How to Balance Chemical Reactions

Knowing how to balance a chemical reaction is a fundamental part of chemistry. The first law of thermodynamics says that energy cannot be created or destroyed. Yet when you first look at some chemical reactions it appears as though it can. This is where balancing comes in. The best way to balance chemical reactions is to think of them as mathematical equations. On the left side you have the reactants, on the right side you have the products, and the sides should equal each other. The main difference is that in the middle you have an arrow instead of an equals sign.

Things You'll Need

• Pencil
• Paper
• Calculator

Instructions

Balancing A Chemical Reaction

1. Take your pencil and write the chemical reaction on your paper. Let's use the example of ethane + oxygen --> carbon dioxide + steam, or C2H6 + O2 --> CO2 + H2O.

2. Look at the equation and notice what does not match up on both sides. In this case the carbons, hydrogens and oxygens don't equal out.

3. Pick one of the atoms that don't equal and balance it by placing a multiplier in front of the compound. Let's start with the carbons. Two carbon atoms are on the left, and one carbon atom on the right. To balance the carbons, we will place a multiplier in front of the carbon dioxide on the right. Now the reaction looks like:
   C2H6 + O2 --> 2CO2 + H2O

4. Pick another atom that needs balancing and place a multiplier in front of the compound. Let's work on the hydrogen atoms next. Six atoms of hydrogen are on the left, and now two atoms are on the right. To balance the hydrogen atoms, we will place a multiplier in front of the water molecule on the right. Now the reaction looks like: C2H6 + O2 --> 2CO2 + 3H2O

5. Pick another atom that needs balancing and place a multiplier in front of the compound. In our case oxygen is the only one left. Two atoms of oxygen are on the left and seven atoms of oxygen are on the right. To balance the oxygen atoms, we will place a multiplier in front of the oxygen molecule on the left. Now the reaction looks like:
   C2H6 + 3.5O2 --> 2CO2 + 3H2O

6. Continue picking atoms and adding multipliers until the reaction is balanced.

7. Eliminate all fractions from your balanced reaction by picking a number to multiply the whole reaction by. In our example, multiplying the whole reaction by 2 will turn our 3.5 multiplier into a whole number. Now our final balanced reaction is:
   2C2H6 + 7O2 --> 4CO2 + 6H2O

Tips & Warnings

• The multipliers you use must be applied to the whole molecule, not just a part of it. Balance elements like oxygen (O2) last.

References

• Sky-Web