What is a redox reaction in chemistry?

A redox reaction in chemistry is a type of chemical reaction that involves a transfer of electrons between two species.

In more detail, the term 'redox' is an abbreviation for reduction-oxidation. This refers to two simultaneous reactions that occur in any redox process - reduction and oxidation. Oxidation is the loss of electrons from a substance, while reduction is the gain of electrons by a substance. These reactions always occur together, hence the term 'redox' reaction.

For example, consider the reaction between magnesium and oxygen to form magnesium oxide. In this reaction, magnesium loses two electrons to become a magnesium ion (Mg2+). This is an oxidation process because magnesium is losing electrons. On the other hand, oxygen gains these two electrons to become an oxide ion (O2-). This is a reduction process because oxygen is gaining electrons.

In a redox reaction, the substance that loses electrons (in this case, magnesium) is known as the reducing agent, because it causes the other substance to be reduced. Conversely, the substance that gains electrons (in this case, oxygen) is known as the oxidising agent, because it causes the other substance to be oxidised.

Redox reactions are fundamental to many natural and industrial processes. They are involved in processes such as respiration, photosynthesis, combustion, and corrosion. They also play a key role in the operation of batteries and fuel cells. Understanding redox reactions is therefore crucial to understanding many aspects of chemistry.