?
Fundamentals of Chemistry
DOE-HDBK-1015/1-93
CHEMICAL EQUATIONS
Rev. 0
CH-01
Page 41
Example:
Explain the following chemical equation.
Solution:
This chemical equation shows that iron reacts with water to form ferric oxide and
hydrogen gas (the vertical arrow ? indicates a gas). This chemical equation also shows
that for every two atoms of iron that react, three molecules of water are used to form
one molecule of ferric oxide and three molecules of hydrogen gas. This is a balanced
chemical equation. There are two iron atoms on each side of the equation; there are six
hydrogen atoms on each side; and there are three oxygen atoms on each side.
There are no fixed rules for balancing chemical equations. Learning how is a matter of practice.
The balancing of most equations can be accomplished by following the guidelines explained
below.
Guidelines:
a.
Once the correct chemical formula for a compound is written in an equation, do
not modify it.
b.
Select the compound with the greatest number of atoms. Then begin by balancing
the element in that compound with the most atoms. There must be the same
number of atoms of an element on each side of the equation. As a rule of thumb,
this first element should not be hydrogen, oxygen, or a polyatomic ion.
c.
Balance the atoms of each element in the compound by placing the appropriate
coefficient in front of the chemical symbol or formula.
d.
Next, balance the polyatomic ions. In some cases, the coefficient assigned in
guideline 2 may have to be changed to balance the polyatomic ion.
e.
Balance the hydrogen atoms next, then the oxygen atoms. If these elements
appear in the polyatomic ion it should not be necessary to balance them again.
f.
All coefficients will be whole numbers. The coefficients should be reduced to the
lowest possible ratios.
g.
As simple as it sounds, check off each element as it is accounted for since this
will prevent double inclusion or a missed atom.
