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Chapter 15 Equilibrium Systems

Section 15.1   Explaining Equilibrium Systems

Web Activity: Establishing Equilibrium (page 10)

This SIR Dynamic simulation illustrates the establishment of a simple dynamic equilibrium by showing how entities change (react) over time, beginning from an initial condition. Even though this simulation is very simplified, it has the great advantage of showing clearly and progressively the dynamic molecular change process.

[Use SIR Dynamic - on SIRs CD-ROM]

•  Start the SIRs program and, on menu screen, click on "SIR Dynamic."

•  The general instructions provide more detail than you are required to know. Pay particular attention to the first and third paragraphs. Click anywhere to proceed.

Part 1 - Different Starting Amounts

In this simulation you will investigate a simple reversible reaction, R D P , as it progresses from different initial amounts to the final equilibrium amounts.

1. Set up a table to record initial and final amounts of both R and P.
2. Record the initial amounts of R and P (top-right box).
3. Click "Load Reactor" along the bottom of the screen and then click, "Start the Reaction."
4. While the simulation is running, focus on a few molecules in the reactor and notice the changes occurring to individual molecules.
5. Once the simulation stops, record the final equilibrium amounts of R and P .
6. Use the mouse buttons in the top-right box to change the initial amounts to 30% R and 70% P and repeat steps 3 to 6.
7. Repeat step 6 using 0% R and 100% P and any other combination you wish to try.
8. Compare final equilibrium amounts for all combinations of initial amounts.

Part 2 - Different Values of K

In this simulation you will investigate two simple reversible reactions, R D P , with different equilibrium constants, K .

1. Reset amounts to 100% R and 0% P . Note that K = 1.50.
2. Click "Load Reactor" and then "Start the Reaction."
3. When the simulation is finished, click "Show Previous Plot" along bottom of screen.
4. Use the mouse buttons to change to K = 20.0 at the top of screen. (This would imply that we are changing the nature of the reactants and products.)
5. Run the simulation by clicking "Load Reactor" and then "Start the Reaction."
6. When the simulation is finished, compare the final amounts of R and P for the two equilibrium reactants. Notice the effect of the value of K on the final amounts at equilibrium.

Part 3 - Time to Reach Equilibrium

In this simulation you will change the time required to reach equilibrium of a simple reversible reaction, R D P by altering the activation energy (i.e., using a catalyst).

1. Restart the program to return to the default values.
2. In the 2 nd box at the top of the screen, "Dynamic Representation," click the second choice, " D G and E a ". Ignore the value of D G and notice that the activation energy is set to "small."
3. Run the simulation in the usual way.
4. When the simulation is finished, click "Show Previous Plot" along bottom of screen.
5. Change the E a by clicking on "small" until it changes to "medium".
6. Run the simulation and compare the final amounts at equilibrium and the time required to reach equilibrium for both systems.  

Web Activity: Canadian Achievers ¾ Paul Kebarle (page 15)

Paul Kebarle pioneered the measurements of gas-phase ion - molecule equilibria. Kebarle's findings, now significantly expanded by other workers, constitute a central data base that is of fundamental importance in many diverse fields of scientific research.

1.   What fundamental data did Kebarle and his co-workers obtain from their research?

2.   List three fields of research that have been aided by Kebarle's work.

Science.ca

This site provides profiles of many Canadian scientists; it also provides links to their personal Web pages.

Web Activity: Equilibrium Calculation (page 20)

This SIR K simulation calculates equilibrium concentration values for a variety of reactions, using your data input, and showing results as an ICE table.

[Use SIR K -- on SIRs CD-ROM]

•  Start the SIRs program and on menu screen, find the section titled Reactions and Equilibrium and click on SIR K .

•  The next screen provides some background and parameters for this program. Click anywhere to proceed.

•  In this simulation you will explore the calculation of final equilibrium concentrations using reaction (ICE) tables.

