Ways to Classify Reactions

OBJECTIVE To learn various classification schemes for reactions. 

So far in our study of chemistry we have seen many, many chemical reactions—and this is just Chapter 7. In the world around us and in our bodies, literally millions of chemical reactions are taking place. Obviously, we need a system for putting reactions into meaningful classes that will make them easier to remember and easier to understand. 

In Chapter 7 we have so far considered the following driving forces for chemical reactions  

We will now discuss how to classify reactions involving these processes. For example, in the reaction 

So we can classify a reaction such as this one as a precipitation reaction or as a double-displacement reaction. Either name is correct, but the former is more commonly used by chemists. 

Formation of a Solid In the following reaction, solid BaCrO (a precipitate) is formed. 

Because the formation of a solid when two solutions are mixed is called precipitation, we call this a precipitation reaction. 

Notice in this reaction that two anions (N03 and CrO ) are simply 

In this chapter we have also considered reactions in which water is formed when a strong acid is mixed with a strong base. All of these reactions had the same net ionic equation  

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Organic chemistry would just be a vast collection of often seemingly contradictory information if there were no way of classifying reactions. One way to classify reactions is by the overall tranformation, as defined by the relationships of the starting materials and the products. There are four basic kinds of overall transformations addition, elimination, substitution, and rearrangement. 

A second way to classify reactions is according to the type of mechanism that is operative. The mechanism-based method of classification is used to organize the material in this text. However, it is important not to lose the forest (the overall transformation) for the trees (the mechanistic steps). Both classification methods have advantages, and it is useful to be able to move freely between them. 

However, there are still other ways to classify reactions that you may encounter in your future studies of chemistry. We will consider several of these in this section. 

Other Ways to Classify Reactions 189 Chapter Review 193... 

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