Definition of specific heat by via entropy

AI Thread Summary
Landau defines specific heat as the heat required to raise a body's temperature by one unit, leading to the equation C_V = T(∂S/∂T)_V for constant volume. The discussion raises confusion about deriving this relationship from the heat-entropy relation, where dQ = TdS, and how to express C_V as (∂Q/∂T)_V. The questioner struggles with understanding why the partial derivative with respect to temperature does not act on T in these equations. The response emphasizes that this is a matter of understanding partial differentiation rather than a physics concept. Mastery of partial differentiation is essential to grasp the definitions of specific heat in thermodynamics.
mSSM
Messages
31
Reaction score
1
In his Statistical Physics book, Landau introduces the specific heat as the quantity of heat which must be gained in order to raise the temperature of a body one by unit.

I don't understand, how he directly jumps to the conclusion that that has to be (let's just say, for constant volume):
<br /> C_V = T\left(\frac{\partial S}{\partial T}\right)_V<br />

If I take a process during which I have no change in volume, I think I can write: \partial Q = T\mathrm{d}S, is that correct? My next thought was then that I could write C_V=\left(\frac{\partial Q}{\partial T}\right)_V. However, now I am stuck, because I do not understand why this should yield the above definition, without acting on the T part of the the heat-entropy relation.EDIT: I would like to add, that I have the same problem with the specific heat's definition via the energy differential \mathrm{d}E = T\mathrm{d}S - P\mathrm{d}V:
C_V = \left(\frac{\partial E}{\partial T}\right)_V

Why does \frac{\partial}{\partial T} not act on T?
 
Last edited:
Science news on Phys.org
You need to go back and learn how partial differentiation is done. This is a mathematics question, not a physics question.
 
I need to calculate the amount of water condensed from a DX cooling coil per hour given the size of the expansion coil (the total condensing surface area), the incoming air temperature, the amount of air flow from the fan, the BTU capacity of the compressor and the incoming air humidity. There are lots of condenser calculators around but they all need the air flow and incoming and outgoing humidity and then give a total volume of condensed water but I need more than that. The size of the...
Thread 'Why work is PdV and not (P+dP)dV in an isothermal process?'
Let's say we have a cylinder of volume V1 with a frictionless movable piston and some gas trapped inside with pressure P1 and temperature T1. On top of the piston lay some small pebbles that add weight and essentially create the pressure P1. Also the system is inside a reservoir of water that keeps its temperature constant at T1. The system is in equilibrium at V1, P1, T1. Now let's say i put another very small pebble on top of the piston (0,00001kg) and after some seconds the system...
Back
Top