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Theresa Julia Zielinski Monmouth University West Long Branch, NJ 07764-1898
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Cl2O4 in the Stratosphere
A Module from the Physical Chemistry On-Line Project1
George Long Indiana University of Pennsylvania Indiana, PA 15705-1090
David M. Whisnant*2 Department of Chemistry, Wofford College, Spartanburg, SC 29303; *
[email protected] Lisa Lever Department of Chemistry, University of South Carolina Spartanburg, Spartanburg, SC 29302 Jerry Howe Department of Chemistry, Converse College, Spartanburg, SC 29303
Physical chemistry is often perceived as one big collection of derivations with very little connection to reality. This is not really the case because mathematical models often can be applied to help us better understand real phenomena. An example is research on the physical chemistry of the atmosphere that led to the 1995 Nobel Prize in Chemistry for Sherwood Rowland, Mario Molina, and Paul Crutzen. Their pioneering calculations on the chemical mechanisms that affect the stratospheric ozone layer and subsequent work by several researchers have helped us realize that man-made chemicals can have serious effects on the earth’s atmosphere. The depletion of ozone in the stratosphere is caused chiefly by ozone reacting with chlorine and bromine from industrially manufactured gases. Several small chlorine oxide molecules are involved in the catalytic cycles that lead to the destruction of ozone. In this comprehensive project, students use computational chemistry to investigate a larger chlorine oxide, Cl2O4. Students start the project by reading a scenario and then follow a series of hyperlinks to develop, along with their colleagues, a better understanding of the implications of the presence of Cl2O4 in the atmosphere. Computational chemistry is introduced and employed to illuminate the role of chlorine oxides in stratospheric ozone depletion. The project includes extensive, embedded resources that allow students to begin by drawing Lewis structures, and conclude by conducting ab initio calculations to determine the molecular enthalpies of all the species in the reaction of dichlorine tetraoxide with ozone. Using the calculated enthalpies, they predict the reaction’s importance in the stratospheric oxygen cycle. Along the way, students learn some history, apply group theory to predict normal-mode behavior, learn to distinguish semi-empirical from ab initio methods, employ some simplifying assumptions about entropy changes in gas phase reactions, and conduct advanced molecular modeling cal-
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September 22, 2004 Antarctic Ozone Hole. This NASA image was obtained from their Web site: http://www.nasa.gov/vision/ earth/lookingatearth/ozone_hole_2004.html. A color version of the image appears on the cover of this issue.
culations. They directly apply the concepts they have learned in physical chemistry to answer a question relevant to their world. The zip file for this project contains the files needed for use of the project in a class intranet. The instructor notes provide an overview of the project. The assignment schedule and groups are the only files that must be edited every time the project is implemented. The calculations for the project have been completed using Spartan,3 HyperChem,4 and Gaussian software.5 Sample results are included in the collection of files. A small set of assessment questions provide the preliminary step for any faculty member wishing to determine the effectiveness of the module for student mastery of some concepts.
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Obtaining the Module
Available in the JCE LrnComOnline section of JCE Online is the zip file Cl2O4Project.zip. It contains the files needed for use of the module as well as instructor notes, an assignment schedule, group information, sample results, and a small set of assessment questions. In addition to the module files, Spartan, Gaussian, or HyperChem software is required. Notes 1. The Physical Chemistry On-Line project (http:// bluehawk.monmouth.edu/~tzielins/PCOLWEB/ChemOnLine, ac-
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cessed Nov 2004) has been supported by the National Science Foundation’s Division of Undergraduate Education, the Camille & Henry Dreyfus Foundation, the National Science Teachers Association, and the Foundation for Independent Higher Education. 2. At present David M. Whisnant is Vice-President for Technology at Wofford College. 3. Spartan is available from Wavefunction, Inc.; http:// www.wavefun.com (accessed Nov 2004). 4. HyperChem is available from Hypercube, Inc.; http:// www.hyper.com (accessed Nov 2004). 5. Gaussian is available from Gaussian, Inc.; http:// www.gaussian.com (accessed Nov 2004).
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