Type of Reaction

Introduction: There are many kinds of chemical reactions and many ways of classifying them. Most of the reactions talked about in a first year chemistry course can be classified as one of five major types of reactions. These reactions are: synthesis (sometimes called combination); decomposition (sometimes called “analysis” if elements result); single replacement; double replacement, and combustion. These five types of reactions are summarized below. Consult your class notes and text for more information.

Remember, though, that not all chemical reactions can be put into one of these categories. For example, a major group of compounds that undergo other types of reactions is the “organic” compounds (compounds consisting mainly of carbon and hydrogen). While there are many other organic reactions, most undergo combustions. Our study of organic reactions will be limited to combustion reactions.

In a synthesis reaction, a single product (a compound) is formed from two or more simple substances (elements or simple compounds). An example of such a reaction is the formation of water from its elements: 2 H2 + O2 --> 2 H2O.

A decomposition reaction is exactly the opposite of a combination reaction. A single reactant compound breaks down into two or more simpler substances (elements or simpler compounds). The breakdown of a chlorate into oxygen and a chloride salt is one example:

2 NaClO3 ---> 2 NaCl + 3 O2.

In a single replacement reaction, an element (alone in its elemental form) replaces a similar element in a compound. The result is a new element and a new compound. The replacement only occurs if the element that does the replacing is “more active” than the element that gets replaced. Equations for single replacement reactions have two general forms depending on the types of elements involved. In general, metal elements can replace other metals or hydrogen in compounds. Halogen elements may replace other halogens in...