Balancing equations

Science

Definition

Balancing chemical equations is the process of adjusting coefficients so that the same number of each type of atom appears on both sides of the equation, satisfying the law of conservation of mass. Only coefficients (not subscripts) may be changed.

How It Works

  1. Write the unbalanced equation with correct chemical formulas for all reactants and products.
  2. List the number of atoms of each element on both sides of the equation.
  3. Start by balancing elements that appear in only one reactant and one product.
  4. Balance hydrogen and oxygen atoms last (they often appear in multiple compounds).
  5. Adjust coefficients to equalize atom counts on both sides; use fractions if needed, then multiply through to get whole numbers.
  6. Verify that all atoms are balanced and coefficients are in the lowest whole-number ratio.

Examples

  • Combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O
  • Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
  • Rusting of iron: 4Fe + 3O₂ → 2Fe₂O₃
Key Fact

Atoms in = Atoms out; change coefficients only, never subscripts.

Related Terms

Conservation of mass Stoichiometry Molar ratios Reaction types

Study This Concept

Practice balancing equations with free review games in these units:

Chemistry Unit 4: Chemical Reactions and Equations