1. Module 7

1.27. Page 2

Lesson 6

Module 7—Principles of Chemical Equilibrium

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Try This
 
Demonstration of Equilibrium Shifts

 

View the virtual investigation “Demonstration of Equilibrium Shifts.”

 

Analysis

 

TR 1. For each of Tubes 2–5, indicate which substance, Co(H2O)62+ or CoCl42–, increases in concentration as a result of the manipulation performed on the tube during the demonstration.

 

TR 2. Suggest an explanation for the colour changes you observe.

 

Save a record of your observations and answers in your course folder. Throughout this lesson you will review your observations and consolidate your understanding of the principles introduced and developed throughout Lesson 6.

 

Read

 

In the demonstration you just completed, you saw that changing the conditions for a chemical system equilibrium causes a change to the equilibrium. In the demonstration, a colour change was distinct evidence that a shift in the position of an equilibrium had occurred. In your analysis of the observation, you were asked to identify which coloured species, Co(H2O)62+ or CoCl42, increased in concentration as a result of the change in conditions on that system.

 

How can the concentration of one of these substances change? Read pages 691–693 in the textbook to begin to address this question.

 

Le Châtelier’s principle describes a response by a chemical system at equilibrium that has been disturbed. This principle states that when a chemical equilibrium is disturbed, the system seems to respond in the direction that opposes the change (consumes or counteracts the stress). This principle allows you to predict the direction of the shift in the equilibrium.

 

Discuss

 

In the virtual investigation “Demonstration of Equilibrium Shifts,” you observed the effect of changing the concentration and temperature on the system being studied. Can you explain the colour change you observed in each of the tubes tested using Le Châtelier’s principle?

 

D 1. Retrieve your observations and answers to TR 1 and TR 2. Review the changes that occurred in each tube, and write an explanation for the change observed that demonstrates an understanding of Le Châtelier’s principle. Make sure your explanation for the change that occurred in each tube explicitly identifies the following points:

  • the “stress” placed on the system
  • which reaction, the forward or the reverse, is favoured to respond to the stress
  • how favouring the forward or reverse reaction serves to counteract the stress
  • the direction of the equilibrium shift

Once you have completed your answers, post them to the discussion area for your class. Review the postings of at least two other students. Provide feedback to the students to help them make their responses more clear and accurate, and to help them ensure they have addressed the aspects listed above.

 

Revise your response based on the textbook readings and any feedback you receive, and save your revised response in your course folder.