11.2. Types of Chemical Reactions http://www.ck12.orgSubstances in all states of matter can participate in combination reactions. For example, oxygen in the air can react
with iron to produce rust. Rusting is a common occurrence, especially in regions of the world where precipitation is
relatively high. Although rust tends to be a mixture of compounds, its primary component is iron(III) oxide (Fe 2 O 3 ).
Rusting is generally a very slow process, but when the iron has a very high surface area, as in the case of steel wool,
it can happen at a much faster rate, as shown in the following video:
http://www.youtube.com/watch?v=5MDH92VxPEQMEDIA
Click image to the left for more content.The balanced chemical equation for this process is shown below:
4Fe(s)+3O 2 (g)→2Fe 2 O 3 (s)Decomposition Reactions
A decomposition reaction is the exact opposite of a combination reaction. In decomposition reactions, a single
chemical species breaks down to produce two or more new chemical species. A generic decomposition reaction
might take the following form:C→A+B
Again, substances in all states of matter commonly participate in decomposition reactions. For example, hydrogen
peroxide will decompose over time to produce water and oxygen gas according to the following equation:
2H 2 O 2 (l)→2H 2 O(l)+O 2 (g)
Another common type of decomposition reaction involves the process of electrolysis, in which an electrical current
is passed through a substance to break apart a compound. One example of a decomposition reaction requiring the
use of electrolysis is the decomposition of molten sodium chloride, as shown by the following equation:
2NaCl(s)→2Na(s)+Cl 2 (g)Single Replacement Reactions
Asingle replacement reaction(sometimes called a single displacement reaction) occurs when one chemical species
(often a single element) replaces a portion of another compound to produce two new products. The general form of
a single replacement reaction is shown below:
AB+C→AC+B
Two common types of single replacement reactions involve pure metals reaction with aqueous solutions of either an
acid or an ionic compound. When a reactive metal is placed in an acid solution, the following reaction is likely to
occur:
Metal + acid→ionic solution + hydrogen gas