JCE Online Journal of Chemical Education
 | Subscriptions  | Software Orders  | Support  | Contributors  | Advertisers  | 

JCE Print
   Current Issue
 Previous Issues
 Supplements
 Search JCE Index

JCE Digital Library
   DigiDemos
 QBank
 SymMath
 WebWare

JCE Software
   Latest Releases
 Software & Video
 Downloads
 Support

Only@JCE Online
   JCE Online Store
 JCE HS CLIC
 JCE Discussion Forums
   Biographical Snapshots
 ChemEd Resource Shelf
 Featured Molecules
 Hal's Picks
 Project Chemlab
 Reviewed WWW Sites
 "Web-Ed" Articles

About JCE
   Features
 Publications
 Operations
 Outreach
 Contact Us


  Home > JCE Print > Journal of Chemical Education > Issues > 2003  > December  >
In the Classroom
Campbell's Rule for Estimating Entropy Changes in Gas-Producing and Gas-Consuming Reactions and Related Generalizations about Entropies and Enthalpies
Norman C. Craig
Department of Chemistry, Oberlin College, Oberlin, OH 44074-1083
Cover
December 2003
Vol. 80 No. 12
p. 1432
Abstract
Learning how to estimate thermodynamic quantities and how to use estimates extends the usefulness of thermodynamic analyses of chemical reactions. Estimating helps chemists understand why chemical reactions occur and why the outcomes change with temperature. A new generalization with the suggested name of Campbell's rule, where ΔrS° ≈ 140 J/(K mol rxn) per net mole of gas produced in a reaction, is introduced. This rule enables estimating entropies of reaction from the net change in moles of gas whenever the formation or combination of aqueous ions is not involved. A number of patterns in molar entropies are identified. These patterns are the basis for making good estimates of molar entropies of unknown or transient species from entropies of known species of the same phase, same bond type, same shape, similar composition, and similar mass. For several other types of processes, including reactions involving ions, the sign of ΔrS° is considered. For molar enthalpies and enthalpies of reaction we have fewer patterns than for entropies on which to build. The principal exceptions are recognizing the patterns in bond dissociation enthalpies and estimating enthalpies of reaction for gas phase processes. A simple scheme for estimating enthalpies of reaction for the gas phase is described.

See Letter re: this Article.
More Information
*  Citation
 Craig, Norman C. J. Chem. Educ. 2003 80 1432.
*  Keywords
 Gases; General Chemistry; Physical Chemistry; Teaching / Learning Aids; Thermodynamics
*  History
 Created:
Last Updated:		 October 31, 2003
February 28, 2005
Link to Letter added (October 2004)
<< Previous Article Table of Contents Next Article >>
  Home > JCE Print > Journal of Chemical Education > Issues > 2003 > December > Page 1432


Subscriptions
 Subscription Info
 Order Forms

JCE HS CLIC

Our Secondary School editors work hard to distill all the JCE materials to produce a fraction of particular interest to high school teachers. We call it CLIC.
 JCE HS CLIC

Contributions Welcome
JCE welcomes your submission
 Contributors' Corner

Advertisers
In recent years we have worked hard to better match our advertisers with our readers. When shopping for chemistry education materials, visit our advertisers' WWW sites first.
 Recent Advertisers

Be An Ambassador
Take JCE along on your outreach missions. Copies of the Journal, guest access to JCE Online, our publications catalog, and more are available for your participants.
 Outreach with JCE

Comments to
jceonline@chem.wisc.edu		 Copyright © Division of Chemical Education, Inc., American Chemical Society.
All rights reserved.