Thermal Physics: Energy change due to compression

In summary, the passage from the textbook discusses a system with a quantum state and energy that is a function of the volume. The system undergoes a slow compression while remaining in the same quantum state, with the external force causing a change in energy. The question is raised about how this can be considered a reversible process, given the changing energy, and whether it is in contact with a thermal reservoir. The conversation also touches on the combination of quantum and thermodynamic views in the same description.
  • #1
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This is not a homework problem but rather a passage from my textbook that I don't understand. I don't think I quite understand the concept of reversible processes. Here is the passage from my book:

"Consider a system in the quantum state s of energy Es. We assume Es to be a function of the volume of the system. The volume is decreased slowly by application of an external force. Let the volume change take place sufficiently slowly that the system remains in the same quantum state s throughout the compression...The mechanical work done on the system by the pressure in a contraction appears as the change of energy of the system."

My question is:
How is it possible that the system can remain in the same quantum state throughout the compression if the energy is changing? (I believe the system under consideration is in contact with a thermal reservoir). Is this a reversible process?

Thank you!
 
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  • #2
What a strange book? What book is it?

Pressure and temperature are concepts that apply to the average behavior of large numbers of particles. Quantum mechanical analysis applies to only a few particles at a time.

I find it hard to imagine why it would be useful to try to blend quantum and thermodynamic views in the same description.
 
  • #3
It's thermodynamics and statistical mechanics. Quantum is actually a pre-req.
 

1. What is thermal physics?

Thermal physics is a branch of physics that deals with the study of energy and how it relates to the motion and behavior of particles at the microscopic level.

2. What is energy change due to compression?

Energy change due to compression is the change in energy that occurs when a gas is compressed. This can lead to an increase in temperature and overall energy within the system.

3. How does compression affect energy?

Compression of a gas leads to an increase in energy due to the work done on the gas, which causes an increase in temperature. This can also lead to a change in the internal energy and pressure of the gas.

4. What is the relationship between compression and temperature?

The relationship between compression and temperature is described by the Ideal Gas Law, which states that as the pressure on a gas increases, its temperature will also increase. This is because the gas molecules are forced closer together, resulting in more frequent collisions and an increase in kinetic energy.

5. How is energy change due to compression measured?

Energy change due to compression can be measured using various techniques such as calorimetry, where the change in temperature of a substance is used to calculate the energy change. Other methods include using pressure-volume graphs or directly measuring the change in internal energy of the system.

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