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Entropy Is Simple, Qualitatively
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Abstract
Qualitatively, entropy is simple. What it is, why it is useful in understanding the behavior of macro systems or of molecular systems is easy to state: Entropy increase from a macro viewpoint is a measure of the dispersal of energy from localized to spread out at a temperature T. The conventional q in qrev/T is the energy dispersed to or from a substance or a system. On a molecular basis, entropy increase means that a system changes from having fewer accessible microstates to having a larger number of accessible microstates. Fundamentally based on statistical and quantum mechanics, this approach is superior to the non-fundamental "disorder" as a descriptor of entropy change.The foregoing in no way denies the subtlety or the difficulty presented by entropy in thermodynamics—to first-year students or to professionals. However, as an aid to beginners in their quantitative study of thermodynamics, the qualitative conclusions in this article give students the advantage of a clear bird’s-eye view of why entropy increases in a wide variety of basic cases: a substance going from 0 K to T, phase change, gas expansion, mixing of ideal gases or liquids, colligative effects, and the Gibbs equation.
Keywords (Audience):
High School / Introductory ChemistryKeywords (Subject):
ThermodynamicsCiting Articles
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This article has been cited by 13 ACS Journal articles (5 most recent appear below).
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Arnd H. JungermannJournal of Chemical Education2006 83 (11), 1686Entropy and the Shelf Model: A Quantum Physical Approach to a Physical Property
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- Received: August 03, 2009
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