Starter

1. 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 Starter

2. Objectives • To understand how to balance symbol equations.

3. 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.

4. Balancing equations • 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

5. 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

6. Symbols Mg + O2 2 2  Mg + O2 MgO

7. You try – balance these equations • C + O2 CO2 • H2 + O2 H2O • N2 + H2 NH3 • CH4 + O2 CO2 + H2O

8. (s) (l) (g) (aq) E.g. H2 O2 CO2 H2O C State Symbols

9. 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) http://www.youtube.com/watch?v=8ypUVpwgcAA