How do you balance a chemical equation, also called a reaction equation?

A chemical transformation is a transformation during which substances disappear, called the reactants, while other substances form, called the products.

A chemical reaction is the model associated with a chemical transformation.

Reactants are the substances that disappear during a chemical reaction.

Products are the substances that appear during a chemical reaction.

A reaction equation is the symbolic notation that uses the symbols and formulas of the chemical species involved in the chemical reaction.

Example: Complete carbon combustion 🔥

Example: Complete methane combustion 🔥

Balancing a chemical equation means determining the numbers, or coefficients, to place in front of the chemical species so that the atoms present in the reactants are identical in nature and number to the atoms present in the products.

• Method:
• – First, balance the atoms present in only one reactant and one product.
• – For alkane combustions C_nH_2n+2, balance the atoms in the following order: C, H, and O.
• – When one of the numbers is not an integer, multiply all the numbers by 2.

We are going to balance the following chemical equation:

CH₄ + O₂ → CO₂ + H₂O

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We start by checking the carbon atom C, which is present in only one reactant and one product:

CH₄ + O₂ → CO₂ + H₂O 1C₁H₄ + 1O₂ → 1C₁O₂ + 1H₂O₁
 Click to add 1 coefficients 

The carbon atom C is balanced: 1 carbon atom in the reactants and 1 carbon atom in the products.

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Next, we check the hydrogen atom H, which is also present in only one reactant and one product.

CH₄ + O₂ → CO₂ + H₂O 1C₁H₄ + 1O₂ → 1C₁O₂ + 1H₂O₁
 Click to add 1 coefficients 

The hydrogen atom H is not balanced: 4 hydrogen atoms in the reactants and 2 hydrogen atoms in the products.
Hydrogen atoms are missing from the products.
We modify the number in front of the chemical species in the products that contains hydrogen atoms. This is the water molecule H₂O.

CH₄ + O₂ → CO₂ + 2H₂O 1C₁H₄ + 1O₂ → 1C₁O₂ + 2H₂O₁
 Click to add 1 coefficients 

The hydrogen atom is now balanced: 4 hydrogen atoms in the reactants and 4 hydrogen atoms in the products.

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We finish with the oxygen atom O, which is present in only one reactant and in the two products.

CH₄ + O₂ → CO₂ + 2H₂O 1C₁H₄ + 1O₂ → 1C₁O₂ + 2H₂O₁
 Click to add 1 coefficients 

The oxygen atom O is not balanced: 2 oxygen atoms in the reactants and 4 oxygen atoms in the products.
Oxygen atoms are missing from the reactants.
We modify the number in front of the chemical species in the reactants that contains oxygen atoms. This is the dioxygen molecule O₂.

CH₄ + 2O₂ → CO₂ + 2H₂O 1C₁H₄ + 2O₂ → 1C₁O₂ + 2H₂O₁
 Click to add 1 coefficients 

The oxygen atom O is now balanced: 4 oxygen atoms in the reactants and 4 oxygen atoms in the products.

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The balanced chemical equation for methane combustion is:

CH₄ + 2O₂ → CO₂ + 2H₂O 1C₁H₄ + 2O₂ → 1C₁O₂ + 2H₂O₁
 Click to add 1 coefficients