1. Balancing Equations:
Chemical and Nuclear

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.
a) P O2  P4O10
b) Li + H2O  H2 + LiOH
c) Bi(NO3) K2S  Bi2S KNO3
d) C2H O2  CO H2O 5
1,5,1 b, 2,2,1,2 c 2,3,1,6, d 2,7,2,3 2 2 2 2 3 6
3.5 2 3
C2H O2  CO H2O 2 7 4 6

5. Balance these skeleton equations:
a) Mg +__ HCl  MgCl2 + H2
b) __Ca + N2  Ca3N2
c) NH4NO3  N2O + __H2O
d) __BiCl3 + __H2S  Bi2S3 + __HCl
e) __C4H10 + __O2  __CO2 + __H2O
f) _O2 + C6H12O6  __CO2 + __H2O
g) __NO2 + H2O __HNO3 + NO
h) Cr2(SO4)3+ _NaOH  _Cr(OH)3+ _Na2SO4
i) Al4C3 + __H2O  _CH4 + _Al(OH)3

6. Balance these skeleton equations:
a) Mg + 2HCl  MgCl2 + H2
b) 3Ca + N2  Ca3N2
c) NH4NO3  N2O + 2H2O
d) 2BiCl3 + 3H2S  Bi2S3 + 6HCl
e) 2C4H O2  8CO2 + 10H2O
f) 6O2 + C6H12O6  6CO2 + 6H2O
g) 3NO2 + H2O  2HNO3 + NO
h) Cr2(SO4)3+ 6NaOH  2Cr(OH)3+ 3Na2SO4
i) Al4C3 + 12H2O  3CH4 + 4Al(OH)3

7. Returning to reaction typesK Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
We have looked at several types of reactions without worrying about balancing
However, all equations should be balanced
Predict the products and balance these:
(recall, metals above replace metals below, reactions with water yield metal hydroxides)
Cu + Fe2(SO4)3
Fe + CuSO4  2 3 3
Ni + NaCl 
NR (no reaction)
Al + CuCl2  2 3 3
Cu AlCl3 2
Li + ZnCO3  2
Zn Li2CO3
Li + H2O  2 2 2
LiOH H2
Al + O2  4 3 2
Al2O3

8. Returning to reaction typesK Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
We have looked at several types of reactions without worrying about balancing
However, all equations should be balanced
Predict the products and balance these:
(recall, metals above replace metals below, reactions with water yield metal hydroxides)
Fe + CuSO4 
Ni + NaCl 
Al + CuCl2 
Li + ZnCO3 
Li + H2O 
Al + O2 