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

General Rules for balancing chemical equations – Rule 4

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 4: Balancing chemical equations using the even technique.

If you have an even number of a certain element on one side of the equation and an odd number of the same element on the other side of the equation, multiply both sides of the equation through by the coefficient of 2. This will give an even number on both sides and make the equation easier to balance.

Example:

Balance the equation

CH₃OH + O₂ → H₂O + CO₂

Solution:

Step 1: Using the CHO technique, we start with carbon, one on each side, so carbon is balanced. There are four H on the left and two on the right, so we place the coefficient of 2 in front of the H₂O on the right

CH₃OH + O₂ → 2H₂O + CO₂

Step 2: When we try to balance the oxygen, we find three on the left and four on the right. We multiply both sides of the equation through by two.

2CH₃OH + 2O₂ → 4H₂O + 2CO₂

Step 3: The C and H are still balanced, and now there are six O on the left and eight on the right. Change the coefficient in front of the O₂ to 3 to give eight O on the left.

2CH₃OH + 3O₂ → 4H₂O + 2CO₂

Step 4: Check that all the atoms balance and make sure that all coefficients are in the lowest-possible ratio.

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