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    ___ 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
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

 

TYPES OF EQUATIONS

DECOMPOSITION:  a compound breaks apart into simpler substances
* To recognize a DECOMPOSITION reaction, look for only 1 REACTANT. *
-----------------------------------------------------------------------------------------------

SYNTHESIS:  2 or more simple substances combine to form one compound;  opposite of
                        decomposition
* To recognize a SYNTHESIS reaction, look for only 1 PRODUCT. *
-----------------------------------------------------------------------------------------------

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. *
-----------------------------------------------------------------------------------------------

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. *
-----------------------------------------------------------------------------------------------

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. *

PREDICTING PRODUCTS OF CHEMICAL REACTIONS

GOAL: to be able to look at the reactants of a chemical equation and tell what the products will be

COMBUSTION REACTIONS

~ How can you recognize the reactants in a combustion reaction?

~ What are the products in a combustion reaction?

* EXAMPLE: ___ C2H4 + ___ O2

DOUBLE REPLACEMENT REACTIONS

~ How do you recognize the reactants in a double replacement reaction?

~ How do you determine the products of a double replacement reaction?

 

* EXAMPLE: ___ Ca(NO3)2 ___ K2CO3

SINGLE REPLACEMENT REACTIONS

~ How do you recognize the reactants in a single replacement reaction?

~ How do you determine what the products are in a single replacement reaction, if there are any
products at all?


~ How is the Activity Series
used with single replacement reactions?

 

* EXAMPLE: ___ Zn + ___ FeCrO4

SYNTHESIS REACTIONS

~ How do you recognize a synthesis reaction by its reactants?

~ How do you decide what the products will be? 


* EXAMPLE: ___ Mg + ___ O2 -->

DECOMPOSITION REACTIONS

~ How can you recognize a decomposition reaction when the reactant(s) are given?

~ How do you determine the products?
* BINARY COMPOUND

* METAL CHLORATE

* METAL CARBONATE

* METAL BICARBONATE

 

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