[Statistical Physics] Microstates in a large system/Boltzmann entropy

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Homework Help Overview

The discussion revolves around estimating the number of microstates in a system of nitrogen gas at standard temperature and pressure (S.T.P.) using concepts from statistical physics, specifically Boltzmann entropy.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply the entropy equations for an ideal gas but expresses uncertainty about the mass variable in the equations. They calculate the number of molecules and plug values into the equations, leading to a question about the validity of their approach and the resulting large number of microstates.

Discussion Status

Participants are engaging with the original poster's calculations, with some offering validation of the approach while questioning the units used for entropy. There is acknowledgment of the challenges in handling large numbers in calculations.

Contextual Notes

There is a noted ambiguity regarding the mass variable in the entropy equations, and the original poster is working under the constraints of homework rules that may limit the information they can access.

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Homework Statement



For a box containing 1m^{3} of nitrogen at S.T.P., estimate the number of microstates which make up the equilibrium macrostate.


Homework Equations



S = Nk_{b}(ln\frac{V}{N} + \frac{5}{2} + \frac{3}{2}ln\frac{2πmk_{b}T}{h^{2}})

where the entropy of a volume, V , of an ideal gas, containing N molecules of mass m at temperature T

S = k_{b}lnΩ


The Attempt at a Solution



First off I don't know which mass it is asking for in the equation. Is it the mass of each individual molecule? Or the mass of all the molecules? Or the molar mass? Either way I tried them all but still couldn't get an answer.

I first worked out what N was.

40.82 mols in 1m^{3} of an ideal gas
1 mol = 6.022x10^{23}
∴ N = 2.46x10^{25}

I let m = 4.652x10^{-26} kg (the mass of a nitrogen molecule)

Plugging those numbers into the first equation gives entropy, S = 6122

Now I know the number of microstates is going to be huge, but from the second equation:

lnΩ = S/k_{b} = 4.44x10^{26}

∴Ω = e^{4.44x10^{26}}

which brings about a "math error".

Am I going about this in the right way?

Cheers
 
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Maybe a mod could move this into the Advance forum?
 
That seems correct to me, except for the missing units. S=6122 (what units?).
You only get a math error if you try to plug that huge number into a typical calculator. Why wold you do that?
 
Ah that's good then. I just thought it was an unreasonably large number.

JK^{-1}
 

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