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Entropy clausius 
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#1
Feb1913, 05:57 PM

P: 71

Hi,I m just beginner in physics,but actually I don need exact expression of physical laws in math language.I know,math is language of physics but still.....
So,I m looking for answer to my questions about origin of Clausius s entropy. I this article: http://www.panspermia.org/seconlaw.htm is written,that Clausius decided define entropy,because q/T was constant.And my question is:Why only constant ratios are some physical properties?What does it mean to be constant property in nature.It is quite bit physical,but for my starting point,I just want to know,what is physical view,how physics works.... So,if you can,try exaplain me,why constant ratios can be assumed to be property and why not all constant ratios are physical quantity.Why Clausius decided to define ratio q/T to be entropy? THanks a lot 


#2
Feb1913, 06:26 PM

Sci Advisor
P: 8,544

The key achievement is that entropy defined by Clausius dS=dQ_{rev}/T is a state property.
In general, you can imagine that to predict what is going to happen next, you need to know everything that happened before. However, the special property of a state variable is that to make a prediction, you just need to know it at one moment in time. (That's the rough idea.) An example of something that isn't a state property is the work done on an object  that depends on the path through which you moved an object. Mathematically, he discovered what is called an "integrating factor". http://en.wikipedia.org/wiki/Integrating_factor 


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