1. Click on the New Reaction box along the bottom of the screen.
2. Choose reaction #7 by double-clicking on it. You should now see the start of the reaction table with the chemical reaction equation entered.
3. Click anywhere in the Equilibrium Constant box and use the pop-up calculator to enter 4.20 (followed by the enter key, ¿ ).
4. The starting concentrations of any reactant and product can be changed by clicking on its value and using the pop-up calculator to enter a new value. Use this procedure to set the initial value of each reactant to 4.00 mol/L and leave the products at 0.00.
5. Click the Solve box along the bottom of the screen. Compare the changes in concentration and the final equilibrium concentration to the values given in your textbook for Sample Problem 15.2.
6. Repeat steps 4 and 5 using a variety of values for the starting amounts of reactants and products.
• Describe the pattern in the values for the changes in concentration. Why does this pattern occur?
• Is there a pattern in the final equilibrium concentrations? Discuss briefly.
7. Click on the New Reaction box along the bottom of the screen.
8. Choose reaction #8 by double-clicking on it.
9. Set the equilibrium constant to 0.065 and the starting amount of ammonia to 2.00.
• Using the balanced chemical equation, predict the changes in concentration in terms of +/- x.
10. Click Solve .
• Convert the changes in concentration to a simple, whole-number ratio.
• Evaluate your prediction.
11. Click on the New Reaction box and select reaction #6.
12. Enter 115 for the equilibrium constant and 0.200 mol/L for each reactant.
13. Set up an ICE table on paper showing the values in terms of x and then solve for all the unknown values.
14. Click Solve and check your answers using the values provided by the program.

    Extension

15. Choose other reactions to practice equilibrium calculations using ICE tables. Note that some reactions will be quadratics or higher polynomials but the program will always calculate the results.

Section 15.1 Questions (page 21)

Question 12

In a very long-term sense, Earth may be considered a closed system. One equilibrium system of concern to scientists is the same one involved in carbonation of soft drinks, on a vastly larger scale. Scientists believe that over time, the carbon dioxide gas in the atmosphere should be in equilibrium with carbon dioxide dissolved in the oceans. They also know that the concentration of CO 2 (g) in the atmosphere has been increased significantly (by about 20%) in the last century, which, they believe, is mostly due to the burning of fossil fuels. Concerns about the consequences of global warming make it imperative that scientists improve their theories about the various cycles, processes, and equilibria involving this "greenhouse" gas. Research and summarize currently accepted theory about carbon dioxide dissolved in the oceans, and list some other cycles and systems involving reaction or production of CO 2 (g).

Faster Carbon Dioxide Emissions will Overwhelm Capacity of Land and Ocean to Absorb Carbon

This illustrated article from the UC Berkley News described how computer modelling allows scientists to process data and draw some rather alarming conclusions.

Ocean Acidification Due to Increasing Atmospheric Carbon Dioxide

The Royal Society published this fairly lengthy paper in 2005. There is a section on biological impacts.

AOML Climate - Chemical Processes

The Atlantic Oceanographic and Meteorological Laboratory has done considerable research into the state of the oceans. Click on Chapter 3 to read, specifically, about the change in carbon dioxide content.

Section 15.2   Qualitative Change in Equilibrium Systems

Biology Connection: O 2 and CO 2 Transport (page 25)

Many biological processes depend on equilibria. The transport of oxygen around the body is just one of them. Another is the transportation of carbon dioxide, which depends on the CO 2 Û H 2 CO 3 equilibrium system. In the tissues of the body where carbon dioxide is produced, the equilibrium shifts so that more carbonic acid is formed. In the lungs, the shift is in the reverse direction, as carbon dioxide is released to an open system. You are likely to discover other examples of equilibria if you look through a biology textbook.

[Link to come.]

[Link to pdf of pages from Nelson Biology Alberta 20-30 - to come.]

Chemical Process Engineer (page 25)

What role do Chemical Engineers play in designing systems and sequences of reactions for industrial production of chemicals? Research the education requirements, job prospects, and work assignments of people in this profession.

National Occupational Classification: 2134 Chemical Engineer

Human Resources and Skills Development Canada's Web site provides much information about various careers within the larger category of "chemical engineer," one of which is "chemical process control engineer."

Campus Starter: Chemical Process Engineer

This web page describes the career, and enables you to search by province for schools that provide the necessary courses.

Case Study: Urea Production in Alberta (pages 28-29)

Question 1

Research Friedrich Wöhler's classic experiment of 1828. Write the balanced equation for the reaction he performed.

Wöhler's Synthesis

Wikipedia explains the series of reactions that results in the production of urea.

Wöhler's Letter of Discovery

This translation of W ö hler's letter to Berzelius, describing his famous reaction, shows his delight and excitement at his discovery. Berzelius' response is equally lighthearted.

