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Q & A: thermodynamics and small systems

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Most recent answer: 07/14/2015
Q:
Why thermodynamics is not applicable for micro molecules?
- Imran (age 20)
India
A:

The basic laws of statistical mechanics are applicable to small or large systems. Some of the thermodynamic laws are just averaged versions of the statistical laws, with the average become very accurate only when enough parts are present.

Here's an example. In statistical mechanics one describes the entropy of a system of any size when some things about it are known, say the types of molecules, the volume they're in, and the energy they have. If, instead of knowing what the energy was, you knew what the temperature of their environment was, you'd get a  bigger entropy because they could have a little more or less energy than the average value. Thermodynamics treats those two entropies as equal. That works for big systems, where the fluctuations around the average aren't important.

Mike W.


(published on 07/14/2015)

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