It depends on which oxide is produced. The most common result is Al2O3.
So the first step is to find the oxide produced. Having done that your equation becomes.
Al + O2 ==> Al2O3 You have to pick a Common Multiple for O3 and O2. That would be your next set. In other words you want something that 3 and 2 will divide into evenly. That would be 6 The 3 on O3 divides into 6 evenly as 2
Al + O2 ===> 2Al2O3
Turn your attention to O2 on the left. 2 goes into 6 evenly. The answer is 3
Al + 3O2 ====> 2Al2O3
That leaves Al. The right side has 2 * 2 infront and behind the Aluminum That's 4
The balanced equation is
4Al + 3O2 ===> 2Al2O3
I have given you the entire procedure for balancing an equation. What you do first is a decision made by the person teaching the course.
