Oxidation is the loss of electrons whereas reduction is the gain of electrons

Note that oxidation and reduction are defined in different terms. This is one of the convenient ways to understand and remember when handling oxidation-reduction (redox) reactions. The reactions in which oxidation and reduction occur simultaneously are called redox reactions. Oxidation and reduction are two half-reactions of complete redox reactions.

The problem is often to remember the difference between the two. A made-up acronym “OIL-RIG” can be useful here, which says, “Oxidation is loss and reduction is gain”. Be sure to remember that this mnemonic is applicable only in terms of hydrogen and electrons.

Oxidation vs. Reduction - Remembering mnemonic - acronym - OIL RIG

Oxidation vs Reduction

Oxidation Reduction
Oxidation is a chemical process involving the loss of electrons by a molecule, atom, or ion, leading to the increase in the oxidation state of the chemical species Reduction is a chemical process involving the gain of electrons by a molecule, atom, or ion, that leads to a decrease in oxidation states of the chemical species
Oxidation is addition of oxygen Reduction is the removal of oxygen
Oxidation involves the loss of electrons Reduction involves the gain of electrons
Oxidation is the removal of hydrogen Reduction is the addition of hydrogen
There is an increase in oxidation state There is a decrease in the oxidation state
Oxidation is caused by oxidizing agents Reduction is caused by reducing agents
An example of oxidation is the oxidation of glucose during respiration An example of reduction is the reduction of carbon dioxide during photosynthesis

Related topics

Explanation of oxidation vs reduction

Oxidation and reduction in terms of oxygen transfer

The term oxidation was originally used in 1787 by Antoine Lavoisier, to describe the combination reaction involving oxygen. The addition of oxygen is therefore called oxidation.

For example, the combination of calcium and oxygen in the below reaction is oxidation.

2Ca(s) + O2 (g) → 2CaO (s)

The term reduction, originated from Latin meaning “leading back to” involves the loss of oxygen. For the first time, Justus von Liebig stated that reduction is the removal of oxygen and the addition of hydrogen.

For example, the metal oxides upon reaction with carbon monoxide lead back to their respective metals. This involves the removal of oxygen.

CO + CaO → CO2 + Ca

Oxidation and reduction in terms of hydrogen transfer

Oxidation is the loss of hydrogen while reduction is the gain of hydrogen.

For example,

In the below reaction, ethanol is oxidized to ethanal and can be identified by the loss of hydrogen.


Ethanal can be reduced back to ethanol by the addition of hydrogen.


Remember that such reactions require proper oxidizing and reducing agents.

“An oxidizing agent oxidizes the other substance in a reaction while getting reduced itself. Whereas a reducing agent reduces the other substance and gets oxidized itself.”

Oxidation and reduction in terms of transfer of electrons

Oxidation is the loss of electrons and reduction is the gain of electrons. For example,

CuO + Mg → Cu + MgO

In this reaction, magnesium is a reducing agent. It reduces copper (II) ion to neutral copper by donating two electrons. Magnesium becomes magnesium ion after losing those two electrons.

In short,

  • Copper gains electrons and is reduced.
  • Magnesium loses electrons and is oxidized.

Oxidation and reduction in terms of oxidation state

This category of oxidation and reduction is similar to that of the transfer of electrons. Loss and gain of electrons result in a change of oxidation state. This means we can find out whether oxidation or reduction has occurred with respect to the changes in oxidation states.

“Oxidation is the increase in the oxidation state. On the other hand, reduction is the decrease in the oxidation state.”

CuO + Mg → Cu + MgO

In the above reaction, copper gains two electrons resulting in a decrease in oxidation state, so, copper is being reduced. Magnesium loses two electrons, resulting in an increase in its oxidation state. Thus, magnesium is said to be oxidized.

Key takeaway(s)

Oxidation vs. Reduction: How to Remember the Difference?

Concepts Berg

How to remember oxidation and reduction?

“OIL RIG” is a made-up acronym that stands for oxidation is loss and reduction is gain of electrons.

Give an example of reduction and oxidation?

CO2(g) + H2(g) → CO(g) + H2O(g)

In this reaction, CO2 is reduced when it reacts with hydrogen as the oxidation state of the carbon decreases from +4 to +2. While hydrogen is oxidized in this reaction as its oxidation state increases from 0 to +1.

What is the difference between oxygenation and oxidation?

Oxygenation is the addition of molecular oxygen to any system whereas oxidation is the loss of electron, loss of hydrogen as well as gain of oxygen.

What is the difference between oxidation and synthesis?

Synthesis is the process of making different substances in a chemical reaction using different techniques. Oxidation is one such reaction where electron loss is involved.

Is an oxidation reaction endothermic or exothermic?

If an element is being oxidized, then the process should be endothermic such as in combustion. This is because energy must be provided to eject electrons from atoms. So, all the ionization energies are positive values.

However, not all oxidations are endothermic. For example, in redox reactions, oxidation and reduction occur simultaneously. They are typically exothermic.

What is the difference between oxidizing agents and reducing agents?

The oxidizing agents gain electrons and are reduced while the reducing agents lose electrons and are oxidized in a chemical reaction.

What is the difference between oxidation and combustion?

Combustion is the complete oxidation of organic compounds in presence of oxygen gas whereas oxidation is the addition of oxygen to an element or a compound.

What is the difference between oxidation and corrosion?

Corrosion is a type of oxidation brought on by wet weather conditions, whereas oxidation occurs naturally when air (oxygen) reacts with metals or compounds.

Reference books

  • General Chemistry, Principles, and Structure, by James E. Brandy (St. John’s University, Jamaica, New York) and Gerard E. Humiston (Widener University, West Chester, Pennsylvania) – [SI version, Prepared by Henry Heikkinen (University of Maryland, USA)]

Additional Resources