1. IC4.4.4 Chemical equations © Oxford University Press 2011 Chemical equations How to write balanced equations: step by step guide

2. IC4.4.4 Chemical equations © Oxford University Press 2011 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

3. IC4.4.4 Chemical equations © Oxford University Press 2011 What is an equation? 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. Using symbols helps to show the detail about what is happening in the reaction. Word equations don't show the atoms in the chemicals. magnesium + oxygen → magnesium oxide Mg + O 2 → MgO

4. IC4.4.4 Chemical equations © Oxford University Press 2011 Balancing atoms Which elements are balanced on each side? magnesium + oxygen → magnesium oxide Mg 1 1 Mg + O 2 → MgO O 2 1 Balanced Unbalanced First note the number of atoms of each element on the right and left of the equation.

5. IC4.4.4 Chemical equations © Oxford University Press 2011 magnesium + oxygen → magnesium oxide Balancing atoms Mg 1 1 O 2 1 Balanced Unbalanced How can we balance the oxygen atoms? Mg + O 2 → MgO

6. IC4.4.4 Chemical equations © Oxford University Press 2011 magnesium + oxygen → magnesium oxide Balancing atoms 2 Mg 1 2 O 2 2 Unbalanced Balanced Top Tip! You can't just write MgO 2 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? The oxygen atoms are balanced but now the magnesium atoms are not. Mg + O 2 → MgO

7. IC4.4.4 Chemical equations © Oxford University Press 2011 magnesium + oxygen → magnesium oxide Balancing atoms 2 How can we balance the magnesium atoms?This is the balanced equation. The magnesium and oxygen atoms are equal on both sides of the equation. Mg 1 2 O 2 2 Unbalanced Balanced Mg 2 2 O 2 2 Balanced The oxygen atoms are balanced but now the magnesium atoms are not. Mg + O 2 → MgO 2

8. IC4.4.4 Chemical equations © Oxford University Press 2011 magnesium + oxygen → magnesium oxide Mg + O 2 → MgO Balancing equations: step-by-step Mg 1 1 O 2 1 Mg + O 2 → MgO 2 Mg 1 2 O 2 2 Mg + O 2 → MgO 2 Mg 2 2 O 2 2 2 Don't forget! You can’t change the formula of a chemical. Numbers to balance equations always go in front of a formula. Write the symbol equation. Count the atoms of each element on the left and right of the equation. Choose one element to balance. Count the atoms again. Do any others need balancing? Balance the next element and check again. You may need to do this a few times to get it all balanced.