Difference Between Oxidation and Reduction

Main Difference – Oxidation vs Reduction

Oxidation and reduction are the two half reactions of redox reactions. A redox reaction is a chemical reaction that occurs through the electron exchange between atoms. The main difference between oxidation and reduction is that oxidation is the increasing of oxidation state of an atom whereas reduction is the decreasing of the oxidation state of an atom.

Key Areas Covered

1. What is Oxidation
      – Definition, Mechanism, Examples
2. What is Reduction
      – Definition, Mechanism, Examples
3. What is the Difference Between Oxidation and Reduction
      – Comparison of Key Differences

Key Terms: Oxidation, Oxidation State, Oxidizing Agent, Redox Reaction, Reducing Agent, ReductionDifference Between Oxidation and Reduction - Comparison Summary

What is Oxidation

oxidation can be defined as the loss of electrons from an atom, molecule or an ion. This loss of electrons causes the oxidation state of the chemical species to be increased. Since an oxidation reaction releases electrons, there should be an electron accepting species. Therefore, the oxidation reaction is a half reaction of a major reaction. The oxidation of a chemical species is given as the change of its oxidation states. Oxidation state is a number with positive (+) or negative (-) symbol that indicates the loss or gain of electrons by a particular atom, molecule or an ion.

In the past, the term oxidation was given the definition “the addition of oxygen to a compound.” This was because oxygen was the only known oxidizing agent at that time. However, this definition is no longer accurate since there are many more oxidation reactions that occur in the absence of oxygen. For example, the reaction between Magnesium (Mg) and Hydrochloric acid (HCl) involves no oxygen, but it is a redox reaction that includes the oxidation of Mg into Mg2+. The following example shows the oxidation and reduction reactions in a redox reaction.

Difference Between Oxidation and Reduction

Figure 01: Oxidation of Mg by the addition of Oxygen to Mg. Two electrons are released from Mg, and one oxygen atom obtains two electrons.

There is another historical definition for oxidation involving Hydrogen. That is, oxidation is the process of losing H+ ions. This is also not accurate because there are many reactions that occur without the release of H+ ions.

Difference Between Oxidation and Reduction_Figure 02

Figure 02: The oxidation of alcohol group into Carboxylic acid group

An oxidation always increases the oxidation state of a chemical species due to the loss of electrons. This loss of electrons causes the charge of an atom or molecule to be changed.

Oxidation Mechanism

Oxidation can occur in four different ways depending on the change of the oxidation state.

1. From Zero to Positive Oxidation State

A molecule or an atom that has no electrical charge (neutral) can be oxidized. The oxidation always increases the oxidation state. Therefore, the new oxidation state of the atom would be a positive value.

Difference Between Oxidation and Reduction_Figure 03

Figure 03: oxidation of Fe (0) to Fe (+3)

2. From Negative to Positive Oxidation State

An atom in a negative oxidation state can be oxidized to a positive oxidation state.

Difference Between Oxidation and Reduction_Figure 04

Figure 04: The oxidation of S (-2) into S (+6) oxidation state

3. From Negative to Zero Oxidation State

Difference Between Oxidation and Reduction_Figure 05

Figure 05: The oxidation of O (-2) to O2 (0)

4. Increase of Positive Oxidation State

This type of oxidation reactions is mostly included with transition metal elements since these metal elements can hold several oxidation states and they show up to +7 oxidation state due to the presence of d orbitals.

Difference Between Oxidation and Reduction_Figure 06

Figure 06: The oxidation of Fe (+2) to Fe (+3)

A neutral atom is composed of protons (positively charged) in the nucleus and electrons (negatively charged) around the nucleus. The positive charge of the nucleus is balanced by the negative charges of electrons. But when an electron is removed from this system, there’s no negative charge to neutralize the corresponding positive charge. Then the atom gets a positive charge. Therefore, the oxidation always increases the positive characteristics of atoms.

What is Reduction

Reduction can be defined as the gain of electrons from an atom, molecule or an ion. This gain of electrons causes the oxidation state of the chemical species to decrease because the reduction creates an extra negative electrical charge in atoms. In order to obtain electrons from outside, there should be an electron donating species. Therefore, the reduction is a chemical reaction that takes place during redox reactions. Reduction reaction is a half reaction.

Reduction Mechanism

Reduction also can occur in four ways as follows.

1. From Zero to Negative Oxidation State

For example, in the formation of oxides, the oxidation state of O2 is zero and it is decreased to -2 due to the addition of new electrons.

Difference Between Oxidation and Reduction_Reduction Mechanism_01

Figure 07: Reduction of oxygen

2. From Positive to Negative Oxidation State

Elements that can hold positive, as well as negative oxidation states, can undergo this type of reduction reactions.

Difference Between Oxidation and Reduction_Reduction Mechanism_02

Figure 08: Reduction of N (+3) to N (-3)

3. From Positive to Zero Oxidation State

Difference Between Oxidation and Reduction_Reduction Mechanism_03

Figure 09: The reduction of Ag+

4. Decrease of Negative Oxidation State

Main Difference - Oxidation vs Reduction

Figure 10: Reduction of O (-2) to O (-1)

Generally, oxygen atoms in compounds have -2 oxidation state. But in peroxides, there are two oxygen atoms bonded to each other. Both atoms have the same electronegativity. Therefore, the oxidation state of both atoms would be -2. Then one oxygen atom has -1 oxidation state.

Difference Between Oxidation and Reduction

Definition

Oxidation: Oxidation can be defined as the loss of electrons from an atom, molecule or an ion.

Reduction: Reduction can be defined as the gain of electrons from an atom, molecule or an ion.

Change of Oxidation State

Oxidation: The oxidation state increases in oxidation.

Reduction:  The oxidation state decreases in reduction.

Exchange of Electrons

Oxidation: Oxidation reactions release electrons to the surrounding.

Reduction: Reduction reactions obtain electrons from the surrounding.

Change of Electrical Charge

Oxidation: Oxidation causes the increase of positive charge of a chemical species.

Reduction: Reduction causes the increase of negative charge of a chemical species.

Chemical Species Involved

Oxidation: Oxidation occurs in reducing agents.

Reduction: Reduction occurs in oxidizing agents.

Conclusion

Oxidation and reduction are the two half reactions of redox reactions. The main difference between oxidation and reduction is that oxidation is the increasing of the oxidation state of an atom whereas reduction is the decreasing of the oxidation state of an atom.

References:

1.Helmenstine, Anne Marie. “What Is Reduction in Chemistry?” ThoughtCo. N.p., n.d. Web. Available here. 06 July 2017. 
2.”What is oxidation.” Study.com. Study.com, n.d. Web. Available here. 06 July 2017. 

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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