Decomposition Reactions
A decomposition reaction is a chemical reaction in which a single compound breaks down into two or
more products. Decomposition reactions can be represented by a general chemical equation and
pictorially as
The products may be a combination of elements and compounds, but the reactant is always a compound.
Decomposition reactions are the opposite of synthesis or formation reactions.
Example:
Water can undergo a decomposition reaction to produce hydrogen gas and oxygen
gas, according to the chemical equation
2H2O(ℓ) + 2H2(g) O2(g)
Understanding
Check your understanding (page 145)
1. Determine whether or not each of the following chemical equations is a combination reaction. Provide an
explanation for each answer.
(a) 2Cr(s) + 3F2(g) → 2CrF3(s)
(b) 2Al(s) + 3SnCl2(aq) → 2AlCl3(aq) + 3Sn(s)
2. Complete and balance the following combination reaction. Predict the state of the product(s).
Ca(s) + N2(g) →
3. Explain why combination reactions are the reverse of decomposition reactions. Use a diagram as part of
your explanation.
4. Complete and balance the following decomposition reaction. Predict the state of the product(s).
AgCl(s) →
Single Replacement Reactions
In a single replacement reaction, an element and a compound react to produce another element and
another compound. The element reacting can be a metal or a non-metal. This type of reaction is one in
which an element takes the place of, or replaces, another element in a compound.
The experiment that we are about to do is an example of a single displacement reaction.