The Major Classes of Chemical Reactions

Classifying the Countless There are countless chemical reactions txit only a few reaction classes. These swrtng particles of silver chromate form through one of the three major classes discussed in this chapter. 

Many chemical reactions occur in water. Because of the shape of its molecules and ther cfstributton of electrons, water is a po/ar molecule. In water, many ionic compounds and a few simple covalent compounds, such as HCI, cKssociate into ions. 

To describe an aqueous ionic reaction, chemists use a net ionic equation because it eliminates spectator ions (those not involved in the reaction) and shows the actual chemical change taking place. 

Precipitation reactions occur when soluble ionic compounds exchange ions l/netathesis) and form an insoluble product ipredpitate) in which the ions attract each other so strongly that water cannot pull them apart. 

In solution, an acid produces H ions, and a base produces OH ions, in an acid-base (neutraization) reaction, the and the OH ions form water. Another way to view such a reaction is to see an acid as a substance that transfers a proton (H ) to a base. 

Oxidation is defined as electron loss, and reduction as electron gain. In an oxidation-reduction (redox) reaction, electrons move from one reactant to the other the reducing agent is oxidized (loses electrons), and the oxidizing agent is reduced (gains electrons). Chemists use oxidation numbers, the numbers of electrons owned by the atoms in reactants and products, to follow these changes. 

Many common redox reactions involve elements as reactants or products. In an activity series, metals are ranked according to their ability to displace H2 (reduce H ) from water or acid or reduce the cation of another metal from solution. 

Polar Nature of Water Ionic Compounds in Water Covalent Compounds in Water 

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The third of the major classes of chemical reaction are the redox reactions. These reactions are of extraordinary versatility. Many common reactions, like combustion, corrosion, photosynthesis, the metabolism of food, and the extraction of metals from their ores look completely different superficially but to a chemist s eye, they are all aspects of a single type of event. Once again, we see how chemistry gives us eyes to see the extraordinary complexity of the world as the outcome of much simpler events going on below the surface. 

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