Module 7

Module 7—Principles of Chemical Equilibrium

Read

For equilibrium systems containing gases, a change in the volume of the system can also be a stress that will bring about a shift in equilibrium. Read page 694 of the textbook to learn about the effect that a change in volume and the addition of a catalyst can have on the equilibrium of a system. As you read this section you may wish to recall the pressure–volume relationship you learned about in previous science courses—a halving of the volume of a fixed quantity of gas results in a doubling of the gas’ pressure.

There are three main changes that can affect the equilibrium in a chemical system: concentration change, temperature change, and volume (or pressure) change.

• Concentration change: An increase in concentration causes a shift to consume some of the added reactant or product. A decrease in concentration causes a shift to produce some of the removed reactant or product.
  
  
• Temperature change: An increase in temperature of a system causes a shift to absorb some of the added heat energy. A decrease in temperature causes a shift to replace some of the energy that has been removed.
  
  
• Volume (or pressure) change: An increase in volume (decrease in pressure) causes a shift toward the side with the larger total chemical amount of gaseous entities. A decrease in volume (increase in pressure) causes a shift toward the side with the smaller total chemical amount of gaseous entities.

Self-Check

SC 1. Complete “Practice” questions 2 and 3 on page 695 of the textbook.