Heat capacity (statistical physics)

[broegger]

Hi. I've just started a course on statistical physics and the first assignment is this:

A system possesses 3 energy levels, $$E_1 = \epsilon,$$ $$E_2 = 2\epsilon$$ and $$E_3 = 3\epsilon$$. The degeneracy of the levels are g(E1) = g(E3) = 1, g(E2) = 2. Find the heat capacity of the system.

I've forgotten all this thermodynamics stuff, so I would appreciate some hints :-)

 

[broegger]

Anyone? Please

 

[Gokul43201]

If you are given a description of a system, what quantity do you first compute, from which you can determine other thermodynamic quantities ?

 

[broegger]

Yes, yes, the partition function, I know :-)

 

[marblepony]

sum over states to get Q

Q= exp{-B.E) + 2exp{-B.2E} + exp{-B.3E}

B=kT Q=partition E=energy (two in front of second term beacuse of degenercy)


U= - Diff (lnQ) w.r.t (B)

U= internal energy prof can be found ( http://www.chem.arizona.edu/~salzmanr/480b/statt01/statt01.html)... if you are interested

gives U= E.exp(-B.E) + 4E.exp(-B.2E) + 3E.exp(-B.3E)

makes sense highest energy has least probability of being populated but contributes three times as much to internal energy when it is. same would apply to the middle state but there is two of them so it is four instead of two.