1. Balancing Equations:

2. How molecules are symbolized
Cl Cl Cl2
Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2
Notice that the OH is a group
The 2 refers to both H and O
How many of each atom are in the following?
a) NaOH
b) Ca(OH)2
c) 3Ca(OH)2 O H Ca
Na = 1, O = 1, H = 1
Ca = 1, O = 2, H = 2
Ca = 3, O = 6, H = 6

3. Balancing equations: MgO
The law of conservation of mass states that matter can neither be created or destroyed
Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction
Thus, the number of a particular atom is the same on both sides of a chemical equation
Example: Magnesium + Oxygen (from lab)
Mg + O2  MgO O Mg +  Mg O
However, this is not balanced
Left: Mg = 1, O = 2
Right: Mg = 1, O = 1

4. Balance equations by “inspection”
From Mg + O2  MgO
2Mg + O2  2MgO is correct
Mg + ½O2  MgO is incorrect
Mg2 + O2  2MgO is incorrect
4Mg + 2 O2  4MgO is incorrect
Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity.

5. Here are some more to balance:
a) 2KNO3  2KNO2 + O2
b) 2Pb(NO3)2  2PbO + 4NO2 + O2
c) P4 + 6I2  4PI3
d) 3MgO + 2H3PO4  Mg3(PO4)2 + 3H2O
e) Br2 + 2KI  I2 + 2KBr
f) Ca(OH)2 + 2HNO3  Ca(NO3)2 + 2H2O
g) Bi2O3 + 3H2  2Bi + 3H2O
h) 3Fe + 2O2  Fe3O4
i) 2CaO + 5C  2CaC2 + CO2