Balancing Chemical Equations
Write and balance symbol equations using the law of conservation of mass.
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Atoms are never created or destroyed in a chemical reaction.
In this lesson you will:
- Write word equations and symbol equations.
- Balance equations by adjusting coefficients.
- Identify reaction types.
From Words to Symbols
Hydrogen + oxygen → water becomes 2H₂ + O₂ → 2H₂O. Subscripts show atoms in a molecule; coefficients show how many molecules react.
Balancing Steps
- Write the unbalanced equation.
- Count each type of atom on both sides.
- Add coefficients in front of formulas — never change subscripts.
- Recount and repeat until every element balances.
- Check charges if ions are involved.
Reaction Types
- Combination — two substances join.
- Decomposition — one substance breaks down.
- Combustion — reaction with oxygen releasing heat and light.
- Neutralisation — acid plus base.
- Precipitation — an insoluble solid forms.
Balance it
Unbalanced: CH₄ + O₂ → CO₂ + H₂O.
Carbon and hydrogen balance need 1 CH₄ and 2 H₂O. Oxygen then needs 2 O₂.
Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O.
Warning Never change a formula to balance an equation. H₂O is water; changing it to H₂O₂ makes a different substance.
Practice
- Balance: H₂ + O₂ → H₂O.
- Balance: Fe + O₂ → Fe₂O₃.
- Classify the reaction: CaCO₃ → CaO + CO₂.
Recap
Balanced equations obey conservation of mass. Adjust coefficients only, and check every element.
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Course contents
Chemical Reactions and Equations
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