Balancing Chemical Equations A Review

A chemical reaction can be described by an equation. In the equation, the reactants, the chemicals that react, are on the left. The chemicals they produce, the products, are on the right. The chemicals can be represented by either their names or their element symbols. The two sides are separated by an arrow.

Just by looking at this you can tell that something is not right. For example: Aluminum + Oxygen  Aluminum Oxide Al + O2  Al2O3 Just by looking at this you can tell that something is not right. Let’s count the atoms on each side: Al: 1  Al: 2 O: 2  O: 3

Al + O2  Al2O3 We can balance the equation by multiplying the atoms by different amounts. Let’s start with the aluminum atoms. Multiply the left side by two so that it will equal the right. 2Al + O2  Al2O3 Now our Al atoms our balanced, but our oxygen atoms are not. What do we need to do to balance them?

2Al + O2  Al2O3 We need to figure out the lowest common denominator for both 2 and 3. What is it? That’s right, six. 2Al + 3O2  2Al2O3 But oh no, our aluminum atoms are no longer balanced! What do we need to do to the left side to balance them? We simply need to change the 2 on the left to a 4 and our equation is balanced. 4Al + 3O2  2Al2O3

With all that said, remember this helpful hint: Balance the elements last! In equations you will find two things, elements and molecules. When possible, always balance the lone elements last. It will make life a lot easier. Try this one: CO2 + H2 CH4 + H2O

Also, you can never change subscripts, only coefficients! Don’t use 1 as a coefficient or subscript – the one is invisible!