reduction leads to a decrease in oxidation number.

What is Oxidation?

 The definition of oxidation has changed with time and the most recent one in simple words defines a process where a chemical species loses electrons and becomes more positive. Becoming more positive doesn’t necessarily mean having a positive charge. For example, if an ion X4- goes through the process of oxidation and loses two electrons it becomes X2-. This means that it becomes more positive as (-2) oxidation state is more than (-4) but it doesn’t carry a positive charge. 

If we go back to the history of chemical reactions, oxygen gas (O2) was one of the oldest known oxidizing agents. Since adding O2 in a chemical reaction led to the loss of electrons from another chemical species, oxidation was defined as a process where the presence of O2 was crucial. When iron combined with water to form iron oxide/rust this definition became more predominant. 

But, oxidation of a chemical species can or cannot contain oxygen gas necessarily. For example, when ethanol forms ethanal, it loses a hydrogen atom and the process is still considered oxidation. So, the presence of particularly oxygen gas is not required for oxidation. As long as a chemical species loses electrons and its oxidation state increases, oxidation takes place. 

Example of oxidation reaction: 2 KI + H2O2 →  I2 + 2 KOH   (oxidation of iodide). Here, the oxidation number of iodide changes from (-1) to (0).

What is Reduction?

Reduction is the opposite reaction of oxidation. This is because the electrons that are lost from a chemical species are obtained by another species which goes through reduction. During reduction, one or more than one electron is gained by an atom or a molecule and it becomes more negatively charged. When a species is going through reduction, the oxidation state of that compound decreases. 

Again, we might have confusion that a chemical compound or an ion will have a negative charge after reduction. For example, if an ion X4+ goes through the process of reduction and gains two electrons it becomes X2+. This means that it becomes more negative as (+2) oxidation state is less than (+4) but it doesn’t carry a negative charge. So, the process of reduction doesn’t necessarily mean a negative charge. Reduction signifies the gain of electrons and a reducing agent is responsible for that transfer of an electron to a species. 

Consider an example, ZnO  + C  → Zn  + CO  (reduction of zinc oxide). Here, the oxidation number of zinc changes from (+2) to (0). This means it has gained to electron and has been reduced. 

Main Differences Between Oxidation and Reduction

  1. Oxidation refers to the gain of oxygen or loss of hydrogen from a compound whereas reduction refers to the gain of hydrogen or loss of oxygen from a compound. 
  2. In oxidation, a covalent compound releases electrons to the surroundings whereas, in reduction, a covalent compound gains electrons from the surrounding.
  3. The common oxidizing agents are hydrogen peroxide and ozone whereas the common reducing agents are compounds that contain metals like potassium, barium, calcium, etc. and an H ion.
  4. In oxidation positive charge increase as it loses electrons whereas in reduction negative charge increase as it gains electrons.  
  5. Oxidation leads to an increase in oxidation number whereas reduction leads to a decrease in oxidation number.

References

  1. https://www.cabdirect.org/cabdirect/abstract/19811963339
  2. https://pubs.rsc.org/en/content/articlehtml/2015/dt/c5dt02612a
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