Balancing Equations
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Transcript of Balancing Equations
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If a chemical equation does not obey the law ofconservation of mass the equation is said to be what?
NOT BALANCED
So Let’s look at the steps we need to take toBALANCE chemical equations
Fe + O2 Fe2O3
Let’s work with the following equation:
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#R atom #P
1 Fe 22 O 3
For example:
Fe + O2 Fe2O3
Step 1. Create a RAP table (what’s a RAP table ??)
A table that shows us what atoms are present in thisreaction, how many there are and are they 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