- #1
asdf1
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Why is the definition different in physics and chemistry for the 2nd law of thermodynamics?
Why Do Physics and Chemistry Define the 2nd Law of Thermodynamics Differently?
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Homework Help Overview
The discussion revolves around the differing definitions of the second law of thermodynamics in physics and chemistry, focusing on how entropy is interpreted and applied in each field.
Discussion Character
- Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants explore the reasons behind the different applications of entropy in chemistry and physics, noting that chemists focus on energy release in reactions while physicists emphasize heat flow and work. Questions about the Kelvin-Planck and Thomson statements of the second law are also raised.
Discussion Status
The discussion is ongoing, with participants sharing insights and humorous takes on the complexity of entropy definitions. Some guidance on the differences in focus between the two fields has been provided, but no consensus has been reached regarding a unified definition.
Contextual Notes
Participants express a desire for a simpler definition of entropy, reflecting on the challenges and nuances in understanding the second law of thermodynamics.
- #2
Andrew Mason
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Entropy is defined the same way. dS=dQ/T. But it is used in different ways.asdf1 said:
Chemists are concerned with the release of energy in a reaction. The entropy difference between two states tells the chemist about the direction of the reaction and the magnitude of heat energy that is releaseable. The physicist is concerned with heat flow between reservoirs and the amount of work required to achieve such flow (or obtainable as a result of such flow).
AM
- #3
asdf1
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is the kelvin-planck statement the same as the thomsen statement?
- #4
Andrew Mason
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They are not the same but they both express the second law. (Wm. Thomson was Lord Kelvin).asdf1 said:
Thomson originally observed that “it is impossible by means of inanimate material agency to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects” . The Kelvin-Planck statement of the second law is: "It is impossible to obtain a process that, operating in cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work".
So it was not just physics students who struggled with the definition of entropy.
AM
- #5
asdf1
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haha...thanks~
it'd be nice if there were just one simple definition of entropy...
it'd be nice if there were just one simple definition of entropy...
- #6
Danger
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The way that I saw it described about 35 years ago was:asdf1 said:
1) No matter how hard you try, the best that you can do is break even.
2) Breaking even can only be achieved at absolute zero.
3) Absolute zero is impossible to attain.
4) Give up and go make a sandwich.
Of course, that's pretty silly... but I like it.
- #7
asdf1
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lol~
(4) is funny...
(4) is funny...
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