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
products are on the right

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EXAMPLE #1:        ___ Na  +  ___ Br2 
  ___ 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 
  _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 
  _2_ NaBr
                                       Reactants | Products
                                   Na        2              2
                                   Br        2              2
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EXAMPLE #2:
                   ___ Fe(NO3)2  +  ___ Na3PO4 
  ___ 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 
  ___ Fe3(PO4)2  +  ___ NaNO3
                        reactants | products
                         Fe       3             3
                          NO3       6             1
                        Na       3             1
                       PO4         1             2

 


                   _3_ Fe(NO3)2  +  ___ Na3PO4 
  ___ 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 
  ___ 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 
  ___ HgCl  +  ___ O2

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

3.)    ___ KClO3 
  ___ KCl  +  ___ O2

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

5.)    ___ Al2O3 
  ___ Al  +  ___ O2

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

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

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

9.)    ___ Na2O  +  ___ CO2 
  ___ Na2CO3

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

BALANCING EQUATIONS PRACTICE WORKSHEET

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

2.)        ___ Na  +  ___ I2    ___ NaI

3.)        ___ N2  +  ___ O2    ___ N2O

4.)        ___ N2  +  ___ H2    ___ NH3

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

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

7.)        ___ KClO3    ___ KCl  +  ___ O2

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

9.)        ___ S  +  ___ O2    ___ SO3

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

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

12.)        ___ H2O2    ___ H2O  +  ___ O2

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

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

15.)        ___ Mg(NO3)2  +  ___ K3PO4    ___ 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    ___ Fe2O3
____ 2. ___ Cl2  +  ___ KBr 
  ___ KCl  +  ___ Br2
____ 3. ___ Fe  +  ___ Cu(NO3)2 
  ___ Fe(NO3)3  +  ___ Cu
____ 4. ___ NaCl 
  ___ Na  +  ___ Cl2
____ 5. ___ FeCl3  +  ___ KOH 
  ___ KCl  +  ___ Fe(OH)3
____ 6. ___ KClO3 
  ___ KCl  +  ___ O2
____ 7. ___ Al  +  ___ O2 
  ___ Al2O3
____ 8. ___ Na2S  +  ___ AgNO3 
  ___ Ag2S  +  ___ NaNO3
____ 9. ___ CaCO3 
  ___ CaO  +  ___ CO2
____ 10. ___ Mg  +  ___HCl 
  ___ MgCl2  +  ___ H2
____ 11. ___ Mg(OH)2  +  ___ HCl 
  ___ MgCl2  +  ___ H2O
____ 12. ___ Na2SO4  +  ___ BaCl2 
  ___ BaSO4  +  ___ NaCl
____ 13. ___ C2H2  +  ___O2 
  ___ CO2  +  ___ H2O
____ 14. ___ CaI2  +  ___ F2 
  ___ CaF2  +  ___ I2
____ 15. ___ NaOH 
  ___ Na2O  +  ___ H2O
____ 16. ___ ZnBr2  +  ___ AgNO3 
  ___ AgBr  +  ___ Zn(NO3)2
____ 17. ___ C4H10  +  ___ O2 
  ___ CO2  +  ___ H2O
____ 18. ___ K  +  ___ Br2 
  ___ KBr
____ 19. ___ NaHCO3 
  ___ Na2CO3  +  ___ H2O  +  ___ CO2
____ 20. ___ AgNO3  +  ___ Cu 
  ___ Ag  +  ___ Cu(NO3)2
____ 21. ___ CuSO4  +  ___ NaOH 
  ___ Cu(OH)2  +  ___ Na2SO4
____ 22. ___ Ca(ClO3)2 
  ___ CaCl2  +  ___ O2
____ 23. ___ PH3  +  ___ O2 
  ___ H3PO4
____ 24. ___ H2O  +  ___ Fe 
  ___ H2  +  ___ Fe3O4
____ 25. ___ NO  +  ___ O2 
  ___ 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 dont have to go searching for it.)


ACTIVITY SERIES OF METALS                
Li
Rb
K
Ba
Sr
Ca
Na Replace hydrogen from cold water
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Mg
Al
Mn
Zn
Cr
Fe
Cd Replace hydrogen from steam
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Co
Ni
Sn
Pb
H2 Replace hydrogen from acids
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Sb
Bi
Cu
Hg React with oxygen to form oxides
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Ag
Pt
Au

ACTIVITY SERIES OF HALOGENS
F2
Cl2
Br2
I2


 

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

 

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 Pb + AlCl3 (aluminum has a +3 oxidation number)

 

Balanced 2 Al + 3 PbCl2 3 Pb + 2 AlCl3

 

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

 

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

 

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 theres no reaction.

 

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

 

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 Br2 + AlF3

 

Balanced 2 AlBr3 + 3 F2 3 Br2 + 2 AlF3

 

Here are a few for you to try

 

1. Al + NiBr2
2.    Fe2(SO4) 3 + Ag

3. NaCl + F2

4.     Ba(NO3) 2 + Ni

5. I2 + AlBr3

6.      Ca + KCl

7.      Mg + Zn3(PO4) 2

8.    Na + SnCO3

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

 

sodium nitrate + silver chloride

 

2.

ammonium sulfide + barium nitrate

 

ammonium nitrate + barium sulfide

 

3.

lithium carbonate

 

lithium oxide + carbon dioxide

 

4.

zinc + sulfur

 

zinc sulfide

 

5.

potassium + chlorine

 

potassium chloride

 

6.

magnesium nitride

 

magnesium + nitrogen

 

7.

aluminum + copper (II) sulfate

 

 

 

8.

aluminum + iron (III) bromide

 

 

 

9.

bromine + silver chloride




 

10.

zinc + nickel (II) nitrate

 

 

 

11.

magnesium + silver sulfate

 

 

 

12.

potassium sulfate + aluminum chlorate

 

potassium chlorate + aluminum sulfate

 

13.

ethane (C2H6) + oxygen

 

carbon dioxide + water

 

14.

copper (II) chloride + sodium phosphate

 

copper (II) phosphate + sodium chloride

 

15.

calcium bicarbonate

 

calcium oxide + carbon dioxide + water

 

16.

strontium nitrate + copper (II) sulfate

 

strontium sulfate + copper (II) nitrate

 

17.

magnesium acetate + iron (III) carbonate

 

magnesium carbonate + iron (III) acetate

 

18.

copper (II) phosphate + zinc

 

 

 

19.

potassium + HCl

 

 

 

20.

calcium + potassium chlorate

 

 

 

 

 

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