Organic Chemistry

MSN's introduction to organic chemistry outlines Wöhler's initial reaction.

Question 4

Find out how much urea is produced annually in Alberta , where it is produced, and its current price per tonne. Assemble your findings into an attractive presentation.

Agrium

One of Alberta 's major producers of urea outlines the industrial process and the quantities produced.

Fertilizer Production Capacity Data ¾ Canada

The Canadian Fertilizer Institute produced this document outlining Canada 's production capacity for various fertilizers in 1999.

Greenhouse Gas Emissions and the Canadian Fertilizer Industry

This document, produced by Canada 's National Climate Change Process (NCCP), provides statistics on Canada 's production of ammonia and urea. The statistics for urea production, by facility, are clearly shown in a pie chart.

Section 15.2 Questions (page 31)

Question 8

In a deep lake or in the ocean, the pressure that a human considers "normal" has doubled by the time a diver reaches a depth of 10 m, and increases by about one atmosphere for every extra 10 m, to a maximum of about 100 MPa at the deepest points in Earth's oceans. This fact is of major concern to SCUBA divers for several reasons. Pressure inside a SCUBA diver's lungs must constantly be adjusted to equal outside water pressure, otherwise the lungs could collapse upon diving, and could explode upon rising. In fact, the development of the pressure regulator by Jacques Cousteau was the technology that made SCUBA diving possible.

The gases in a diver's lungs are dissolved to some extent in the blood that passes through. Pressure changes can change several solubility equilibria, with some serious effects. Research the gases dissolved in human blood, and what equilibrium shifts cause the diving conditions called nitrogen narcosis, and the "bends."

Decompression Sickness

Wikipedia has an extensive description of the sickness, its causes, and its treatment.

The Bends - Decompression Syndromes

E-Medicine's web page overview links to more details. (See right-hand column.)

Chapter 15 Review (pages 37-41)

Question 38

A halogen light bulb contains a tungsten (wolfram) filament, W(s), in a mixed atmosphere of a noble gas and a halogen.

Find out the role of temperature in the operation of a halogen lamp. For example, how is it possible for a halogen lamp to operate with the filament at 2700 °C when the tungsten normally would not last very long at this high temperature? Why is such a high temperature desirable?

The Halogen Lamp

Wikipedia describes how a halogen lamp operates, along with its pros and cons.

How Does a Halogen Light Bulb Work?

The "How Stuff Works" site has the answer to just about everything, including why a tungsten filament lasts a surprisingly long time.

Tungsten-Halogen Lamps

Sylvania , a well-established manufacturer of light fixtures, provides a simple description of how a halogen lamp operates.

Question 39

When the Olympic Games were held in Mexico in 1968, many athletes arrived early to train in the higher altitude (2.3 km) and lower atmospheric pressure of Mexico City . Exertion at high altitudes, for people who are not acclimatized, may make them dizzy or "lightheaded" from lack of oxygen. Use the theory of dynamic equilibrium and Le Châtelier's principle to explain this observation. How are people who normally live at high altitudes physiologically adapted to their reduced-pressure environment?

Adapting to High Altitude

This web page describes very clearly why newcomers to high altitudes cannot, initially, perform as well as they could at their normal altitudes.

The author also describes some evolutionary "strategies" that have enabled people to live and work at high altitudes for hundreds of generation.

Hemoglobin Levels in a Himalayan High Altitude Population

This abstract of a journal article indicates that populations of people living in different parts of the world may have evolved differently to their low-oxygen environment.

Question 44

Work within a group to research, assemble, and present a more complete and accurate summary of the operation of a typical Alberta industrial amine "scrubber" system. Emphasize the role of chemical equilibrium in this reaction system. Include information on applications of this process throughout Alberta . Your presentation should include use of the best features of any available word processing or slideshow software.

Wikpedia: Scrubber

Although not specific to amine scrubbing, this page describes different types of scrubbing and gives a short, general outline of how scrubbing works.

Canadian Clean Power Corporation

This file, TransAlta, Addressing Climate Change; Innovative Strategies for Alberta's Industry, on p. 20, includes a schematic showing "Flue Gas Amine Scrubbing."

Amine Gas Sweetening

NATCO Group's Web site describes the process of removing hydrogen sulfide (as well as other contaminants) from natural gas. NATCO has a manufacturing facility in Calgary , AB.