Redox reactions occur every day in the world around us. They may be subtle, such as a common breathalyzer test, or have catastrophic consequences such as the burning down of a building. They may be spontaneous (and happen instantly) or non-spontaneous (and happen over a long period of time). Whatever the form, redox reactions are some of the most important chemical reactions in our known world.
The word redox is a portmanteau of the words reduction and oxidation. These are two half reactions, each involving the gain or loss of electrons from a single entity.
Although counter-intuitive, a reduction reaction involves one entity gaining electrons to acquire a more negative charge. For example, 2 moles of Chlorine ions (2Cl-) can be reduced to Chlorine Gas (Cl2) by adding 2 electrons (2e-). The reason for the apparent misnomer of reduction is because in ancient times, chemists noticed a decrease in mass of the substance that was reduced, and thus termed the half-reaction as according to how the mass changed.
Again, while counterintuitive, the half-reaction of oxidation does not, in fact, demand that oxygen be added to a substance. Looking back at historical chemistry, we see that the most common occurrence of this phenomenon was when oxygen (O2) was added to a metal such as Iron (Fe) to create rust, or what we now know to be iron (II) oxide (FeO). Little did the ancient chemists know that the oxygen was actually losing some of its electrons when it formed an ionic bond with the iron. Modern chemists have now defined oxidation as any half reaction that involves the loss of electrons by an entity.
When writing half-reactions, it is common to deal with only a single entity, such as the Chlorine ions or Oxygen gas in the above examples. These can be written out like a normal chemical equation, except with a number of electrons as either a reactant or a product. Note that for an oxidation, the electrons will be a product, and for a reduction the electrons will be a reactant.
We can combine the two half-reactions into one full Redox reaction by ensuring that the same number of electrons are lost and gained in each separate half reactant. Simply multiply both equations by a coefficient in order to ascertain the correct quantities. Then, write all the products on one side of the equation, and all the reactants on the other, with all the electrons canceling out.
Redox reactions affect our everyday lives, and the transfer of electrons can have profound implications towards contemporary society.