1. Starter What are the formulas for the following compounds:
What are the symbols for the following elements:
Sodium
Oxygen
Chlorine
Iron
Copper
What are the formulas for the following compounds:
Water
Potassium hydroxide
Magnesium oxide
Potassium iodide
Caesium oxide Na O Cl Fe Cu
1. H2O
2. KOH
3. MgO
4. KI
5. Cs2O

2. Key facts In chemical reactions new substances are made.
A reaction can be summarised in a word equation or a symbol equation.
The total mass of reactants is the same as the total mass of products in a reaction
A symbol equation must be balanced as no atoms are created or destroyed.
The conservation of mass in a chemical reaction is an essential prerequisite to understanding why we need to balance equations.

3. Balancing equations C2O X CO4 X C2O2 X 2CO2
You can never change a formula when balancing an equation. You can only put a number in front of a formula.
Lets consider how to show 2 molecules of CO2:
C2O X
CO4 X
C2O2 X
2CO2
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4. Symbol equations
No atoms are created or destroyed in a chemical reaction.
There should be the same number of atoms of each type of element each side of the equation.
Magnesium + Oxygen Magnesium oxide
Write the balanced symbol equation below explaining how you balance it at the same time (2Mg +O2  2MgO)

5. 2
Mg + O2  MgO 2 
Symbols Mg + O2

6. Balanced or unbalanced?

7. Al + 2 Cl2 AlCl3 Atom Type Left hand side Right hand side Balanced? Al Cl

8. 2Na + 2Cl2 2NaCl
Atom Type
Left hand side
Right hand side
Balanced?

9. You try – balance these equations
C O CO2
H O H2O
N H NH3
CH4 + O CO H2O
Already balanced
2H2 + O2  2H2O
2N2 + 3H2  2NH3
CH4 + 2O2  CO2 + 2H2O

10. State Symbols H2 O2 CO2 H2O C E.g. (s) (l) (g) (aq)
State that the temperature should be room (25oC).
H2(g)
O2(g)
CO2(g)
H2O(l)
C(s)

11. What is wrong with this equation?
Lithium was added to water in a school lab. Below is the symbol equation for the reaction – or is it?
Li(s)+ H2O(s)  LiO(aq) + H2(g)
This reaction would make lithium hydroxide.
Water is a liquid at room temperature.
Lithium oxide immediately reacts with water to make lithium hydroxide therefore this phase of lithium oxide is not possible.
Extension – get the students to complete the correct symbol equation for this reaction.