Balancing Chemical Equations student by cuiliqing


									Balancing Chemical Equations
Sentence - Combine dissolved Lead (II) Nitrate with aqueous Potassium
  Iodide to yield aqueous Potassium Nitrate and solid Lead (II) Iodide

Word - ____

Chemical- _____

This is called a double displacement reaction  more
  on this to come.
  Balanced Chemical Equations
• Atoms can’t be created or destroyed in a
   –All the atoms we _________we must
    ___________(meaning: balanced!)
• A balanced equation has the same
  number of each element
  __________of the equation.
                 Chemical Reactions
While the reactions show what is used up and what is produced, they do not
  reflect the proper number of each type of atom required for the reaction.

2 H +      O2  2 H2O

How many oxygen atoms are on the right?
How many oxygen atoms are on the left?
Does this make sense? What happened to that other oxygen atom.
We use coefficients to “balance the equation” ensure that there are the same
   number of each type of atom on either side of the equation.
Afterwards check to make sure the number of atoms on the left = the right

**Using coefficients doesn’t change the reaction, it simple shows us how
   many atoms were actually involved**
         Rules for balancing:
1) Assemble the _____________ for all the
   reactants and products, using “+” and “→”
2) Count the number of atoms of each type
   appearing on both sides
3) Balance the elements one at a time by adding
   coefficients (the numbers in front) where you
   need more -
   (hint: I prefer to save O until the very last)
4) _________ to make sure it is balanced by
   counting the atoms on both sides.
• _______change a subscript to balance an
  equation (You can only change coefficients)
  – If you change the subscript (formula) you are
    describing a different chemical.
  – H2O is a different compound than H2O2
• _______ put a coefficient in the middle of a
  formula; they must go only in the _______
       __NaCl is okay, but Na__Cl is not.
                    Chemical Reactions
                                          Element   Before   After

                                          C         1        1
In more complicated chemical reactions,
                                          H         4        2
    we may want to use a chart to keep
    track of the number of each kind of   O         2        3
                                          Element   Before   After

CH4 + _ O2         CO2 +    _ H2O        C         1        1

                                          H         4        4
Now lets count the atoms,
                                          O         2        4
To balance Hydrogen.
                                          Element   Before   After
Try putting a 2 in front of the H2O
To balance Oxygen                         C         1        1
Try putting a 2 in front of the oxygen
                                          H         4        4

                                          O         4        4
                  Chemical Reactions

Some more practice.

       N2 +              __ H2          __ NH3
If there is a polyatomic that sticks together than you can balance it as a
       Pb(NO3)2+ __ KI  PbI2 +            __ KNO3

 __ NaHCO3 +      H2SO4       Na2SO4 +     __ H2O +        __   CO2
 Practice Balancing Examples
• _AgNO3 + _Cu  _Cu(NO3)2 + _Ag

• _Mg + _N2  _Mg3N2

• _P + _O2  _P4O10

• _Na + _H2O  _H2 + _NaOH

• _CH4 + _O2  _CO2 + _H2O

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