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Disorder - A Cracked Crutch for Supporting Entropy Discussions
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Abstract
To aid students in visualizing an increase in entropy, many elementary chemistry texts use artists' before-and-after drawings of groups of "orderly" molecules that become "disorderly". This seems to be a useful visual support, but it can be so misleading as actually to be a failure-prone crutch. Ten examples illustrate the problem.Entropy is not disorder, not a measure of chaos, not a driving force. Energy's diffusion or dispersal to more microstates is the driving force in chemistry. Entropy is the measure or index of that dispersal. In thermodynamics, the entropy of a substance increases when it is warmed because more thermal energy has been dispersed within it from the warmer surroundings. In contrast, when ideal gases or liquids are allowed to expand or to mix in a larger volume, the entropy increase is due to a greater dispersion of their original unchanged thermal energy. From a molecular viewpoint all such entropy increases involve the dispersal of energy over a greater number, or a more readily accessible set, of microstates. Frequently misleading, order-disorder as a description of entropy change is also an anachronism. It should be replaced by describing entropy change as energy dispersal--from a molecular viewpoint, by changes in molecular motions and occupancy of microstates.
Keywords (Audience):
High School / Introductory ChemistryKeywords (Pedagogy):
Misconceptions / Discrepant EventsKeywords (Subject):
ThermodynamicsCiting Articles
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This article has been cited by 23 ACS Journal articles (5 most recent appear below).
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Evguenii I. KozliakJournal of Chemical Education2009 86 (9), 1063Overcoming Misconceptions about Configurational Entropy in Condensed Phases
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- Received: August 03, 2009
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