Balancing Chemical Equations

Master the law of conservation of mass by balancing atoms on both sides of the arrow

CAPS Grade 10 Physical Sciences
Did you know? The Law of Conservation of Mass was discovered by Antoine Lavoisier in 1789. He proved that matter cannot be created or destroyed in chemical reactions - this is why we must balance equations!

Balancing equations is like solving a puzzle where every atom must be accounted for on both sides of the arrow. This guide will take you through the process step by step, with plenty of practice opportunities.

1. The Golden Rule: Never Change Subscripts

Important Warning

Changing subscripts creates a completely different substance. You can ONLY add coefficients in front of chemical formulas.

2H₂O

Correct: Use Coefficients

2H₂O means 2 molecules of water

H
H
O
+
H
H
O

Total: 4 H atoms, 2 O atoms

H₂O₂

Wrong: Changing Subscripts

H₂O₂ means hydrogen peroxide (different chemical!)

H
H
O
O

Total: 2 H atoms, 2 O atoms

Quick Check

What does 3NH₃ represent?

2. Step-by-Step Balancing Tutorial

1 Count the Atoms - List all elements and count them on both sides
2 Balance Metals First - Start with elements that appear in only one compound
3 Save H and O for Last - They often appear in multiple compounds
4 Check Your Work - Recount all atoms to verify balance

Example: Balancing CH₄ + O₂ → CO₂ + H₂O

Click on any step above to see how it applies to this equation

Carbon (C) Left: 1 | Right: 1
Hydrogen (H) Left: 4 | Right: 2
Oxygen (O) Left: 2 | Right: 3

Visual Equation Builder

Use the + and - buttons to balance: H₂ + O₂ → H₂O

1
H₂ +
1
O₂ →
1
H₂O

Reactants

Products

H: 2 → 2
O: 2 → 1

3. Conservation of Atoms vs Molecules

Remember: Atoms are always conserved (same number on both sides). Molecules can change count!

2H₂ + O₂

Reactants

Molecules: 3 total

Atoms: 4 H, 2 O

2H₂O

Products

Molecules: 2 total

Atoms: 4 H, 2 O

Quick Check

In a balanced equation, what is ALWAYS conserved?

Practice Zone

Choose your difficulty level
H₂ + Cl₂ → 2HCl

4. Polyatomic Ions - The Shortcut

Balance Polyatomic Ions as a Unit!

If SO₄²⁻ appears on both sides, treat it as one "chunk" - balance the whole ion together.

NaOH + H₂SO₄ → Na₂SO₄ + H₂O
SO₄ (sulfate) acts as 1 unit

Try it yourself:

Balance: _NaOH + _H₂SO₄ → _Na₂SO₄ + _H₂O

Hint: Balance SO₄ first (it's already balanced!)

Quick Fire Challenge

Select the correct coefficients for: H₂ + O₂ → H₂O

Interactive Quizzes

Test your balancing skills with these complete quizzes

Beginner Quiz

5 questions - Simple equations

5 questions Easy

Intermediate Quiz

8 questions - With polyatomic ions

8 questions Medium

Advanced Quiz

10 questions - Complex equations

10 questions Hard

Key Terms

Coefficient Subscript Conservation of Mass Reactant Product Polyatomic Ion Balance by Inspection Chemical Equation Atom Molecule

Key Takeaways

Writing Chemical Equations Types of Reactions