Skip to main content

Balancing Chemical Equations

🔄 Quick Recap​

We've learned that chemical equations use symbols and formulas to represent reactions. But there's one critical rule: the number of atoms must be the same on both sides of the equation.

📚 The Law of Conservation of Mass​

A French chemist named Antoine Lavoisier discovered that matter can neither be created nor destroyed during a chemical reaction. This is called the Law of Conservation of Mass.

In simpler terms: The total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.

This means that in a chemical equation, the number of atoms of each element must be equal on both sides of the arrow. That's why we need to balance chemical equations.

🖼️ Balancing Chemical Equations Step-by-Step​

Balancing an equation means adding coefficients (numbers) in front of chemical formulas to make the number of atoms equal on both sides. We never change the subscripts in the formula.

Let's learn the process with a detailed example:

Balancing Equations Step-by-Step

📚 The Hit-and-Trial Method​

The most common way to balance equations is the "hit-and-trial" method, where we systematically adjust coefficients until the equation is balanced.

Step-by-Step Approach:​

  1. Write the correct formula for each reactant and product
  2. Count the atoms of each element on both sides
  3. Begin with the most complex compound or the element with the most atoms
  4. Balance one element at a time, usually starting with metals, then non-metals
  5. Double-check by counting atoms of each element on both sides again

🧮 Mathematical Corner: More Examples​

Example 1: Hydrogen + Oxygen → Water​

Step 1: Write the unbalanced equation

H₂ + O₂ → H₂O

Step 2: Count atoms

  • Left side: 2 H atoms, 2 O atoms
  • Right side: 2 H atoms, 1 O atom
  • Oxygen is not balanced!

Step 3: Try to balance oxygen by adding a coefficient to H₂O

H₂ + O₂ → 2H₂O

Now count again:

  • Left side: 2 H atoms, 2 O atoms
  • Right side: 4 H atoms, 2 O atoms
  • Oxygen is balanced, but hydrogen is not!

Step 4: Balance hydrogen by adding a coefficient to H₂

2H₂ + O₂ → 2H₂O

Final count:

  • Left side: 4 H atoms, 2 O atoms
  • Right side: 4 H atoms, 2 O atoms
  • All atoms are balanced! ✓

Example 2: Aluminum + Oxygen → Aluminum Oxide​

Step 1: Write the unbalanced equation

Al + O₂ → Al₂O₃

Step 2: Count atoms

  • Left side: 1 Al atom, 2 O atoms
  • Right side: 2 Al atoms, 3 O atoms
  • Neither element is balanced!

Step 3: Let's balance aluminum first

2Al + O₂ → Al₂O₃

Aluminum is now balanced, but oxygen is not.

Step 4: Balance oxygen

4Al + 3O₂ → 2Al₂O₃

Final count:

  • Left side: 4 Al atoms, 6 O atoms
  • Right side: 4 Al atoms, 6 O atoms
  • All atoms are balanced! ✓

✅ Solved Examples​

Example 3: Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate + Water​

Step 1: Write the unbalanced equation with correct formulas

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Step 2: Count atoms on each side

ElementLeft Side (Reactants)Right Side (Products)
Ca11
O2 (from OH) + 2 (from CO₂) = 43 (from CaCO₃) + 1 (from H₂O) = 4
H22
C11

This equation is already balanced! All atoms are equal on both sides.

Example 4: Zinc + Hydrochloric Acid → Zinc Chloride + Hydrogen​

Step 1: Write the unbalanced equation

Zn + HCl → ZnCl₂ + H₂

Step 2: Count atoms

  • Left side: 1 Zn atom, 1 H atom, 1 Cl atom
  • Right side: 1 Zn atom, 2 H atoms, 2 Cl atoms
  • Cl and H are not balanced!

Step 3: Balance Cl by adding a coefficient to HCl

Zn + 2HCl → ZnCl₂ + H₂

Final count:

  • Left side: 1 Zn atom, 2 H atoms, 2 Cl atoms
  • Right side: 1 Zn atom, 2 H atoms, 2 Cl atoms
  • All atoms are balanced! ✓

🧪 Activity Time!​

Practice Balancing These Equations:​

  1. Fe + O₂ → Fe₂O₃
  2. KClO₃ → KCl + O₂
  3. CH₄ + O₂ → CO₂ + H₂O
  4. NaOH + H₂SO₄ → Na₂SO₄ + H₂O

(Work through these step by step, checking your atoms on both sides!)

⚠️ Common Misconceptions​

  1. Misconception: You can change the subscripts in a formula to balance an equation. Truth: Never change subscripts! This would change the identity of the substances. Only use coefficients (numbers in front of formulas).

  2. Misconception: There's only one way to balance an equation. Truth: You can balance equations by starting with different elements, but the final balanced equation will have the same ratio of coefficients.

  3. Misconception: Fractional coefficients are incorrect. Truth: Fractional coefficients can be used in intermediate steps, but we usually convert to whole numbers in the final equation.

🧠 Memory Tricks​

Remember the phrase "NEVER SUB, ONLY COEF" to remind yourself:

  • NEVER change SUBscripts
  • ONLY change COEFficients

💡 Key Points to Remember​

  • The Law of Conservation of Mass requires that atoms are neither created nor destroyed in a chemical reaction
  • Chemical equations must be balanced to satisfy this law
  • We balance equations by adding coefficients in front of formulas
  • Never change the subscripts in chemical formulas
  • Start balancing with the most complex formula or the element appearing in the fewest compounds
  • The final check: count each type of atom on both sides to ensure they're equal

🤔 Think About It!​

  1. Why is it important to balance chemical equations?
  2. What would happen if we tried to balance equations by changing the subscripts instead of using coefficients?
  3. Can you think of a real-life analogy to help explain the Law of Conservation of Mass?

🔜 What Next?​

Now that we can write and balance chemical equations, we're ready to explore the different types of chemical reactions. Starting with combination reactions, we'll categorize reactions based on how atoms rearrange themselves.