Information • Textbooks • Media • Resources edited by
Jon L. Holmes Nancy S. Gettys University of Wisconsin–Madison Madison, WI 53706
G and S
W
Issue 9802W for Windows Ian McNaught University of Sydney, School of Chemistry, Sydney, New South Wales 2006, Australia
G and S is designed to show Gibbs energy and entropy as a function of extent of reaction. It can be used to determine equilibrium compositions and changes in Gibbs energy and entropy for reactions, and to invite the exploration of differences and relationships between various thermodynamic properties. Changes in the system, surroundings, and universe are all available to show different ways in which the second law of thermodynamics can be used to determine the direction of spontaneous change and the position of equilibrium. It permits quantitative tests of qualitative predictions of the effect on equilibrium position following a change in the conditions. G and S can be used as a lecture demonstration or as a dry lab for students to explore the interrelationship between Gibbs energy, entropy, and equilibrium. An extensive exercise illustrating many uses of the program is included.
This exercise uses G and S to illustrate the following: 1. Determination of equilibrium amounts by minimizing the Gibbs energy. 2. Equality of Kp obtained from these equilibrium amounts and from ∆G° = –RT lnKp. 3. Determination of equilibrium amounts by maximizing the entropy of the universe. 4. Demonstration that the maximum for S(universe) occurs at a different position from the maximum for S(system) emphasizing the primacy of S(universe). 5. Recognition of the relationship between the sign of ∆H for the spontaneous process and the sign of ∆S(surroundings). 6. Numerical confirmation of the results ∆G = ∆H(sys) – T∆S(sys) and ∆G = – T∆S(universe). 7. Confirmation (or otherwise) of qualitative predictions based on Le Châtelier’s principle of the effect on the position of equilibrium of changing reaction conditions. 8. How to choose mole ratios of reactants so as to maximize yield of product or use of a particular reactant.
Plots from G and S
How To Use G and S G and S is intended for use by physical chemistry students. It could be used as a lecture-demonstration tool in class, or by students on their own. Hardware and Software Requirements Hardware and software requirements for G and S are listed in Table 1. Table 1. Hardware and Software Required for G and S Computer
CPU
RAM
Drives
Free Disk Space
Windows Compatible
80386 or higher
≥ 8 MB
Hard Drive, High-density (1.44MB) floppy drive
1 MB
Graphics ≥ 256 colors, 640 × 480
Operating System
Other Software
Windows 3.1 or Windows 95
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Ordering and Information
Editor’s Note JCE Software now publishes software programs individually as they are ready for publication, rather than bundling two or more programs into issues as we have previously. Doing so allows us to publish software in a more timely fashion, because
Journal of Chemical Education Software or JCE Software is a publication of the Journal of Chemical Education. An Order Form inserted in this issue provides prices and other ordering information. If this card is not available or if you need additional
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we will not have to wait for the technical difficulties of all programs to be solved before we can publish any of them. Publishing programs separately will make it easier for you to select and
JChemEd.chem.wisc.edu • Vol. 75 No. 5 May 1998 • Journal of Chemical Education
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