# UNIT 8 - Chemical Equations BALANCING EQUATIONS NOTES

Q: WHY DO WE NEED TO BALANCE CHEMICAL EQUATIONS?
A: The LAW OF CONSERVATION OF MASS says that matter cannot be created or destroyed.  In other words, you
cannot end up with any more or any less than you started with.

Q: HOW DO YOU BALANCE AN EQUATION?
A: (1) Count up the number of atoms of each element (or polyatomic ion) on each side of the arrow in the
equation (eqn).
(2) Use coefficients (numbers in FRONT of the element or compound) to balance the numbers on either side of
the eqn.
(3) Do not ever change subscripts (formulas) in a compound!

Q: WHAT ARE "REACTANTS" & "PRODUCTS"?
A: In a chemical eqn,    reactants are on the left side of the arrow
à products are on the right

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EXAMPLE #1:        ___ Na  +  ___ Br2
à  ___ NaBr
STEP 1: Set up a chart with # of atoms of each element on each side of eqn.
Reactants | Products
Na        1             1
Br         2             1
STEP 2: Balance one of the elements that is not balanced.  In this case, that is the Br.
(Reactant side has more than product side, so coefficient should go on the product side.)
___ Na  +  ___ Br2
à  _2_ NaBr
* Reminder: the coefficient gets multiplied by subscripts of all elements in the compound it
is in front of. *
Reactants | Products
Na       1              2
Br        2              2
STEP 3: Check all elements to see if they are balanced.  Na is not balanced, so it needs a coefficient of 2.
_2_ Na  +  ___ Br2
à  _2_ NaBr
Reactants | Products
Na        2              2
Br        2               2
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EXAMPLE #2:
___ Fe(NO3)2  +  ___ Na3PO4
à  ___ Fe3(PO4)2  +  ___ NaNO3
reactants | products
Fe            1                3
NO3          2                1
Na           3                1
PO4         1                2
* because there is oxygen in every compound in the equation, it may be helpful to count the number of a polyatomic ion, rather than splitting the polyatomic ion into its elements and then counting.*
_3_ Fe(NO3)2  +  ___ Na3PO4
à  ___ Fe3(PO4)2  +  ___ NaNO3
reactants | products
Fe          3             3
NO3        6             1
Na          3             1
PO4         1             2

_3_ Fe(NO3)2  +  ___ Na3PO4
à  ___ Fe3(PO4)2  +  _6_ NaNO3
reactants | products
Fe          3             3
NO3        6             6
Na          3             6
PO4         1             2

_3_ Fe(NO3)2  +  _2_ Na3PO4
à  ___ Fe3(PO4)2  +  _6_ NaNO3
reactants | products
Fe          3             3
NO3        6             6
Na          6             6
PO4         2             2
Finished!

Now, you try these examples:

1.)    ___ HgO  +  ___ Cl2
à  ___ HgCl  +  ___ O2

2.)    ___ C3H8  +  ___ O2
à  ___ CO2  +  ___ H2O
**HINT: Balance the H's and O's last.**

