1. Module 7

1.23. Page 3

Lesson 5

Module 7—Principles of Chemical Equilibrium

Try This
 
An Equilibrium Law

 

Purpose

 

To test various mathematical formulas to see if they can provide an equilibrium law, a general formula describing how to calculate an equilibrium constant is required.

 

TR 3. Read “Lab Exercise 15.A” on page 683 of the textbook. Complete an analysis by calculating an answer for each of the proposed formulas for an equilibrium law. Use the trials shown in “Table 6” on page 683. A suitable formula will produce the same value (a constant) from the data for all five trials.

 

TR 4. Which of the proposed formulas tested in “Lab Exercise 15.A” provides a “constant” for the data analyzed?

 

Summarize the results of your calculations in a table. Save a copy of your table in your course folder.

 

Discuss

 

Post your answer and the table you developed in TR 3 to the discussion area for your class. Use your classmates’ responses to check your skill in accurately completing the calculations and to see whether you can identify a similar relationship that could be used to calculate an equilibrium constant.


Earlier you were asked to consider the three important relationships that should be incorporated into a mathematical approach to calculating an equilibrium constant. To review, these were as follows:

  • The concentrations of each species in the system are important values.
  • The position of an equilibrium is determined by the relative proportions of products to reactants.
  • A balanced chemical equation describes the proportions of reactants and products involved in the system.

D 1. Comment on whether the proposed formula you identified in TR 4 also incorporates the three important relationships in an equilibrium described above.

 

Read

 

Completing the analysis of the data shown in “Lab Exercise 15.A” provides valuable insight into what an equilibrium needs to be. Read from page 684 to the end of the summary on page 686 of the textbook to learn more about the development of an equilibrium law and the equilibrium constant, Kc. Work through the “Communication examples” in this section.

 

Try This

 

Watch the simulation “The Meaning of the Equilibrium Constant.” You will need your username and password for the textbook. (Remember to ask your teacher if you do not have these.) Once logged in, click on each of the following links in order: Nelson Chemistry Alberta 20-30, Student Web Centre Access, Chapter 15 Equilibrium Systems, Section 15.1, Extensions, simulation (under the header “Extension: The Meaning of the Equilibrium Constant”). The information presented reinforces the information on page 685 in the textbook.

 

As you work with this simulation, note that you are able to manipulate the following variables:

  • value of Kc, the equilibrium constant
  • volume of the container
  • temperature of the system
  • number of spheres in the system

TR 5. As you view the simulation you will be able to see information that describes the numbers of each particle, the speed of particles in the container, the container size, and the concentration of particles of each type versus time. Which of these pieces of information would provide the greatest information about the equilibrium in the system?

 

TR 6. Prepare a table to record the changes you wish to observe while manipulating each of the variables listed in the bullet list. Record observations of how the equilibrium is affected by the changes you make.

 

You may wish to complete the self-scoring quiz that appears in the lower box of the animation window. Make note of answers you do not get correct. You may wish to verify your understanding using the textbook or other reference materials.

 

Save your work in your course folder.

 

Read

 

In some situations, the value for Kc can be used to determine the expected change in the concentration of substances, as equilibrium is established. In such a situation it is important to remember that the value you are required to solve for, is the change in concentration. You may wish to use the structure of an ICE table to help define your variables and relationships. This will help you complete the mathematical calculations.

 

Read “Predicting Final Equilibrium Concentrations” on pages 686–687 of the textbook. Work through “Sample problem 15.2” in the reading to see how these types of problems are solved.