Chemistry Reference
In-Depth Information
A decomposition reaction occurs when a more complex substance breaks
down into two or more simpler substances. In this type of reaction, the
reactant must be a compound, and the products can be either elements or
compounds. The general format for a decomposition reaction is:
AB
A + B
compound
element
element
or
or
compound
compound
As you can see, the format for the decomposition reaction is the oppo-
site of the format for the synthesis reaction. Another common name for a
decomposition reaction is analysis.
Examples of Decomposition Reactions
CaCO
3(s)
CaO
(s)
+ CO
2(g)
2NH
3(g)
3H
2(g)
+ N
2(g)
decomposition of calcium carbonate
decomposition of ammonia
2HgO
(s)
2Hg
(l)
+ O
2(g)
2H
2
O
(l)
2H
2(g)
+ O
2(g)
decomposition of mercury (II) oxide
decomposition of water
A single replacement reaction occurs when an element reacts with a com-
pound in such a way that the element replaces an ion of a similar element
from the compound. In order for the replacement to occur, the elemental
reactant must be more reactive than the elemental product. The general
format for a single displacement reaction, when the elemental reactant is a
metal, is:
A + BC
AC + B
element + compound
compound + element
When the elemental reactant is a nonmetal, the general format looks
more like this:
A + BC
BA + C
element + compound
compound + element
What is the difference, you might ask? The elemental reactant will re-
place the part of the compound that it is most like. You won't see a metal
replacing a nonmetal to form a compound like AgCu. Remember that things
with like charges will repel each other, so you won't make compounds out
of things with similar oxidation numbers. Single replacement reactions are
also called single displacement reactions.
