Balanced Equations and State Symbols

Chemical equations are the language of chemistry. A balanced equation tells you exactly what reacts, what is produced, and in what proportions. Getting comfortable with writing and balancing equations is essential for every area of A-Level Chemistry.

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Why Equations Must Be Balanced

Atoms cannot be created or destroyed in a chemical reaction — this is the law of conservation of mass. A balanced equation has the same number of each type of atom on both sides of the arrow. An unbalanced equation violates this fundamental law.

For example, the unbalanced equation for the combustion of methane is:

CH₄ + O₂ → CO₂ + H₂O (unbalanced)

Counting atoms: Left side has 1C, 4H, 2O. Right side has 1C, 2H, 3O. This is not balanced.

The balanced equation is:

CH₄ + 2O₂ → CO₂ + 2H₂O

Now: Left = 1C, 4H, 4O. Right = 1C, 4H, 4O. Balanced.

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Systematic Balancing Method

For most equations, follow this approach: