Chemical equations are a considerable part of chemistry and science as a whole, which means you’ll spend time balancing chemical equations. Like fractions and algebra problems, these equations need to be balanced to use them properly. Typically, students learn how to write chemical equations in your 8th-grade science lessons, but if you want to get ahead of the class, or need a refresher, here are some easy steps to follow to help you learn how to balance chemical equations now.
What Is a Chemical Equation?
First, what is a chemical equation? Simply put, this equation is just an illustration of what happens during a chemical reaction. You have two sets of chemical symbols separated by an arrow. On the left-hand side, you have the reactants or the elements that are involved in the reaction. On the right-hand side, you have the products or the final result of the reaction.
Most chemical equations you see are unbalanced. This equation for the reaction that creates rust is the perfect example:
Fe + O₂ →Fe₂O₃
Your reactants are always separated by a plus sign, indicating that they are currently separate elements. A balanced equation helps you figure out the exact number of components needed to satisfy the requirements of the Law of Conservation of Mass.
Law of Conservation of Mass
The Law of Conservation of Mass is both simple and complex. It states that in a closed system, matter can’t be created or destroyed, merely changed.
Take a look at the iron oxide equation above. It’s unbalanced — you start with one iron and two oxygen but end up with two iron and three oxygen. Following the Law of Conservation of Mass, this can’t work.
There are six different types of chemical reactions, and the basics of balancing chemical equations are the same for each of them. For the sake of simplicity, we’re going to look at a combustion reaction — because who doesn’t love introducing a little fire to the equation?
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Step 1 — Identify the Elements
For this exercise, we’re going to look at the chemical reaction that takes place when you burn propane for your barbeque grill, producing carbon dioxide and water. The unbalanced formula looks like this:
C₃H₈ + O₂ →H₂O + CO₂
Our first step is to identify the elements that are present in this reaction. In this case, we have Carbon (C), Hydrogen (H) and Oxygen (O). C₃H₈ is propane, and the oxygen is present in the atmosphere and is necessary for the propane to burn. Write down the number of elements on each side of the balanced formula.
On the reactants side of this formula, we have three carbon atoms, eight hydrogen atoms and two oxygen atoms. On the products side, we have one carbon, two hydrogens and three oxygen.
Since hydrogen and oxygen are present in so many equations, these are balanced last.
Step 2 — Change the Coefficient
When you’re balancing chemical equations, you never change the subscripts — which are the small numbers to the right of each element. What you need to do to balance the equation is to add a coefficient to each component — a number to the left each piece.
First, you need to balance the carbon. Adding a coefficient of three to the CO₂ — 3 CO₂ — increases the number of carbon atoms to three, and the number of oxygen molecules to six. You get that by multiplying the subscript of the oxygen, which is two, by the coefficient of three.
The equation now looks like this:
C₃H₈ + O₂ →H₂O + 3 CO₂
Step 3 — Repeat Step Two
The next step is to repeat step number two and keep adding coefficients to balance the equation fully. Since all that’s left is the hydrogen and oxygen, it’s safe to move on to balance those two elements.
To balance the hydrogen, since you have eight hydrogen atoms on the reactants side of the equation, you’ll need a coefficient of four to bring up the number of hydrogen atoms from two to eight — multiply the coefficient of four by hydrogen’s subscript of two.
Now the equation looks like this:
C₃H₈ + O₂ → 4 H₂O + 3 CO₂
Next, we need to balance the oxygen, since there are 10 oxygen atoms on the product side and only two on the reactant side. This can be easily adjusted by adding a coefficient of five ahead of the oxygen molecule on the reactants side — the coefficient of five multiplied by the subscript of two gives you 10 oxygen atoms.
A fully balanced equation for burning propane looks like this:
C₃H₈ + 5 O₂ → 4 H₂O + 3 CO₂
Now both sides of the equation have three carbon atoms, eight hydrogen atoms and 10 oxygen atoms.
Step 4 — Check Your Work
As with any math equation, the last stage of balancing chemical equations is checking your work. Go over your calculations again and make sure that everything adds up.
And you’re done! Your equation is balanced, in four easy steps.
Knowing how to balance a chemical equation is a big part of chemistry, and it’s not as complicated as you might think. Remember, you’re never changing the subscripts that identify the number of atoms of each element in the formula. Coefficients added before each component in the equation are the tools you need to make sure that the equation meets the requirements of the Law of Conservation of Mass.
Everything comes back to the Law of Conservation of Mass, but that’s not the only reason you need to make sure your equations are balanced. If you’re planning on performing a chemistry experiment, balancing your formula gives you a basic idea of how much of each element you’ll need to create a balanced reaction. If you’re building water molecules with hydrogen and oxygen, for instance, your equation looks something like this:
H₂ + O₂ → H₂O
Now if you remember what we just talked about, you can see that this formula is unbalanced. You start with two oxygen and two hydrogens and end up with two hydrogens and one oxygen.
A balanced version of this equation looks like this:
2 H₂ + O₂ → 2 H₂O
This tells us that we need twice as much hydrogen, four atoms total, to create a balanced reaction to form two molecules of water. Can you follow the steps we took to balance that equation?
Just remember these four steps, and you’ll be a balancing expert in no time.