Balancing a Simple Chemical Equation: Step-by-Step Guide

Balancing a simple chemical equation is the process of ensuring that the number of atoms for each element involved in a chemical reaction is the same on both the reactant (left) and product (right) sides of the equation. This is done by adjusting the coefficients (the numbers placed before chemical formulas) without altering the subscripts (the small numbers within chemical formulas that indicate the number of atoms in a molecule).

Purpose:

Conservation of Mass: According to the Law of Conservation of Mass, matter cannot be created or destroyed in a chemical reaction. Balancing ensures that the mass of the reactants equals the mass of the products.
Accurate Representation: A balanced equation accurately represents the quantities of reactants and products involved in the reaction, which is essential for calculations in stoichiometry.

Let’s balance the chemical equation for the reaction between hydrogen and oxygen to form water:

Step 1: Write the Unbalanced Equation

Start by writing the chemical formulas of the reactants and products:

H2+O2→H2O

Step 2: Count the Number of Atoms of Each Element

Hydrogen (H)

Reactants: 2 atoms ()

Products: 2 atoms ()

Oxygen (O)

Reactants: 2 atoms ()
Products: 1 atom ()

Step 3: Identify Which Element to Balance First

It’s often easiest to start with elements that appear in only one reactant and one product. Here, hydrogen is already balanced, so we’ll balance oxygen next.

Step 4: Balance Oxygen Atoms

Reactants have 2 oxygen atoms (), while products have 1 oxygen atom per molecule of water.
To balance, we need 2 water molecules to have 2 oxygen atoms on the product side.

H2+O2→2H2O

Step 5: Recount the Atoms After Adjusting

Hydrogen (H)
- Reactants: 2 atoms ()
- Products: 4 atoms ()
- Oxygen (O)
  - Reactants: 2 atoms ()
  - Products: 2 atoms ()

Step 6: Balance Hydrogen Atoms

Now, hydrogen is unbalanced. There are 2 atoms on the reactant side and 4 on the product side.

To balance hydrogen, place a coefficient of 2 before $H2\text{H}_2$ :

Step 7: Final Atom Count

Hydrogen (H)
Reactants: 4 atoms ( $2 \times H_{2}$ )
Products: 4 atoms ( $2 \times H_{2} O$ )
Products: 4 atoms ( $2 \times H_{2} O$ )

Step 8: Verify the Balanced Equation

All elements have the same number of atoms on both sides. The balanced equation is:

2H2 + O2 → 2H2O

Key Points to Remember When Balancing Equations:

Only Change Coefficients: Never change the subscripts in the chemical formulas.
Start with Complex Molecules: Balance elements that appear in only one reactant and one product first.
Balance Polyatomic Ions as Units: If a polyatomic ion doesn’t change during the reaction, balance it as a whole.
Leave Hydrogen and Oxygen for Last: These elements often appear in multiple reactants and products.
Ensure the Simplest Whole Number Ratios: After balancing, coefficients should be in the lowest possible whole numbers.