How to balance an unbalance equation?

The first step is to write down the unbalanced chemical equation. If you're lucky, this will be given to you. If you're told to balance a chemical equation and only given the names of the products and reactants, you'll need to either look them up or apply rules of naming compounds to determine their formulas.

Let's practice using a reaction from real life, the rusting of iron in the air. To write the reaction, you need to identify the reactants (iron and oxygen) and the products (rust). Next, write the unbalanced chemical equation:

Fe + O2 → Fe2O3

Note the reactants always go on the left side of the arrow. A "plus" sign separates them. Next, there is an arrow indicating the direction of the reaction (reactants become products). The products are always on the right side of the arrow. The order in which you write the reactants and products is not important.