Entropy Decrease: Sample Phenomena Explained

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Discussion Overview

The discussion revolves around the concept of local entropy decrease within thermodynamic systems, particularly in relation to the Second Law of Thermodynamics. Participants explore whether entropy can decrease in a localized area as long as it is compensated by an increase elsewhere, and they seek examples of phenomena that illustrate this principle.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that entropy can decrease locally if the decrease is offset by an increase in the surrounding environment, citing examples like air conditioners.
  • Others argue that while local decreases in entropy can occur, they require work to be applied, and question the existence of spontaneous entropy decreases without external influence.
  • A participant mentions that biological processes often operate under this principle of local entropy decrease.
  • There is a contention regarding the necessity of work for entropy decrease, with one participant asserting that cooling a hot object results in a spontaneous decrease in its entropy without the need for work.
  • Another participant challenges the notion of spontaneous entropy decrease, suggesting that it is only observable under specific conditions, such as the origins of life.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which entropy can decrease locally. While some agree that local decreases are possible with compensatory increases elsewhere, others dispute the necessity of work and the spontaneity of such decreases, indicating an unresolved debate.

Contextual Notes

Participants reference the Second Law of Thermodynamics and its implications, but the discussion reveals varying interpretations of its application, particularly regarding spontaneous entropy changes and the role of work.

Domenicaccio
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Sorry but I suck at thermodynamics...

Can entropy decrease LOCALLY, provided that the decrease is compensated by an increase in the rest of the universe (or whatever isolated system we are in), so that the total change of entropy is positive?

Can you provide a sample phenomenon where this happens?
 
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Yes, entropy can decrease locally at the expense of increased entropy elsewhere. An everyday example is an air conditioner.
 
temporarily yes...
take a room filled with gas.
the density in any small given sample volume of the room will have varying number of molecules, thus varying randomess, or entropy.
However the overall entropy of the isolated system (here, room) will be constant.
 
Yes- nearly all of biology/biochemistry works using this principle.
 
D H said:
Yes, entropy can decrease locally at the expense of increased entropy elsewhere. An everyday example is an air conditioner.

How easily can you guarantee that the entropy of a certain subsytem (e.g. an amount of water in a container) will be decreased by COOLING it?

(Obviously, the refrigerator would cause an entropy increase somewhere else)
 
to decrease entropy you must apply work, this work will coase an increase of entropy somewhere else. But I do not think there is an example of entropy decreasing spontaneously, unles you go back to the beginning of life (for which we cannot say exactly what happened)
 
bilha nissenson said:
to decrease entropy you must apply work, this work will coase an increase of entropy somewhere else. But I do not think there is an example of entropy decreasing spontaneously, unles you go back to the beginning of life (for which we cannot say exactly what happened)

This is completely wrong. Whenever a hot object cools, its entropy decreases. No work is necessary. There is no problem with the entropy of an object or a system decreasing spontaneously. What the Second Law forbids is the tendency for the total entropy in the universe to decrease spontaneously.
 

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