Comment on ‘A note on heat reservoirs and the like’

In a recent article in this journal, Brown and Singh present the results of an extensive in-class survey of student difficulties with the second law of thermodynamics. Here, we discuss in detail some issues identified by them in an attempt to resolve some of the problems. We do this by making clear the distinction between the ‘system entropy’, ‘reservoir entropy’, ‘total entropy’, and the ‘entropy of the universe’. We identify, without ambiguity, which quasistatic processes are ‘internally reversible’, which are ‘totally reversible’, and which are ‘irreversible’. We discuss the meaning of quasistatic processes represented by curves in the PV plane. We show that the process P=P(V) that takes an ideal gas from initial state (P_A V_A) to final state (P_B V_B) always takes the gas away from the adiabat PV^γ=P_A V_A^γ. We establish the increasing (total) entropy principle as the quantitative expression of the second law of thermodynamics. This establishes the fundamental role of the total entropy in macroscopic thermodynamics. Expressing the increasing (total) entropy principle in the form 〖(T〗_res-T_gas)d(PV^γ)>0 reveals which processes are allowed, which are not, and which points in the PV plane are accessible from a given initial state. Students can now observe the limitations on individual processes mandated by the second law. Such second law analysis is suitable for the introductory physics course.

“…We point out that failing to label the temperatures properly can lead to misleading, even incorrect, conclusions [9].…”

Section: The Increasing (Total) Entropy Principle: Irreversible Proce...mentioning

confidence: 93%

An ideal gas and the increasing (total) entropy principle: what is allowed in the PV plane and what is not

Marcella¹

2022

“…We then went on to define the process in a system, omitting the environment with which it is interacting, and extended our analysis to constant pressure reservoirs. In a recent comment [2], Anacleto and Ferreira claim that our treatment is incorrect because of an unsound interpretation of the Clausius relation and because we have not have been aware that a thermodynamic process is a system-surrounding interaction. In what follows we show that their criticisms are based on erroneous or irrelevant reasoning.…”

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confidence: 87%

“…There is more to say than by definition 'D = -S Q T e e together with the imposition that T e be constant constitute the definition of heat reservoir' [2]. Largeness itself is the ultimate responsible for both defining properties.…”

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confidence: 99%

“…There is no incoherence whatsoever in describing a process from the point of view of the particular systems involved alone. Nor does this approach imply that 'virtually every process would be reversible' [2]. Because it is not always possible to find two different environments that bring about the same change of state of a system by providing it with the same amount of energy, of the same kind under the same conditions, and that in turn change the character of the process as an isolated system.…”

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confidence: 99%

“…Finally, it is interesting that Anacleto and Ferreira have committed the error we criticised in the introduction of our article: sadly, all too often definitions are not physically motivated. There is more to say than by definition 'D = -S Q T e e together with the imposition that T e be constant constitute the definition of heat reservoir' [2]. Largeness itself is the ultimate responsible for both defining properties.…”

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confidence: 99%

See 2 more Smart Citations

Reply to Comment on ‘A note on heat reservoirs and the like’

Santos

López-Lacomba

2017

Comment on ‘Equivalence of the Kelvin–Planck statement of the second law and the principle of entropy increase’

Anacleto

2018

Self Cite

This comment addresses the paper by Sarasua and Abal (2016 Eur. J. Phys. 37 055103). Driven by an incorrect interpretation of the Clausius relation, those authors demonstrated the equivalence of the Kelvin–Planck statement of the second law and the principle of entropy increase. In addition to the necessary clarification of the Clausius relation, we propose an improved version of the demonstration made in the aforementioned paper, since the one carried out therein is restrictive. Our aim is to clarify issues that, being didactically and pedagogically relevant, are also subtle.