The reversible processes conserve both the quantity (1LT) and quality of energy (2LT), where a process output is energy-wise equivalent to its input and vice versa in every way, quantity and quality-wise. Therefore, the reversible processes are all perfect and, equally and the most efficient, thus establishing the fundamental "Reversible Equivalency" concept, with the crucial consequence that if the Second Law of thermodynamics (2LT) could be somehow 'specially' violated, then, by the Reversible Equivalency extension, it would be violated in general.
“The Second Law of thermodynamics (2LT) can be challenged, but not violated — Entropy can be decreased locally [by transfer], but not destroyed at any space or time scales. […] The self-forced tendency of displacing nonequilibrium useful-energy towards equilibrium, with its irreversible dissipation to heat, generates entropy, the latter is conserved in ideal, reversible processes, and there is no way to self-create useful-energy from within equilibrium alone, i.e., no way to destroy entropy”.— [PFL, 2023], [http://2LT.MKostic.com] (accessed on 22 January 2024).
https://doi.org/10.3390/e25071106 (accessed on 17 January 2024):
Challenge Point A: “Entropy of an isolated, closed system (or universe) is always increasing” is a necessary but not sufficient condition of the Second Law of thermodynamics. Entropy cannot be destroyed (annihilated), locally or at a time, and “compensated” by generation elsewhere or later. It would be equivalent to allowing rivers to spontaneously flow uphill and compensate for it with a more downhill flow elsewhere or later, or to violate the 2LT in the Northern hemisphere this year and compensate for it in the Southern hemisphere or next year. Thermodynamic (macroscopic) entropy is generated everywhere and always, at any scale (where it could be defined) without exception, and it cannot be destroyed by any means at any scale. The impossibility of entropy reduction by destruction should not be confused with a local entropy decrease due to entropy outflow with heat [13,17,18,19,20,21,22].
Challenge Point B: Kelvin's 2LT definition, "A full [100%] conversion of the heat to the work is not possible in a cyclical process [Britannica et al.].", is true [weakly] but not exhaustive (not sufficient/complete): Namely, even a partial conversion of heat to work is not possible if higher than in the corresponding ideal Carnot cycle. Not only 100% of conversion is not possible, but also 75% would not be possible if, for example, heat at 1000K is converted to the work and the remaining 25% transferred to a 300K reservoir, since it is higher than the 70%=1-(300K/1000K) maximum possible conversion by Carnot cycle -- and it would result in violation of the Second Law of Thermodynamics (2LT) with impossible entropy destruction. Note, Clausius' 2LT definition: "A cyclic transformation whose only final result is to transfer heat from a body at a given temperature to a body at a higher temperature is impossible [Britannica et al.]."
NOTE: With negligible friction and without load, devices appear to move forever (PMM0) and some inventors and opportunists (mostly in the past) have believed and implied violation of the 1LT (PMM1), or nowadays, violation of more elusive 2LT (PMM2) while confirming validity of the 1LT and often validity of the “entropy law (no destruction of entropy”), as to validate their misplaced claims, but somehow perpetually getting work from the single thermal reservoir in equilibrium alone. The latter violation is a “contradiction impossibility” of validity of the “entropy law” (the two 2LT versions are equivalent as are all other versions) thus making such claims invalid.
PMM0: or PM: Perpetual-motion machine of the zeroth kind (or “Perpetual [free] motion” in short) that violates the irreversible dissipation or friction (impossibility of free perpetual motion without dissipative resistance).
PMM1: Perpetual-motion machine of the first kind that violates the 1LT (impossibility of creating energy from nowhere).
PMM2: Perpetual-motion machine of the second kind that violates the 2LT (impossibility of self-creating useful-energy or WP from within equilibrium).
PMM3: Perpetual-motion machine of the third kind that violates the 3LT (impossibility of converting all heat to work since absolute-0K temperature is unachievable).
PMM4: Perpetual-motion machine of the fourth kind that violates the 4LT (impossibility of evolution forever without decay, or similar: note that the 4LT is evolving in many forms and it is still to-be-defined!).
Second Law of Thermodynamics (2LT) - Holistic Reasoning and Generalization:
It Can Be Challenged, But It Cannot Be Violated! Entropy can be decreased, but cannot be destroyed!
