1. How to write balanced equations: step by step guide
Chemical equations
How to write balanced equations: step by step guide

2. magnesium + oxygen → magnesium oxide
What is an equation?
A chemical equation describes how substances react with each other.
The chemicals on the left are the reactants. These react to form the products which are on the right.
This equation describes how magnesium burns in oxygen.
magnesium + oxygen → magnesium oxide
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3. magnesium + oxygen → magnesium oxide
What is an equation?
Word equations don't show the atoms in the chemicals.
magnesium + oxygen → magnesium oxide
Using symbols helps to show the detail about what is happening in the reaction.
Mg O → MgO
This equation is not balanced. There are more oxygen atoms on the left than on the right. This suggests that an oxygen atom just disappears. This can't happen. We need to balance the equation.

4. magnesium + oxygen → magnesium oxide
Balancing atoms
magnesium + oxygen → magnesium oxide
Mg O → MgO
First note the number of atoms of each element on the right and left of the equation. Mg
Balanced O
Unbalanced
Which elements are balanced on each side?

5. Balancing atoms
magnesium + oxygen → magnesium oxide
Mg O → MgO Mg
Balanced O
Unbalanced
How can we balance the oxygen atoms?

6. magnesium + oxygen → magnesium oxide
Balancing atoms
magnesium + oxygen → magnesium oxide
Mg O → MgO 2
The oxygen atoms are balanced but now the magnesium atoms are not. Mg
Unbalanced O
Balanced
Top Tip!
You can't just write MgO2
That would change the formula for magnesium oxide and you can't do that.
Numbers to balance equations always go in front of the formula.
How can we balance the oxygen atoms?

7. magnesium + oxygen → magnesium oxide
Balancing atoms
magnesium + oxygen → magnesium oxide
Mg O → MgO 2 2
The oxygen atoms are balanced but now the magnesium atoms are not.
The magnesium and oxygen atoms are equal on both sides of the equation. Mg O
Balanced Mg O
Unbalanced
Balanced
How can we balance the magnesium atoms?
This is the balanced equation.

8. Balancing equations: step-by-step
magnesium + oxygen → magnesium oxide
Write the symbol equation.
Mg O2 → MgO
Count the atoms of each element on the left and right of the equation. Mg O
Choose one element to balance.
Mg O2 → MgO 2
Count the atoms again.
Do any others need balancing? Mg O
Mg O2 → MgO
Balance the next element and check again. You may need to do this a few times to get it all balanced. 2 2 Mg O
Don't forget! You can’t change the formula of a chemical.
Numbers to balance equations always go in front of a formula.