3.)    ___ KClO3
à  ___ KCl  +  ___ O2

4.)    ___ Ca(OH)2  +  ___ HNO3
à  ___ Ca(NO3)2  +  ___ H2O

5.)    ___ Al2O3
à  ___ Al  +  ___ O2

6.)    ___ CuCl2  +  ___ H2
à  ___ CuS  +  ___ HCl

7.)    ___ Cl2  +  ___ NaBr
à  ___ NaCl  +  ___ Br2

8.)    ___ NaOH  +  ___ HCl
à  ___ NaCl  +  ___ H2O

9.)    ___ Na2O  +  ___ CO2
à  ___ Na2CO3

10.)    ___ H2O  +  ___ Fe
à  ___ Fe2O3  +  ___ H2

BALANCING EQUATIONS PRACTICE WORKSHEET

1.)        ___ CH4  +  ___ O2  à  ___ CO2  +  ___ H2O

2.)        ___ Na  +  ___ I2  à  ___ NaI

3.)        ___ N2  +  ___ O2  à  ___ N2O

4.)        ___ N2  +  ___ H2  à  ___ NH3

5.)        ___ KI  +  ___ Cl2  à  ___ KCl  +  ___ I2

6.)        ___ HCl  +  ___ Ca(OH)2  à  ___ CaCl2  +  ___ H2O

7.)        ___ KClO3  à  ___ KCl  +  ___ O2

8.)        ___ K3PO4  +  ___ HCl  à  ___ KCl  +  ___ H3PO4

9.)        ___ S  +  ___ O2  à  ___ SO3

10.)        ___ KI  +  ___ Pb(NO3)2  à  ___ KNO3  +  ___ PbI2

11.)        ___ CaSO4  +  ___ AlBr3  à  ___ CaBr2  +  ___ Al2(SO4)3

12.)        ___ H2O2  à  ___ H2O  +  ___ O2

13.)        ___ Na  +  ___ H2à  ___ NaOH  +  __ H2

14.)        ___ C2H6  +  ___ O2  à  ___ CO2  +  ___ H2O

15.)        ___ Mg(NO3)2  +  ___ K3PO4  à  ___ Mg3(PO4)2  +  ___ KNO3

TYPES OF EQUATIONS NOTES

DECOMPOSITION:  a compound breaks apart into simpler substances
* To recognize a DECOMPOSITION reaction, look for only 1 REACTANT. *
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SYNTHESIS:  2 or more simple substances combine to form one compound;  opposite of
decomposition
* To recognize a SYNTHESIS reaction, look for only 1 PRODUCT. *
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SINGLE REPLACEMENT:  an element reacts with a compound to form a new element &
a new compound
* To recognize a SINGLE REPLACEMENT reaction, look for one element and one
compound as the reactants. *

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COMBUSTION:  an organic compound (usually a hydrocarbon) combines with oxygen to
produce carbon dioxide and water
* To recognize a COMBUSTION reaction, the reactants will be an organic compound and
oxygen. *

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DOUBLE REPLACEMENT:  a compound reacts with another compound to form 2 new
compounds
* To recognize a DOUBLE REPLACEMENT reaction, look for 2 compounds as the
reactants. *
REACTION TYPES WORKSHEET

--> Balance each equation.
--> Identify the type of reaction as:            * S - synthesis                * D - decomposition
* C – combustion                       * SR - single replacement                * DR - double replacement
TYPE
____ 1. ___ Fe  +  ___ O2  à  ___ Fe2O3
____ 2. ___ Cl2  +  ___ KBr
à  ___ KCl  +  ___ Br2
____ 3. ___ Fe  +  ___ Cu(NO3)2
à  ___ Fe(NO3)3  +  ___ Cu
____ 4. ___ NaCl
à  ___ Na  +  ___ Cl2
____ 5. ___ FeCl3  +  ___ KOH
à  ___ KCl  +  ___ Fe(OH)3
____ 6. ___ KClO3
à  ___ KCl  +  ___ O2
____ 7. ___ Al  +  ___ O2
à  ___ Al2O3
____ 8. ___ Na2S  +  ___ AgNO3
à  ___ Ag2S  +  ___ NaNO3
____ 9. ___ CaCO3
à  ___ CaO  +  ___ CO2
____ 10. ___ Mg  +  ___HCl
à  ___ MgCl2  +  ___ H2
____ 11. ___ Mg(OH)2  +  ___ HCl
à  ___ MgCl2  +  ___ H2O
____ 12. ___ Na2SO4  +  ___ BaCl2
à  ___ BaSO4  +  ___ NaCl
____ 13. ___ C2H2  +  ___O2
à  ___ CO2  +  ___ H2O
____ 14. ___ CaI2  +  ___ F2
à  ___ CaF2  +  ___ I2
____ 15. ___ NaOH
à  ___ Na2O  +  ___ H2O
____ 16. ___ ZnBr2  +  ___ AgNO3
à  ___ AgBr  +  ___ Zn(NO3)2
____ 17. ___ C4H10  +  ___ O2
à  ___ CO2  +  ___ H2O
____ 18. ___ K  +  ___ Br2
à  ___ KBr
____ 19. ___ NaHCO3
à  ___ Na2CO3  +  ___ H2O  +  ___ CO2
____ 20. ___ AgNO3  +  ___ Cu
à  ___ Ag  +  ___ Cu(NO3)2
____ 21. ___ CuSO4  +  ___ NaOH
à  ___ Cu(OH)2  +  ___ Na2SO4
____ 22. ___ Ca(ClO3)2
à  ___ CaCl2  +  ___ O2
____ 23. ___ PH3  +  ___ O2
à  ___ H3PO4
____ 24. ___ H2O  +  ___ Fe
à  ___ H2  +  ___ Fe3O4
____ 25. ___ NO  +  ___ O2
à  ___ NO2

PREDICTING WHETHER A SINGLE REPLACEMENT REACTION WILL OCCUR NOTES

The reactants in a single replacement reaction are an element (by itself) and a compound.  Some single replacement reactions will happen, others will not.  In order to determine if a single replacement reaction will occur, you must use the Activity Series.  (It is located on page 7 of the Reference Tables, but I have included one here so you don’t have to go searching for it.)

