Balancing Chemical Equations 21 st March 2012

Learning Objectives Recall the symbols for certain elements (Level 4) Describe the importance of balancing equations with reference to numbers (Level 5) Demonstrate how to calculate balanced chemical equations (Level 6)

What did we do last lesson? Can anyone remember what we did last lesson?

Starter Complete the worksheet

What is my symbol? Carbon C Nitrogen N Hydrogen H Oxygen O Sulfur S Boron B Helium He Calcium Ca Lead Pb Zinc Zn Answers

Can you….? Recall the symbols for certain elements (Level 4) YesNo Almost

Answers How do we write the symbols for these things? Water H 2 O Carbon Dioxide CO 2 Oxygen O 2 What do you notice about all these things?

Small numbers The small numbers we sometimes see are called subscripts. O 2 This subscript number means there are two oxygen atoms O

Big numbers The big numbers we sometimes see are called coefficients 2O 2 This coefficient number means there are two lots of the oxygen molecules O

Balancing equations When we talk about chemical reactions we always refer to the reactants and the products. When we write these chemical reactions we can sometimes use the formula instead of the word. Oxygen = O

Balancing Equations BUT, we must make sure that what goes into a chemical reaction also comes out WE MUST BALANCE THE EQUATION Lets have a go…

Role play I need… 4 Hydrogen's 1 Carbon 2 oxygen Methane + Oxygen Carbon dioxide + Water CH 4 + O 2 CO 2 + H 2 O

Balancing equations Methane + Oxygen Carbon Dioxide + Water What do you notice about this balanced equation? CH 4 + 2O 2 CO 2 2H 2 O CC H H H H O O O HH H H H H H H HH H H HH H H HH H H H H H H H H H H H H H H H H H H H O H H H H H O H H H H H H O H H H H H H H O H H H H

Can you….? Describe the importance of balancing equations with reference to numbers (Level 5) YesNoAlmost

Balancing equations You are now going to use the molly mod kits to try and balance these equations: 1. H 2 + O 2 H 2 O 2. Mg + O 2 MgO

Balancing equations Time for you to have a go… Hydrogen + Oxygen Water H 2 + O 2 H 2 O ??????? HHO Remember we need to balance it! What do you notice??

Balancing equations Time for you to have a go… Hydrogen + Oxygen Water H 2 + O 2 H 2 O HHO Remember we need to balance it! Why is this wrong?? Because we haven't used both of the oxygen molecules O H

Balancing equations Time for you to have a go… Hydrogen + Oxygen Water H 2 + O 2 2H 2 O HHO Remember we need to balance it, BOTH SIDES Is this correct?? O H OOO O

Balancing equations Time for you to have a go… Hydrogen + Oxygen Water 2H 2 + O 2 2H 2 O HHO Remember we need to balance it, BOTH SIDES Is this correct?? YES, There are now 4 hydrogen atoms and two oxygen atoms on the left AND the same amount on the right O H OOO O

Just count up the atoms on each side Then start balancing: Mg + O 2  MgO Mg O The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages And adjust totals Mg + O 2  MgO Mg O

Mg + O 2  MgO Mg O But the numbers still aren ’ t equal, so add another “ BIG ” number 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!! 2

Can you….? Create balanced chemical equations (Level 6) YesNoAlmost

Plenary I want you to write..… One learning objective you have achieved today One thing you have learnt today And if it was too easy, about right, or too hard