Skill 9.4 Analyzing everyday phenomena in terms of chemical equilibrium

Skill 9.4 Analyzing everyday phenomena in terms of chemical equilibrium 

A system that undergoes no net chemical changes over time is said to be in chemical equilibrium. Generally, this condition occurs when the forward and reverse rates of the chemical reactions taking place in a system are equal. Common phenomena, including many phenomena associated with living organisms, can be analyzed in terms of this concept of chemical equilibrium. Several examples are presented below. 

Many life processes, at the chemical level, require enzymes to catalyze (or accelerate) certain reactions. Enzymes may be able to facilitate reactions in both directions from substrate to products and vice versa. In these cases, the rate of reaction for each direction depends on temperature, pH, concentration of the substrate and products, the presence or absence of enzyme inhibitors, and other factors. A general equation for the enzyme (E), substrate (S) and products (P) is shown below. 

Buffers, such as those used in so-called buffered aspirin (acetylsalicylic acid) for easier digestion, or those needed for maintaining a proper pH for enzyme function in living organisms, can be analyzed in terms of chemical equilibrium. A weakly dissociating acidic compound, for example, reaches equilibrium concentrations in solution. The following chemical equation describes the forward and reverse reactions for the hypothetical weak acid HX in the aqueous state. 

Chemical equilibrium can also be used to help analyze the solubility of solids in a solution. Sodium chloride, or table salt, is a typical example and is characterized by the following chemical equation. 

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