7.5 Equilibrium
Reading Focus
Key Concepts
Under what conditions do physical and chemical equilibria occur?- How do equilibrium systems respond to change?
Vocabulary
equilibrium
reversible reaction
Reading Strategy
Outlining As you read, make an outline of the most important ideas in this section.
Equilibrium
Types of Equilibria
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Temperature
Pressure
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Figure 24 About 190,000 vehicles pass through the toll plaza of New York City's Verrazano-Narrows Bridge every day.
Suppose you're waiting in line for a toll booth at a bridge, like some of the cars shown in Figure 24. You notice that every time a car passes by a toll booth in the direction you are traveling, another car passes through the toll plaza in the opposite direction. The rate of cars entering equals the rate of cars exiting. As a result, the number of cars on either side of the toll plaza remains constant, although cars are continually entering and exiting the bridge.
Types of Equilibria
The traffic at a toll bridge is similar to a system in equilibrium. Equilibrium (plural equilibria) is a state in which the forward and reverse paths of a change take place at the same rate.
Recall that changes to matter are either physical or chemical. When opposing physical changes take place at the same rate, a physical equilibrium is reached. When opposing chemical changes take place at the same rate, a chemical equilibrium is reached.
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