Types of Reactions

The many kinds of reactions you may encounter can be placed into four basic categories: combination, decomposition, single replacement, and double replacement.

The first type, combination, can also be called synthesis. This means the formation of a compound from the union of its elements. Some examples of this are:

Zn + S ---> ZnS

2H2 + O2 ---> 2H20

C + O2 ---> CO2

The second type of reaction, decomposition, can also be referred to as analysis. This means the breakdown of a compound to release its components as individual elements or other compounds. Some examples of this type are:

2H2O ---> 2H2 + O2 (electrolysis of water)

C12H22O11 ---> 12C + 11H2O

2HgO ---> 2Hg + O2

The third type of reaction is called single replacement or single displacement. This type can best be shown by examples in which one substance is displacing another. Some examples are:

Fe + CuSO4 ---> FeSO4 + Cu

Zn + H2SO4 ---> ZnSO4 + H2

Cu + 2AgNO3 ---> Cu(NO3)2 + 2Ag

The last type of reaction is called double replacement or double displacement because there is an actual exchange of "partners" to form new compounds. Some examples of this are:

AgNO3 + NaCl ---> AgCl + NaNO3

H2SO4 + 2NaOH ---> Na2SO4 + 2H2O (neutralization)