Entropy Is Simple, Qualitatively

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 q rev/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.

Good Use of a ‘Bad’ Metaphor

“…& The disorder metaphor emphasises spatial configuration of the constituent particles of a system, but tends to neglect the role of energy (Lambert 2002b(Lambert , 2007Alonso and Finn 1995;Brosseau and Viard 1992). & The messy room analogy and other examples, such as a particular poker hand, give a single snapshot view, rather than showing the large number of microstates, i.e.…”

“…However, I would like to counter these views with some arguments in its favour. Lambert (2002b) argued that 'entropy is simple, qualitatively', if it is explained macroscopically as a measure of the dispersal of energy and microscopically as the number of microstates of a system, and Leff (2012) set out 'removing the mystery of entropy' by relating it to the spreading of energy. Similarly, Ben-Naim (2007) proclaimed 'entropy demystified' and promised to reduce it to 'plain common sense' by interpreting it as identical to information.…”

Entropy, Its Language, and Interpretation

“…In 1996, the spreading metaphor was used to introduce and motivate the development of thermodynamics pedagogically [19]. In 2002, Lambert [9,20] argued in favor of energy-based language to replace the inadequate metaphor of disorder in chemistry textbooks. The present paper is intended to extend the discussion of the spreading metaphor for a wider audience of research scientists.…”

Entropy and Constraint of Motion

“…I would like to make several observations supplementing and supporting the article by Frank Lambert on entropy as energy dissipation, since this is an approach that I have also used for many years when teaching a qualitative version of the entropy concept to students of general and introductory inorganic chemistry (1).…”