Balance: Fe + O2 = Fe2O3

In order to balance Fe + O2 = Fe2O3 you'll need to watch out for two things.

First, be sure to count all of Fe and O atoms on each side of the chemical equation. Once you know how many of each type of atom you have you can only change the coefficients (the numbers in front of atoms or compounds) in order to balance the equation.

Second, when you balance the equation it is easier to change the coefficient in front of Fe2O3 first in order to get an even number of Oxygen atoms. As a general rule, this makes balancing equations much easier.

Drawing/writing done in Adobe Illustrator 6.0. Screen capture done with Camtasia Studio 4.0. Done on a Microsoft Surface Pro 3.