# ACTIVITY SERIES OF HALOGENSF2                                Cl2                                Br2                                I2

EXAMPLE 1 – Will the following reaction happen or not?                             Al  +  PbCl2 à

Step 1 – Look at the element by itself.  Is this element a metal or a nonmetal?  Al (aluminum) is a metal because it is located to the left side of the staircase line on the Periodic Table.
Step 2 – You will compare the type of element by itself to the similar type of element in the compound.  In this case, aluminum is a metal, so I will compare it with the metal in the compound (which is Pb).

Step 3 – RULE:  The element that is by itself must be HIGHER on (closer to the top of) the Activity Series for the reaction to happen!  In this case…

Al             (by itself)
Mn
Zn
Cr

Fe
Cd                                                           Replace hydrogen from steam
--------------------------------------------------------------------------------------------------------------------
Co
Ni
Sn
Pb            (in compound)

Aluminum (Al) is higher than lead (Pb), so the reaction happens.

What are the products of the reaction?

Aluminum and lead “switch places”.  However, remember to use the oxidation numbers of the elements to write the formulas.  Then, balance the equation.

Al  +  PbCl2  à  Pb  +  AlCl3                  (aluminum has a +3 oxidation number)

Balanced…        2 Al  +  3 PbCl2  à  3 Pb  +  2 AlCl3

EXAMPLE 2 – Will the following reaction happen or not?                             Fe + Mg(NO3)2  à

Answer:  Iron (Fe) needs to be higher on the Activity Series than magnesium (Mg) in order for the reaction to occur.  It is not, so there is no reaction.

EXAMPLE 3 – Will the following reaction happen or not?                             NaCl  +  Br2  à

Answer:  Br2 is the element by itself.  It is a nonmetal, so I have to compare it to the nonmetal in the compound – which is Cl.  Br needs to be higher than Cl in order for the reaction to happen.  It is not, so there’s no reaction.

EXAMPLE 4 – Will the following reaction happen or not?                             AlBr3  +  F2  à

Answer:  F2 is the element by itself.  It is a nonmetal, so I have to compare it to the nonmetal in the compound – which is Br.  F needs to be higher than Br in order for the reaction to happen.  It is, so the reaction happens.  Fluorine and bromine “switch places”.  Remember to use the oxidation numbers of the elements to write the formulas.  Also, remember that fluorine, chlorine, bromine, and iodine are DIATOMIC – that means that these elements will have a subscript of 2 when they are by themselves.

AlBr3  +  F2  à  Br2  +  AlF3

Balanced…        2 AlBr3  +  3 F2  à  3 Br2  +  2 AlF3

Here are a few for you to try…

1.         Al  +  NiBr2  à
2.         Fe2(SO4) 3  +  Ag
à
3.         NaCl  +  F2
à
4.         Ba(NO3) 2  +  Ni
à
5.         I2  +  AlBr3
à
6.         Ca  +  KCl
à
7.         Mg  +  Zn3(PO4) 2
à
8.         Na  +  SnCO3
à

Unit 8 Review Worksheet (Honors level)

(A)    Write the reaction using formulas (reactants and products).

(B)    Balance the equation and tell the type of reaction.

 Reactants Products Type of Eqn. 1. silver nitrate + sodium chloride à sodium nitrate + silver chloride 2. ammonium sulfide + barium nitrate à ammonium nitrate + barium sulfide 3. lithium carbonate à lithium oxide + carbon dioxide 4. zinc + sulfur à zinc sulfide 5. potassium + chlorine à potassium chloride 6. magnesium nitride à magnesium + nitrogen 7. aluminum + copper (II) sulfate à 8. aluminum + iron (III) bromide à 9. bromine + silver chloride à 10. zinc + nickel (II) nitrate à 11. magnesium + silver sulfate à 12. potassium sulfate + aluminum chlorate à potassium chlorate + aluminum sulfate 13. ethane (C2H6) + oxygen à carbon dioxide + water 14. copper (II) chloride + sodium phosphate à copper (II) phosphate + sodium chloride 15. calcium bicarbonate à calcium oxide + carbon dioxide + water 16. strontium nitrate + copper (II) sulfate à strontium sulfate + copper (II) nitrate 17. magnesium acetate + iron (III) carbonate à magnesium carbonate + iron (III) acetate 18. copper (II) phosphate + zinc à 19. potassium + HCl à 20. calcium + potassium chlorate à