Download PowerPoint - Balancing Equations

How molecules are symbolized
Cl2
2Cl
2Cl2
• Molecules may also have brackets to
indicate numbers of atoms. E.g. Ca(OH)2
• Notice that the OH is a group
O Ca O
H
• The 2 refers to both H and O H
• How many of each atom are in the following?
a) NaOH
Na = 1, O = 1, H = 1
b) Ca(OH)2 Ca = 1, O = 2, H = 2
c) 3Ca(OH)2 Ca = 3, O = 6, H = 6
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 Mg + O O  Mg O
• However, this is not balanced
• Left:
Mg = 1, O = 2
• Right: Mg = 1, O = 1
Balance equations by “inspection”
Mg + O2  MgO
2Mg + O2  2MgO is correct
Mg + ½O2

MgO
is
incorrect
Mg2 + O2  2MgO is incorrect
4Mgwith
+ 2elements
O2  4MgO
is incorrect
Hints: start
that occur
in one
compound on each side. Treat polyatomic ions
that repeat as if they were a single entity.
a) P4 + 5 O2  P4O10
b) 2 Li + 2 H2O  H2 + 2 LiOH
c) 2 Bi(NO3)3 + 3 K2S  Bi2S3 + 6 KNO3
d) 2 C2H6 + 7 O2  4 CO2 + 6 H2O
From
Balance the Following Equations
1. __ KNO3  __ KNO2 + __ O2
2. __ Pb(NO3)2  __ PbO + __ NO2 + __ O2
3. __ P4 + __ I2  __ PI3
4. __ MgO + __ H3PO4  __ Mg3(PO4)2 + __ H2O
5. __ Br2 + __ KI  __ I2 + __ KBr
6. __ Ca(OH)2 + __ HNO3  __ Ca(NO3)2 + __ H2O
7. __ Bi2O3 + __ H2  __ Bi + __ H2O
8. __ Fe + __ O2  __ Fe3O4
9. __ CaO + __ C  __ CaC2 + __ CO2