Chemistry Reference
In-Depth Information
Practice Problem 8.2
Balance an equation for the reaction of octane,
with
C
8
H
18
,
O
2
to yield
CO
2
and H
2
O.
When any element appears in more than one substance on the same side of
the equation, we balance that element last.
EXAMPLE 8.3
Write a balanced equation for the following reaction:
KIO
3
KI
HCl £ I
2
H
2
O
KCl
Solution
Place a 1 before the most complicated-looking formula, and a question
mark before each of the other formulas:
KIO
3
,
1 KIO
3
? KI
? HCl £ ? I
2
? H
2
O
? KCl
Because potassium and iodine appear in two compounds on the left side of the
equation, start working with oxygen, which appears in only one compound on
each side, including the compound with the “1.”
1 KIO
3
? KI
? HCl £ ? I
2
3 H
2
O
? KCl
Knowing how many hydrogen atoms are on the right side of the equation, we
can balance hydrogen next:
1 KIO
3
? KI
6 HCl £ ? I
2
3 H
2
O
? KCl
Now balance chlorine:
1 KIO
3
? KI
6 HCl £ ? I
2
3 H
2
O
6 KCl
K
Balance the potassium, being careful to note that there is already one
in the
1 KIO
3
:
1 KIO
3
5 KI
6 HCl £ ? I
2
3 H
2
O
6 KCl
Finally, balance the iodine:
1 KIO
3
5 KI
6 HCl £ 3 I
2
3 H
2
O
6 KCl
The coefficient 1 may now be deleted:
KIO
3
5 KI
6 HCl £ 3 I
2
3 H
2
O
6 KCl
Check: 6 K, 6 I, 3 O, 6 H, 6 Cl on each side.
Practice Problem 8.3
Balance an equation for the reaction of
with
H
2
O
N
2
O
5
to yield HNO
3
.
EXAMPLE 8.4
Write a balanced equation for the reaction of sodium hydroxide with phosphoric
acid to produce sodium monohydrogen phosphate and water.
