Question

Rust (Fe2O3) forms on abandoned cars such as the one in this photo through a series of reactions between iron in the car and oxygen in the atmosphere. The unbalanced chemical equation for this reaction is $$

Answer 1

When undergoing chemical reactions, atoms change their oxidation state or oxidation number, which simply means that they give or recieve electrons. Important things that we need to know is that oxidation is a loss of electrons (which means that oxidation number is increasing or becoming more positive) while, on the other hand, reduction is gaining of electrons, which of course means that oxidation number decreases.

Another important thing to know is that oxidation number of free elements in elementary state is always 0. So, in our equation Fe and O2 both have oxidation number 0. In Fe2O3, oxidation number of Fe is +3 and of O is -2.

So, that means that iron went from 0 to +3 and oxygen went from 0 to -2

and.

Since Fe increased its number that means it oxidized, while O2 reduced because its number decreased.