Meaning of formula from statistical physics

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SUMMARY

The formula discussed, S = -k∑_r{p_r ln p_r}, represents the entropy (S) in statistical physics, where k is the Boltzmann constant and p_r denotes the probabilities of various microscopic states. This equation illustrates that for each macroscopic equilibrium state, there exists a multitude of corresponding microscopic configurations, emphasizing that entropy increases with molecular randomness. The relationship between entropy and thermodynamic probability is further clarified by the Boltzmann relation, S = k ln(p), which indicates that higher uncertainty in molecular states leads to increased entropy.

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  • Understanding of statistical physics concepts
  • Familiarity with the Boltzmann constant (k)
  • Knowledge of probability mass functions
  • Basic grasp of thermodynamic principles
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broegger
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Hi.

Can anyone explain the meaning of this formula from statistical physics to me:

S = -k\sum_r{p_r\ln p_r}​

Ok, I know that S is the entropy, the p's are probabilities of some sort - but somehow this is not satisfactory :-)
 
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What this formula tells you is that for each state of macroscopic equilibrium there corresponds a large number of possible microscopic states or molecular configurations. The entropy, s, of a system is related to the total number of possible microscopic states of that system, called the thermodynamic probability p, by the Boltzmann relation:

S= k*ln(p)

So from a microscopic point of view, the entropy of a system increases when the molecular randomness or uncertainty increases.

(stole most of that from my textbook but, eh, gets the job done :-p)
Edit: Your formula is slightly different from mine. It appears that yours takes on the form of a probability mass function, where the sum over all r should equal to one.
 
Last edited:
Ok, thanks guys!
 

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