Name ______________________________ Class ______________ Date __________
Combination and Decomposition Reactions
Step-by-Step Practice
1. Write a balanced equation for the combination of
potassium and chlorine.
K(s) + Cl2(g) →
1. Analyze Identify the relevant concepts.
Potassium is in Group 1A on the periodic table. Chlorine
is in Group 7A.
For Problem 1, students are
provided a framework and
the necessary work for each
step. For Problem 2, they are
given a framework but must
do some of the work
themselves.
2. Solve Apply the concepts to this problem.
Identify the binary ionic compound that can be formed by the
combination of potassium and chlorine. This compound is
potassium chloride. Write the symbol and charge for each ion
in the compound. Then write the formula for the product.
Ions Product
K+
KCl
Cl–
Write a skeleton equation for the reaction. Check to see if
the equation is balanced as written. It is not balanced
because there are more chlorine atoms on the left side of
the equation than on the right.
K(s) + Cl2(g) → KCl(s)
Add a coefficient to the product to balance chlorine.
K(s) + Cl2(g) → 2KCl(s)
Now there are more potassium atoms on the right side
than on the left side. Add za coefficient in front of K(s) to
finish balancing the equation.
2K(s) + Cl2(g) → 2KCl(s)
2. Write a balanced equation for the decomposition of aluminum chloride.
AlCl3(s) →
1. Analyze Identify the relevant concepts.
The elements that make up aluminum chloride are aluminum and chlorine. Aluminum is
a solid. Chlorine is a gas that is found as a diatomic molecule.
Chemistry Skills and Math Workbook •
Name ______________________________ Class ______________ Date __________
2 Solve Apply the concepts to this problem.
Write the formula for each product.
Products
Al(s)
Cl2(g)
Write a skeleton equation for the reaction.
AlCl3(s) → Al(s) + Cl2(g)
Explain why the equation is not balanced as written.
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Add coefficients to balance the equation.
On Your Own
2 AlCl3(s) →
Al(s) +
Cl2(g)
3. Chromium(III) oxide (Cr2O3) is a solid compound that is used in some paints. Complete
the decomposition equation for the reaction. Then balance the equation.
Cr2O3(s) →
4. Lithium phosphide (Li3P) is a compound used in the production of lasers for barcode
scanners. Write and balance an equation for the combination of lithium and phosphorous
solids that produces lithium phosphide gas.
5. Write and balance the equation for the combination reaction that produces solid gold(III)
chloride (AuCl3) from solid gold and chlorine gas.
Chemistry Skills and Math Workbook •