Introduction: Redox reactions
If you have seen a piece of rusty metal then you have seen the end result of a redox reaction (iron and oxygen forming iron oxide). Redox reactions are also used in electrochemistry and in biological reactions.
When some reactions occur, an exchange of electrons takes place. It is this exchange of electrons that leads to the change in charge that we noted in another lesson from the tutorial on reactions in aqueous solution. When an atom gains electrons it becomes more negative and when it loses electrons it becomes more positive.
Oxidation is the loss of electrons from an atom, while reduction is the gain of electrons by an atom. In a reaction these two processes occur together so that one element or compound gains electrons while the other element or compound loses electrons. This is why we call this a redox reaction. It is a short way of saying reduction-oxidation reaction!
You can remember this by using OiLRiG: Oxidation is Loss Reduction is Gain.
Oxidation is the loss of electrons by a molecule, atom or ion.
Reduction is the gain of electrons by a molecule, atom or ion.
Before we look at redox reactions we need to first learn how to tell if a reaction is a redox reaction. In grade 10 you learnt that a redox reaction involves a change in the charge on an atom. Now we will look at why this change in charge occurs.