# Balancing Chemical Equations student by cuiliqing

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```									Balancing Chemical Equations
Demonstration!!!!!!!!
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
reaction:
–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
2

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
atom,
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
whole.
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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