balancing-equations - How molecules are symbolized Cl2 2Cl...

How molecules are symbolized
Cl
2
2Cl 2Cl
2
•
Molecules may also have brackets to
indicate numbers of atoms. E.g. Ca(OH)
2
O
H
O
H
Ca
•
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
Na = 1, O = 1, H = 1
Ca = 1, O = 2, H = 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 (from lab)
•
Mg + O
2
→ MgO
O Mg O +
→
Mg O
•
However, this is not balanced
•
Left: Mg = 1, O = 2
•
Right: Mg = 1, O = 1

Balance equations by “inspection”
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
2 3 3.5
2 7 4 6
2 2 2
2 6 3
C
2
H
6
+ O
2
→ CO
2
+ H
2
O
a) P
4
+ O
2
→ P
4
O
10
b) Li + H
2
O → H
2
+ LiOH
c) Bi(NO
3
)
3
+