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Covers the study of (primarily homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using the tag: [statistical-mechanics].
7
votes
Accepted
Does specific heat capacity depend on temperature of the substance?
As a consequence of the 3rd law of thermodynamics or more generally a finite value of residual entropy, you also need to have a vanishing of the heat capacity at low temperature. …
6
votes
Accepted
Fugacity in the classical limit
It depends on what you are interested in. It is often more physically relevant to think at fixed number of particles rather than fixed $\mu$, so $\mu$ picks up an implicit temperature dependence.
Take …
5
votes
Accepted
Definition of the pressure in statistical mechanics
While you can choose any two independent variables as your basis function to express any quantity, you need to be careful in the choice of your variables when defining new quantities as derivatives. D …
5
votes
Accepted
Relation between specific heats for a magnetic system
Neglecting pressure and volume, your energy is:
$$
dU=TdS+HdM
$$
You can therefore apply the same method by formally substituting $P\to-H$ and $V\to M$. The analogue for enthalpy is:
$$
\mathcal H = U …
4
votes
How to choose the microstates so that thermodynamical entropy coincides with statistical mec...
Actually, thermodynamic entropy depends on the definition of your system in some sense, just as the statistical entropy depends on the micro-states.
The classic example is Gibbs’ paradox. If you have …
4
votes
Taking derivative with respect to quantum canonical ensemble expectation value
On a side note, you can avoid the Trotter formula by using instead the standard interaction picture (if you are already familiar with it from previous QM courses). I will write $\partial_{x_i} = \part …
3
votes
If boiling of water involves change in internal energy, then why does the temperature remain...
This will rather lead to the consideration of free enthalpy $G = F+pV$ which should be more familiar if you've done chemistry or thermodynamics. The discussion is essentially the same though. …
3
votes
Quasi-static processes that are not reversible
Quasistatic processes encompass reversible processes. The inclusion is strict, because there are some irreversible quasistatic transformations.
A typical example of a quasi static process would be a s …
3
votes
Accepted
Jacobian determinants in thermodynamics and a different approach to deriving the Maxwell rel...
Question 1
Yes, you can derive this from the first law of thermodynamics. For a cyclic process $W=Q$, heat equals work. …
3
votes
Why is entropy a quantification of the typical fluctuation of internal energy around the exp...
In the following, I'll set $k_B=1$. Usually, the fluctuations of energy are rather captured by heat capacity. This is captured by the following formula saying that heat capacity is proportional to the …
3
votes
Accepted
Clarifying the definition of pressure in statistical physics
Actually, your question has little to do with statistical mechanics, but more about classical thermodynamics. … It typically holds in the thermodynamic limit, which is why for most applications classical thermodynamics applies. …
3
votes
Microcanonical ensemble through Maximum Entropy method
In general, the two distributions have little to do with each other. After all, $\rho_e$ is fixed but $\rho_{mc}$ depends on the variable energy $E$. I will therefore reformulate your question as: can …
2
votes
Accepted
Mixing identical gases in different states (Gibbs paradox)
Yes, it works without any problems. I’ll just add that you can do it all in one go by modifying the expression of your entropy:
$$
S =nc_v\ln(T/T_0)+nR\ln\left(\frac{V/n}{ V_0/n_0}\right)+ns_0
$$
with …
2
votes
Deriving total temperature of a composite system
Assuming your system is isolated you want to maximize $S$ with fixed $U$ according to the second law. More concretely, you want to maximize $S=S_A+S_B$ by only varying $U_A,U_B$ under the constraint $ …
2
votes
Accepted
How does one "invert" derivatives for intensive variables?
The fact that the variables are intensive/extensive is irrelevant. These partial derivatives just come from differential calculus.
Slight notation change, I’ll use $M$ for the magnetic moment instead …