Balancing chemical equations is essential in chemistry because it ensures that the law of conservation of mass is upheld. This law states that the number of atoms for each element must be the same on both sides of the equation. Unbalanced equations do not correctly represent chemical reactions and can lead to errors in calculations and experiments.
In this guide, you will find 50 fully balanced chemical equations, categorized by different types of reactions, along with explanations and tips.
🔹 Rules for Balancing Chemical Equations
Before we dive into examples, here are some general steps to balance chemical equations:
✅ Step 1: Identify reactants and products.
✅ Step 2: Write down the unbalanced equation.
✅ Step 3: Count atoms for each element on both sides.
✅ Step 4: Use coefficients to balance the number of atoms.
✅ Step 5: Double-check to ensure all elements are balanced.
📌 1. Combination (Synthesis) Reactions
Combination reactions occur when two or more reactants combine to form a single product.
| Unbalanced Equation | Balanced Equation | Explanation |
|---|---|---|
| H₂ + O₂ → H₂O | 2H₂ + O₂ → 2H₂O | Oxygen is diatomic (O₂), so we need 2 H₂ molecules. |
| N₂ + H₂ → NH₃ | N₂ + 3H₂ → 2NH₃ | Nitrogen and hydrogen are both diatomic molecules. |
| C + O₂ → CO₂ | C + O₂ → CO₂ | Carbon and oxygen form carbon dioxide. |
| Fe + O₂ → Fe₂O₃ | 4Fe + 3O₂ → 2Fe₂O₃ | Iron reacts with oxygen to form iron(III) oxide (rust). |
| Mg + O₂ → MgO | 2Mg + O₂ → 2MgO | Magnesium burns in oxygen to form magnesium oxide. |
📌 2. Decomposition Reactions
Decomposition reactions occur when a single compound breaks into two or more products.
| Unbalanced Equation | Balanced Equation | Explanation |
|---|---|---|
| H₂O₂ → H₂O + O₂ | 2H₂O₂ → 2H₂O + O₂ | Hydrogen peroxide decomposes into water and oxygen. |
| KClO₃ → KCl + O₂ | 2KClO₃ → 2KCl + 3O₂ | Potassium chlorate breaks into potassium chloride and oxygen gas. |
| CaCO₃ → CaO + CO₂ | CaCO₃ → CaO + CO₂ | Calcium carbonate decomposes into calcium oxide and carbon dioxide. |
| NH₄NO₃ → N₂ + H₂O + O₂ | NH₄NO₃ → N₂ + 2H₂O + 1/2O₂ | Ammonium nitrate decomposes into nitrogen, water, and oxygen. |
| NaHCO₃ → Na₂CO₃ + CO₂ + H₂O | 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O | Baking soda decomposes when heated. |
📌 3. Single Replacement Reactions
In single replacement reactions, one element replaces another in a compound.
| Unbalanced Equation | Balanced Equation | Explanation |
|---|---|---|
| Zn + HCl → ZnCl₂ + H₂ | Zn + 2HCl → ZnCl₂ + H₂ | Zinc replaces hydrogen in hydrochloric acid. |
| Fe + CuSO₄ → FeSO₄ + Cu | Fe + CuSO₄ → FeSO₄ + Cu | Iron replaces copper in copper(II) sulfate. |
| Cl₂ + NaBr → NaCl + Br₂ | Cl₂ + 2NaBr → 2NaCl + Br₂ | Chlorine replaces bromine in sodium bromide. |
| Mg + H₂SO₄ → MgSO₄ + H₂ | Mg + H₂SO₄ → MgSO₄ + H₂ | Magnesium replaces hydrogen in sulfuric acid. |
| Al + Fe₂O₃ → Al₂O₃ + Fe | 2Al + Fe₂O₃ → Al₂O₃ + 2Fe | Aluminum replaces iron in iron(III) oxide. |
📌 4. Double Replacement Reactions
In double replacement reactions, two compounds exchange ions to form new compounds.
| Unbalanced Equation | Balanced Equation | Explanation |
|---|---|---|
| NaCl + AgNO₃ → NaNO₃ + AgCl | NaCl + AgNO₃ → NaNO₃ + AgCl | Silver chloride precipitates out. |
| BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl | BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl | Barium sulfate forms as a precipitate. |
| Pb(NO₃)₂ + KI → PbI₂ + KNO₃ | Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃ | Lead iodide forms as a solid. |
| HCl + NaOH → NaCl + H₂O | HCl + NaOH → NaCl + H₂O | A neutralization reaction occurs. |
| CaCl₂ + Na₂CO₃ → CaCO₃ + NaCl | CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl | Calcium carbonate forms. |
📌 5. Combustion Reactions
Combustion reactions involve a fuel (hydrocarbon) reacting with oxygen, producing CO₂ and H₂O.
| Unbalanced Equation | Balanced Equation | Explanation |
|---|---|---|
| CH₄ + O₂ → CO₂ + H₂O | CH₄ + 2O₂ → CO₂ + 2H₂O | Methane burns completely in oxygen. |
| C₂H₆ + O₂ → CO₂ + H₂O | 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O | Ethane undergoes complete combustion. |
| C₃H₈ + O₂ → CO₂ + H₂O | C₃H₈ + 5O₂ → 3CO₂ + 4H₂O | Propane combustion reaction. |
| C₄H₁₀ + O₂ → CO₂ + H₂O | 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O | Butane combustion reaction. |
| C₆H₁₂O₆ + O₂ → CO₂ + H₂O | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O | Glucose undergoes cellular respiration. |
💡 Key Takeaways
- Balancing equations ensures mass conservation (atoms on both sides are equal).
- Coefficients (big numbers in front) adjust the number of molecules.
- Some reactions are straightforward, while others require trial and error.
- Common reactions include combustion, decomposition, and acid-base neutralization.