Balancing Chemical Equations21st 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?

StarterComplete the worksheet

Answers

What is my symbol?CarbonCNitrogenNHydrogenHOxygenOSulfurSBoronBHeliumHeCalciumCaLeadPbZincZn

Can you.?Recall the symbols for certain elements (Level 4)YesNoAlmostAlmostAlmost

AnswersHow do we write the symbols for these things?Water H2OCarbon Dioxide CO2Oxygen O2

What do you notice about all these things?

Small numbersThe small numbers we sometimes see are called subscripts.

O2

This subscript number means there are two oxygen atoms O O

Big numbersThe big numbers we sometimes see are called coefficients

2O2

This coefficient number means there are two lots of the oxygen molecules

O OO O

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

Role playI need

4 Hydrogen's1 Carbon2 oxygen

Methane + Oxygen Carbon dioxide + Water CH4 + O2 CO2 + H2O

Balancing equationsMethane + Oxygen Carbon Dioxide + WaterWhat do you notice about this balanced equation?CH4 + 2O2 CO2 2H2OCCHHHHO OO OO OO O HHHHO OHHHHHHHHHHHHHHHHHO OHHHHO OO OHHHHO OO OO OHHHHO OO OO OHHHHO O OO OO OHHHHHO O OO OO OHHHHHHO O OO OO OHHHHHHHO O OO OO OHHHH

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

Balancing equationsYou are now going to use the molly mod kits to try and balance these equations: 1. H2 + O2 H2O2. Mg + O2 MgO

Balancing equationsTime for you to have a goHydrogen + Oxygen Water H2 + O2 H2O???????HHO ORemember we need to balance it!What do you notice??

Balancing equationsTime for you to have a goHydrogen + Oxygen Water H2 + O2 H2OHHO ORemember we need to balance it!

Why is this wrong??

Because we haven't used both of the oxygen molecules O H H

Balancing equationsTime for you to have a goHydrogen + Oxygen Water H2 + O2 2H2OHHO ORemember we need to balance it, BOTH SIDES

Is this correct??O H HO O O H HO H H

Balancing equationsTime for you to have a goHydrogen + Oxygen Water 2H2 + O2 2H2OHHO ORemember 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 HO O O H HO H HH HH H

Just count up the atoms on each sideThen start balancing:1112The numbers arent balanced so then add BIG numbers to make up for any shortagesAnd adjust totals222

But the numbers still arent equal, so add another BIG number2And adjust totals againNOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMSWE SAY THAT THE EQUATION IS BALANCED!!2

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

YesNoAlmost

PlenaryI 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