1. Balancing Equations:
Chemical and Nuclear

2. Why do we need to Balance Chemical Equations?
The Law of Conservation of Mass
The # of atoms must stay the same on both sides of the equation
The amount of mass is always the same.

3. How do we Balance Chemical Equations?
We use coefficients to balance equations.
Example- 2H2 +O2---> 2H2O
total atoms= H 2-O ---> 4-H 2-O

4. 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

5. 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
Mg + O2  MgO O Mg +  Mg O
However, this is not balanced
Left: Mg = 1, O = 2
Right: Mg = 1, O = 1

6. 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) P4 + O2  P4O10
b) Li + H2O  H2 + LiOH
c) Bi(NO3) K2S  Bi2S KNO3
d) C2H O2  CO H2O 5 2 2 2 2 3 6
3.5 2 3
C2H O2  CO H2O 2 7 4 6

7. 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

8. 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

9. For more lessons, visit www.chalkbored.com
Question 3 pg. 252
a) 2Li + 2H2O ® H2 + 2LiOH
b) P4 + 5O2 ® P4O10
c) 2C2H6 + 7O2 ® 4CO2 + 6H2O
d) CS2 + 3O2 ® CO2 + 2SO2
e) 2AsCl3 + 3H2S ® As2S3 + 6HCl
f) 3AgNO3 + FeCl3 ® 3AgCl + Fe(NO3)3
g) 2KClO3 ® 2KCl + 3O2
h) 2SO2 + O2 ® 2SO3
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