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An example of an exchange reaction is an acid reacting with a base, producing water and a salt. This type of reaction is discussed in the following section.

Many chemical reactions are reversible. This means the product or products can change back to the reactant or reactants. A reversible reaction is symbolized using a double arrow, as follows:

Whether a reversible reaction proceeds in one direction or another depends on such factors as the relative proportions of reactant (or reactants) and product (or products) as well as the amount of energy available. Catalysts are molecules that influence the rates of chemical reactions but are not consumed in the reaction.

Acids, Bases, and Salts

The polarity of water creates a distraction for the ioni-cally bound salts in the internal environment, causing them to dissociate from one another. Sodium chloride (NaCl), for example, ionizes into sodium ions (Na+) and chloride ions (Cl-) when it dissolves (fig. 2.8). This reaction is represented as

Because the resulting solution contains electrically charged particles (ions), it will conduct an electric current. Substances that release ions in water are, therefore, called electrolytes (e-lek'tro-litz). Electrolytes that release hydrogen ions (H+) in water are called acids. For example, in water, the compound hydrochloric acid (HCl) releases hydrogen ions (H+) and chloride ions (Cl-):

Electrolytes that release ions that combine with hydrogen ions are called bases. The compound sodium hydroxide (NaOH) in water releases hydroxyl ions (OH-). The hydroxyl ions, in turn, can combine with hydrogen ions to form water. Thus, sodium hydroxide is a base:

Figure 2.8

The polar nature of water molecules causes sodium chloride (NaCl) to dissolve in water, releasing sodium ions (Na+) and chloride ions (Cl-).

Figure 2.8

The polar nature of water molecules causes sodium chloride (NaCl) to dissolve in water, releasing sodium ions (Na+) and chloride ions (Cl-).

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