Chemical equations are used to describe chemical reactions. They show what substances react and what substances are produced.

There are two main types of equations:

• Word equations
• Symbol equations (which must be balanced)

Word equations

Word equations describe a reaction using names of substances.

Example:

Magnesium + oxygen → magnesium oxide

This shows that magnesium reacts with oxygen to make magnesium oxide.

General format:

Reactants → Products

• Reactants are the substances that react (left-hand side)
• Products are the new substances formed (right-hand side)

Symbol equations

Symbol equations use chemical formulae instead of names.

Using the example above:

Mg + O₂ → MgO

This gives more detail, but it also needs to be balanced so that the number of atoms is the same on both sides.

Balancing equations

In a chemical reaction, atoms are not created or destroyed. The total number of atoms of each element must be equa lon both sides of the equation.

Unbalanced:

Mg + O₂ → MgO

• Left: 1 Mg, 2 O
• Right: 1 Mg, 1 O

This is not balanced.

Balanced:

2Mg + O₂ → 2MgO

• Left: 2 Mg, 2 O
• Right: 2 Mg, 2 O ✅

We add big numbers in front of the formulae to balance. Never change small numbers in a formula (like subscripts), because that changes the substance.

Step-by-step balancing method

1. Write the correct formulae for all reactants and products
2. Count the number of atoms of each element on both sides
3. Use big numbers (coefficients) to make the number of atoms equal
4. Double-check all elements are balanced

Example: Iron + oxygen → iron oxide

Word equation: Iron + oxygen → iron oxide

Unbalanced symbol equation: Fe + O₂ → Fe₂O₃

Count atoms:

• Left: Fe = 1, O = 2
• Right: Fe = 2, O = 3

Balanced version:

4Fe + 3O₂ → 2Fe₂O₃