Balancing chemical equations

Atoms can neither be destroyed nor created during a simple chemical reaction. Therefore, in a chemical reaction

The sum of atoms before reaction = the sum of atoms after reaction

The following figure gives some hints on how to balance chemical equations. Scroll down the page for more examples and solutions.

General Rules for balancing chemical equations

Balancing chemical equations may require some trial and error. There are some general rules that could be helpful, but they may not work all the time.

• Rule 1: Balancing chemical equations using the one’s and two’s technique
• Rule 2: Balancing chemical equations using the two’s and three’s technique
• Rule 3: Balancing chemical equations using the CHO technique
• Rule 4: Balancing chemical equations using the even technique
• Rule 5: Balancing chemical equations containing polyatomic ions

In this page, we will look at some examples of applying

Rule 2: Balancing chemical equations using the two’s and three’s technique.

Example:

Balance the equation

Fe + O₂ → Fe₂O₃

Solution:

Step 1: On the left side of the equation there are 2 oxygen atoms and on the right side of the equation there are 3 oxygen atoms. To balance the oxygen atoms, multiply Fe₂O₃ by the coefficient of 2 and the O₂ by the coefficient of 3

Fe + 3O₂ → 2Fe₂O₃

Step 2: Balance the Fe by placing the coefficient of 4 in front of Fe

4Fe + 3O₂ → 2Fe₂O₃

Step 3: Check that all the atoms balance and make sure that all coefficients are in the lowest-possible ratio.

Examples of using the two's and three's method to balance chemical equations

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