Chemistry Reference
In-Depth Information
Lesson 6-2: Classifying Chemical Reactions
There are, quite literally, millions of types of known chemical reac-
tions. Nobody can be expected to memorize all of these different reac-
tions. Fortunately, many of the known chemical reactions follow patterns
that are similar enough to allow classification. A scheme has been created,
which classifies many of the known reactions into five major categories,
namely:
Synthesis.
Decomposition.
Single replacement.
Double replacement.
Combustion.
Some reactions don't fit neatly into one of these categories, but enough
of them do that the classification scheme is extremely useful. As with all
classification systems, the chemical reaction classification system allows you
to memorize the characteristics of the categories, rather than the individual
reactions.
A synthesis reaction is one where two or more simpler substances com-
bine to form a more complex substance. The reactants may be elements or
compounds. The product, being made up of two or more elements chemi-
cally combined, must be a compound. The general format for a synthesis
reaction is given by the following:
A + B
AB
element
element
compound
or
or
compound
compound
Synthesis reactions are also sometimes called direct combination reac-
tions, or composition reactions.
Examples of Synthesis Reactions
2H
2(g)
+ O
2(g)
2H
2
O
(g)
2CO
(g)
+ O
2(g)
2CO
2(g)
synthesis of water
synthesis of carbon dioxide
4Al
(s)
+ 3O
2(g)
2Al
2
O
3(s)
3H
2(g)
+ N
2(g)
2NH
3(g)
synthesis of aluminum oxide
synthesis of ammonia
