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Chemical equation must obey the law of conservation of mass. According to the Law, mass cannot be created or destroyed

BALANCED OR NOT BALANCED?Mass of reactants: molar mass of Fe + 2(molar mass of O)= 55.85 g + 2X 16 g = 56 g + 32 g= 88 gMass of products: 2X 56 g + 3X 16g= 160 gMass of reactants < mass of productsNOT BALANCED

Fe + O2 Fe2O3

Let’s look at the following equation:

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#R atom #P

1 Fe 22 O 3

For example:

Fe + O2 Fe2O3

So how do we balance?

Step 1. Create a RAP table that shows how many elements are there as reactantsor products?

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#R atom #P

1 Fe 22 O 3

Rule 2. Go to the first atom that’s not balanced and balance it!

Since Fe atoms are not balanced what do we need to do to balance it?

Right! Multiply it by 2 (Only multiply)

2x

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#R atom #P

1 Fe 22 O 3

2Fe + O2 Fe2O3

In step 2 we balanced the number of Fe atoms by multiplying the reactant side by 2. This now becomes the new coefficient in the chemical equation.

Modify the equation to reflect the change

Are all atoms balanced?

2x

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#R atom #P

2 Fe 2 2 O 3

2Fe + 3O2 2Fe2O3

3. Move to the next unbalanced atom. What is it?

How can we balance the Oxygen?

#R atom #P

2 Fe 23x2 O 3x2

Adjust the equation to reflect yourchanges

But notice that by changing Oxygen we alsoChanged Iron. We need to go back and fix this.

Multiply Reactants by 3 and Products by 2

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#R atom #P

2 Fe 4 6 O 6

4Fe + 3O2 2Fe2O3

4. Write out the updated RAP table. How can we Balance the Iron?

Sure! Multiply the # of Reactant Fe atoms by 2 !

Do we have a balanced Chemical Equation now?

2x

Re-write the equation reflectingThe new changes you’ve made.

Yes we do!

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PolyatomicsPolyatomicsWhen an equation has Polyatomics in it, such as in thisBalanced chemical equation

2AgNO3 + MgCl2 2AgCl + Mg(NO3)2

And the polyatomic appears on BOTH the reactant and productSide of the equation Count the polyatomic as an “ATOM”

So the above reactant atoms would be: #R atom #P

2 Ag 22 NO3 21 Mg 12 Cl 2

If the same polyatomic does notAppear on both sides break the Polyatomic down into atoms!

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#R atom #P

1 NA 11 OH 21 Ca 12 Br 1

Is this equation balanced?

NaOH + CaBr2 Ca(OH)2 + NaBr

What atoms do we have inThis equation?

1) Count atoms & Start the RAP table

2) Do the #Reactant atoms = the # of Product atoms?

3) So pick the 1st unbalanced atom & begin balancing

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#R atom #P

1 Na 11 OH 21 Ca 12 Br 1

We’ll start with balancing Hydroxide

NaOH + CaBr2 Ca(OH)2 +NaBr

How can we make both Hydroxides equal?

Sure we’ll multiply #R OH by 2

2x

Hydroxide is now balanced so let’s move to the nextUnbalanced atom, which is? …

Next step> rewrite the modified eqn.

2NaOH + CaBr2 Ca(OH)2 + NaBr

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#R atom #P

2 Na 12 OH 21 Ca 12 Br 1

What can we do to balance the Bromine?

2NaOH + CaBr2 Ca(OH)2 + 2NaBr

Now adjust the table to reflectThe changes and then rewrite theEqn.

Sure! Multiply the #P Bromine by 2

x2

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#R atom #P

2 Na 22 OH 21 Ca 12 Br 2

Let’s update the RAP table with the new #’sBased on our updated equation.

2NaOH + CaBr2 Ca(OH)2 + 2NaBr

Are we now balanced?

Sure!

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#R atom #P

2 C 16 H 22 O 3

Ok Try Balancing this equation:

C2H6 + O2 CO2 + H2O

Step 2. Balance the #P Carbon

#R atom #P

2 C 26 H 22 O 5

C2H6 + O2 2CO2 + H2O

Step 1. Total up the atoms

& Re-write the equation

Are we done?

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#R atom #P

2 C 26 H 22 O 5

C2H6 + O2 2CO2 + 3H2O#R atom #P

2 C 26 H 62 O 7

Step 3. Carbons are balanced now but Hydrogen isn’t. So, balance Hydrogen atoms next

Carbon and Hydrogen are nowbalanced but oxygen isn’t.

Multiply #P Hydrogen by 3

Step 4. Re-write the eqn. & Retotal the number of atoms

x3

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C2H6 + 3½ O2 2CO2 + 3H2O

#R atom #P

2 C 26 H 62 O 7

Step 5. To balance Oxygen multiply O by 3½

Step 6. Re-write the eqn. & Retotal the number of atoms

It looks like we’re balanced. But, are we? No! We can’t have 3 ½ Oxygen molecules! Only wholeNumbers are allowed.

So what do we need to do to fix this?

3 ½ x

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C2H6 + 3½ O2 2CO2 + 3H2O

#R atom #P

4 C 412 H 1214 O 14

Step 7. Let’s clean this up by Multiply everything by 2

Step 8. Retotal #R and the #P atoms

2C2H6 + 7 O2 4CO2 + 6H2O

Are we balanced? YES!

x 2

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Try this problem

NH4OH + FeCl3 Fe(OH)3 + NH4Cl

#R atom #P

1 NH4 11 OH 31 Fe 13 Cl 1

Start here. Recognize weHave polyatomics but theyAppear on both sides of theEquation.

OK … Now finish it up

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Answer to previous problemAnswer to previous problem

3NH4OH + FeCl3 Fe(OH)3 + 3NH4Cl