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Thermal Physics

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15 Jan 2012 21:59:44 IST

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Entropy: Ambiguity in statements.

Physics

Statement 1: Entropy is not a conversed quantity. It can only be created but can not be destroyed.
Statement 2: Entropy decreases with decrease in the temperature of an isolated system.

Which of the above is true and why is the other false.
PS: I am sure "statement 1" is correct. If that is case then 2 must be wrong. But general understanding tells us that as temperature decreases, KE of molecules decreases, and hence disorder in the system decreases. Please explain.

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Comments (6)

nageen

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15 Jan 2012 23:00:01 IST

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i dont think the statement 1 is right bcoz we know reactions where the entropy decreases...for example wen steam is converted into water in liquid state the entropy decreases

Arjun Virmani

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16 Jan 2012 12:31:28 IST

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Statement 1 is wrong!!

In simple words, Entropy is the measurement of randomness in a body or of a reaction, etc.

so if the randomness decreases, the entropy decreases.

as said from gas to liquid eg: steam to water or liquid to solid!!!

sirisha

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16 Jan 2012 17:27:59 IST

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WAT IS MEANT BY CONVERSED QUANTITY

Pawan B Joshi

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16 Jan 2012 21:58:34 IST

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Sorry. Its 'conserved' quantity. And @nageen & arjun: Well folks, sometimes intuitive ideas arnt correct. In short, common sense doesnt always do the trick. I too strongly feel you guys are correct, but we're all disagreeing with HC VERMA..!

arna ghosh

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17 Jan 2012 19:02:08 IST

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guys......we are missing a small term- "the universe"the entropy of the system can decrease if it loses heat.But then the surroundings gain heat at a lower temp.say Q1 is temp. of system and Q2 the temperature of surrounding. (Q1>Q2)say H heat is transfered.....we see that net entropy change= H{(1/Q2)-(1/Q1)}since 1/Q1<1/Q2,net entropy change is positive...Hence entropy increases. :-D

Pawan B Joshi

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18 Jan 2012 22:17:40 IST

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Jolly good. Thanks.

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