Honors Chemistry
Notes for 07-07
Balancing Chemical Equations
Page 1 of 5
Balancing by inspection

Most chemical equations we will encounter can be “balanced by inspection.”

This involves a step-by-step approach.

We will use the decomposition of water as our example.

Step 1:
o Identify the names of the reactants and the products, and write a
word equation.
In our example reaction, water is being decomposed into hydrogen
and oxygen.
water  hydrogen + oxygen

Step 2:
o Write a skeleton equation by substituting correct formulas for the
names of the reactants and the products.
H2O(l)  H2(g) + O2(g)

Step 3:
o Balance the skeleton equation according to the law of conservation
of mass.

Step 3a: Balance the different types of atoms one at a time.

Step 3b: First balance the atoms of elements that are combined
and that appear only once on each side of the equation.

Step 3c: Balance polyatomic ions that appear on both sides of
the equation as single units.
Honors Chemistry

Notes for 07-07
Balancing Chemical Equations
Page 2 of 5
Step 3d: Balance H atoms and O atoms after atoms of all other
elements have been balanced.
Let’s look at the H’s first.
H2O(l)  H2(g) + O2(g)
o There are two H’s on the left and two H’s on the right - balanced.
o There is one O on the left and two O’s on the right - unbalanced
o We put a “2” in front of the H2O to balance the O’s.
2 H2O(l)  H2(g) + O2(g)
o We now need to rebalance the H’s.
o We place a “2” in front of the H2 to balance the H’s.
2 H2O(l)  2 H2(g) + O2(g)
o It looks like it’s balanced.

Step 4:
o Count atoms to be sure that the equation is balanced.

On the left –
 4 H’s
 2 O’s

On the right –
 4 H’s
 2 O’s

It’s balanced.
Honors Chemistry
Notes for 07-07
Balancing Chemical Equations
Page 3 of 5
Sample Problem:
The reaction of zinc with aqueous hydrochloric acid produces a solution of zinc
chloride and hydrogen gas. Write a balanced chemical equation for the reaction.
Step 1: Write a word equation:
Step 2: Write the skeleton equation:
Step 3: Balance according to the law of the conservation of mass:

Balance Zn:

Balance Cl:

Balance H:
Step 4: Count the atoms on both sides of the arrow.
Sample Problem:
Solid aluminum carbide, Al4C3, reacts with water to produce methane gas, CH4, and
solid aluminum hydroxide, Al(OH)3,. Write a balanced chemical equation for this
reaction.
Step 1: Write a word equation:
Step 2: Write the skeleton equation:
Step 3: Balance according to the law of the conservation of mass:

Balance Al:

Balance C:

Balance H:

Balance O:
Step 4: Count the atoms on both sides of the arrow.
Honors Chemistry
Notes for 07-07
Balancing Chemical Equations
Page 4 of 5
Sample Problem:
Aluminum sulfate, Al2(SO4)3, and calcium hydroxide, Ca(OH)2, are used in a waterpurification process. When added to water, they dissolve and react to produce two
insoluble products, aluminum hydroxide, Al(OH)3, and calcium sulfate, CaSO4. These
products settle out, taking suspended solid impurities with them. Write a balanced
chemical equation for the reaction.
Step 1: Write a word equation:
Step 2: Write the skeleton equation:
Step 3: Balance according to the law of the conservation of mass:

Balance Al:

Balance SO4:

Balance Ca:

Balance OH:
Step 4: Count the atoms on both sides of the arrow.
Practice Problems:
Balance each of the following chemical equations.
1. Pb(s) + AgNO3(aq) ➜ Ag(s) + Pb(NO3)2(aq)
2. Pb(NO3)2(aq) + KI(aq) ➜ PbI2(s) + KNO3(aq)
3. C3H8(g) + O2(g) ➜ CO2(g) + H2O(l)
4. H2SO4(aq) + NaOH(aq) ➜ Na2SO4(aq) + H2O(l)
Honors Chemistry
Notes for 07-07
Balancing Chemical Equations
5. HgO(s) ➜ Hg(l) + O2(g)
Page 5 of 5