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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
83
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 9
Example Problem 9-2
Writing a Balanced Chemical Equation
Write the balanced chemical equation for the reaction in which solid
sulfur (S) combines with oxygen gas to produce sulfur trioxide gas.
Step 1 Write the skeleton equation.
S(s) ϩ O 2 (g) 0 SO 3 (g)
Step 2 Count atoms of each element in the reactants.
1 S, 2 O
Step 3 Count atoms of each element in the products.
1 S, 3 O
Step 4 Adjust coefficients.
In the formulas O 2 and SO 3 , oxygen is in a 2 to 3 ratio. To balance
O, 3 O 2 are needed for every 2 SO 3 . Insert the coefficients 3 and 2,
respectively.
S(s) ϩ 3O 2 (g) 0 2SO 3 (g)
Now the S atoms must be accounted for. The placement of the
2 before the SO 3 means that there are now 2 S atoms on the right.
There must also be 2 on the left. Place the coefficient 2 in front of
the reactant S.
2S(s) ϩ 3O 2 (g) 0 2SO 3 (g)
Step 5 Write the coefficients in their lowest possible ratio.
The ratio 2:3:2 cannot be written any lower and still produce whole
numbers. The ratio is already the lowest possible.
Step 6 Check your work.
Count the number of atoms of each element on both sides of the
equation and make sure they are equal.
Reactants: 2 S, 6 O
Products: 2 S, 6 O
The numbers are equal, so the equation is correctly balanced.