Chapter 8 - Chemical Equations
BALANCING EQUATIONS

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

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
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  +  ___ H2S  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

Get the answers to these problems

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