Correct statement of 2nd law of thermodynamics?

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Discussion Overview

The discussion centers around the correct statement of the second law of thermodynamics, exploring various interpretations and formulations of the law. Participants examine different statements, their logical equivalence, and implications, as well as the relationship between entropy and energy in thermodynamic processes.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that in isolated systems, entropy never decreases and heat never spontaneously passes from colder to warmer bodies, suggesting these are foundational statements of the second law.
  • Others argue that these two statements are logically equivalent and that there are multiple equivalent formulations of the second law, with no single statement being more correct than another.
  • Some contributions propose that statements regarding total energy quality decreasing and energy dispersing are more descriptive and may be consequences of the second law rather than direct statements of it.
  • A participant inquires about a mathematical formulation of the second law, indicating interest in a more formal representation.
  • One participant discusses the concept of entropy in relation to energy quanta, suggesting that a cooling system may exhibit decreasing entropy due to a reduction in energy quanta, while also noting the increase in the reservoir's entropy.
  • Another participant responds to this by emphasizing the need to consider both the system and the reservoir, particularly in reversible and real processes, highlighting the complexity of entropy changes.

Areas of Agreement / Disagreement

Participants express differing views on the statements of the second law, with some asserting logical equivalence while others propose that certain statements are merely descriptive. The discussion remains unresolved regarding which formulations are most appropriate or accurate.

Contextual Notes

There are limitations in the discussion regarding assumptions about the definitions of entropy and energy quanta, as well as the implications of reversible versus irreversible processes. These aspects are not fully explored or resolved.

Karagoz
Thermodynamics is stated in different ways. E.g.
In isolated systems entropy never decreases
Heat never spontaneously pass from colder to warmer body
Total energy quality decreases in all processes.
Energy disperses

But what is it exactly? What is the correct description of the 2nd law of themodynamics?
 
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Karagoz said:
Thermodynamics is stated in different ways. E.g.
In isolated systems entropy never decreases
Heat never spontaneously pass from colder to warmer body
Total energy quality decreases in all processes.
Energy disperses

But what is it exactly? What is the correct description of the 2nd law of themodynamics?
Yes.
 
Karagoz said:
In isolated systems entropy never decreases
Heat never spontaneously pass from colder to warmer body

Those two statements are logically equivalent. (That is, if you assume either one as a premise you can show that the other follows as a consequence.)

They are each statements of the 2nd Law. There is no way to say that either one is more or less correct than the other. And there are several other logically equivalent statements that are also equally correct statements of the 2nd Law.

These, on the other hand, seem more descriptive. They are perhaps consequences of the 2nd Law? But I wouldn't refer to them as statements of the 2nd Law.

Total energy quality decreases in all processes.
Energy disperses
 
Would you like to see a mathematical statement of the 2nd Law of Thermodynamics?
 
Mister T said:
Those two statements are logically equivalent. (That is, if you assume either one as a premise you can show that the other follows as a consequence.)

They are each statements of the 2nd Law. There is no way to say that either one is more or less correct than the other. And there are several other logically equivalent statements that are also equally correct statements of the 2nd Law.

These, on the other hand, seem more descriptive. They are perhaps consequences of the 2nd Law? But I wouldn't refer to them as statements of the 2nd Law.

2nd law of Thermodynamics says that total entropy never decreases in a closed system (in the universe).

In this link entropy is explained as "nr of possible arrangements": https://aatishb.com/entropy/
If you take a quick look at the link, according to the link above, more energy quants in a body can have more nr. of possible arrangements. Less energy quants in a body can have less nr. of possible arrangements.
Then that means any system that's cooling down (e.g. hot coffee cooling down) has a decreasing entropy, because the systems' energy quants decreases?
 
Karagoz said:
decreasing entropy, because the systems' energy quants decreases?
... plus the "quants" increasing in the reservoir given up by the "coffee cooling." At least as much for a "reversible" process, zero net change, and for any "real process" occurring in less than infinite time, a greater than zero change.
 

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