The Second Law of thermodynamics is merely describing “natural-forcing and energy-displacement in specific direction, and not in the opposite direction, or spontaneous self-tendency of processes from nonequilibrium towards mutual equilibrium”, and impossibility otherwise.
See also Maxwell's Demon Demystified or http://Maxwell-Demon.MKostic.com
Entropy journal - Thermodynamics Section:
(2023): Reasoning and Logical Proofs of the Fundamental Laws: "No Hope" for the Challengers of the Second Law of Thermodynamics
(2022-23): Special Issue Exploring Fundamentals and Challenges of Heat, Entropy, and the Second Law of Thermodynamics: Honoring Professor Milivoje M. Kostic on the Occasion of His 70th Birthday
(2020): Topical Collection in Entropy: Foundations and Ubiquity of Classical Thermodynamics
(2020): Editorial: The Second Law and Entropy Misconceptions Demystified. Entropy 2020, 22, 648 * (OR)
Special Issues of Entropy journal edited by Prof. Kostic:
(2018): Nature of Heat and Entropy: Fundamentals and Applications for Diverse and Sustainable Future
(2016): Exploring the Second Law of Thermodynamics
(2013): Entropy and the Second Law of Thermodynamics
See also: Editorial * NIUToday * Dissecting 2ndLaw Challenges [https://goo.gl/cJ56jO] * Comments to Leff's "Key Points" (G)* PPT-XJTU2019
The 2nd Law is not about disorder and probability per se (or any other math or physics 'tools' per se used to describe it), but about spontaneous, forced-tendency (natural process-forcing displacement) of mass-energy redistribution in certain, irreversible direction (process driving force), from higher to lower energy-potential (mass-energy density in space). Spontaneity implies forced-directionality and in turn irreversibility. No spontaneous, irreversible process could ever be completely reversed or undone. For example, the driving force for life on Earth is the irreversible dissipation of energy from the Sun.
Challenges to the Second Law Challengers: The 'challengers' need to demonstrate and quantify destruction of entropy to challenge the universal validity of the Second Law. It has been reasoned and thus proven here that destruction of entropy, i.e., violation of the Second Law, is against the forced tendency of natural processes and thus impossible, leaving 'No Hope' for the challengers. After all, the 'Wishful Maxwell's Demon' could not be realized since 1867. [See also arXiv & Harvard and my Comments on Arrow of Time and Common Law of Physics]. After all, before 'the 2nd Law violation' claims are stated, the reliable criteria for the 2nd Law violation, including proper definition and evaluation of entropy, should be established based on full comprehension of the fundamental Laws.
It is hard to believe that a serious scientist nowadays, who truly comprehend the 2nd Law and its essence, would challenge it based on incomplete and elusive facts.
(Thermodynamics is subtle and elusive. Sometimes, highly accomplished scientists in their fields, do not fully comprehend the essence of the 2nd Law of thermodynamics)
*
The current frenzy about the 2nd Law violation (getting 'useful energy' from within equilibrium alone-PMM2) is in many ways similar to the prior frenzy about the 1st Law violation (getting 'energy' from nowhere-PMM1).
As the fundamental laws of nature and thermodynamics are expanded from simple systems in physics and chemistry, to different space and time scales and to much more complex systems in biology, life, and intelligent processes, there are more challenges to be comprehended and understood.
The perpetual, stationary quasi-equilibrium structures (with bounded non-uniform properties within gravity, electromagnetic or electro-chemical fields) are abundant in nature. As “field-charged bounded structures,” sometimes with elusive work-potential, they may provide limited, transient work only, but not perpetual work to violate the Second Law of thermodynamics, as some are misled to believe. For example, hydrostatic pressure distribution in a container, or adiabatic atmospheric-temperature distribution, or non-uniform distribution of other properties in a stationary equilibrium (like a heated adiabatic-container, compressed container, charged condenser, battery cell, fuel compound, etc.). We called the above a “structural equilibrium” (with non-uniform properties), as opposed to a simple 'ideal thermodynamic equilibrium' (with uniform properties) see Appendix.
