Solving the Entropy Puzzle: Blundell and Blundell Q&A

In summary, the conversation discusses a question regarding the change in entropy for a van der Waals gas in two different processes. The first part of the question is answered correctly, but there is confusion about the change in temperature in the second part. The conversation concludes with a revision of the change in entropy, as it is not the same for both processes due to cooling of the gas in one of the processes.
  • #1
Jesssa
51
0
Hello,

This is a question I've been working on out of blundell and blundell,

http://imageshack.us/a/img560/3342/entwopy.jpg [Broken]

The red box is my answers to the question which I am pretty sure are ok.

I am having trouble with the very last part of the question.

By the logic of the first part, the entropy would be the same with the VDW gas in both cases right (cases a and b)? Since entropy is a state variable.

But how can you find the change in temperature?

Thank you
 
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  • #2


You know that ΔU=Q+W. If it is free expansion into vacuum, what is the heat exchanged and the work done by the gas during the process?

ehild
 
  • #3


Ah right,

The work done by the gas will be zero and there will be no heat exchanged (assuming the enclosure is insulated).

So

ΔU=0=(3/2)nRΔT-n2a/αV + n2a/V


(3/2)RΔT=na/αV -n2a/V =na(1/α-1)/V

(3/2)RΔT=-na(-1/α+1)/V = -na(-1/α+1)/V=-na(α-1)/αV

So ΔT<0 i.e. decreases by an amount proportional to (α-1)/α

Thanks!
 
  • #4


Revise the change of entropy, too, as not only the volume but also the temperature changes.

ehild
 
  • #5


Oh, did you suggest that because there is a mistake in the working I posted in the picture and the second post, or do you mean in general?
 
  • #6


You said the change of entropy would be the same for the van der Waals gas in both processes a and b (isotherm expansion and expansion into vacuum) as the gas arrives to the same state. It is not true for the VDW gas as it cools down in process b.

ehild
 
  • #7


Oh sorry,

Thanks again for all your help!
 

1. What is the entropy puzzle?

The entropy puzzle refers to the concept of how order can emerge from disorder in the universe. It is the idea that despite the natural tendency of systems to move towards a state of disorder or randomness, we observe complex and organized structures in the universe, such as living organisms and galaxies. This puzzle has been a topic of debate and research among scientists for centuries.

2. Who are Blundell and Blundell?

Blundell and Blundell are a father-son duo of scientists who have made significant contributions to the field of chemistry and physics. Sir Michael Blundell is a theoretical physicist and professor at the University of Oxford, while his son Prof. Stephen Blundell is a condensed matter physicist at the University of Oxford. They have collaborated on numerous research projects and have co-authored the book "Concepts in Thermal Physics" which discusses the topic of entropy in detail.

3. Why is solving the entropy puzzle important?

The concept of entropy is crucial in understanding the fundamental laws of thermodynamics, which govern energy and matter in the universe. Solving the entropy puzzle would not only help us understand the origin of complex systems in the universe but also provide insights into the behavior of materials and energy. It could potentially lead to advancements in various fields such as energy production, material science, and even cosmology.

4. How have Blundell and Blundell contributed to the study of entropy?

Blundell and Blundell have made significant contributions to the study of entropy through their research and publications. They have explored the concept of entropy from a theoretical and experimental perspective and have proposed new ideas and models to explain its behavior. Their work has helped advance our understanding of entropy and its role in the universe.

5. What are some potential solutions to the entropy puzzle?

There are several theories and hypotheses that attempt to explain the emergence of order from disorder in the universe. Some of these include the theory of self-organization, which suggests that complex systems can arise spontaneously from simple interactions. Another theory is the idea of dissipative structures, which proposes that energy flows through a system can create order. Other potential solutions include the role of quantum mechanics and the possibility of multiple universes. However, the entropy puzzle is still an ongoing topic of research and does not have a definitive solution yet.

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