Redox reactions are reactions that involves the transfer of electrons between chemicals. Redox reactions comprise of two main components; oxidation and reduction. Both of these reactions occurs simultaneously.

Oxidation is the process when a reactant loses an electron.

i.e. $Zn(s)\longrightarrow Zn^{2+}(aq)+2e^{-}$

Reduction is the process when a reactant gains an electron.

i.e. $Cu^{2+}(aq)+2e^{-}\longrightarrow Cu(s)$

It is important to note that substances that cause oxidation to occur are known as oxidising agents/oxidants however it itself is getting reduced. Similarly, substances known as reductants cause reduction to occur but it is getting oxidised. From the example of oxidation and reduction above, assuming they were both in the same system, the Zn(s) would be the reductant because it is causing the reductant reaction to occur and it itself is getting oxidised. The Cu2+ would be oxidant as it is causing the oxidation reaction to occur and it itself is getting reduced.

The way redox questions are solved are first by simply writing out the half equations for both the oxidant and reductant, eliminating e-s and finally adding up the two equations together as 1 overall balanced equation. Steps involved in writing out half equations include:

• Balance all elements other than hydrogen and oxygen in the half equation.
• Balance the oxygen atoms by adding H2.
• Balance hydrogen atoms by adding H+
• Balance the charge on both sides of the equation by adding e