Is the 3rd law of thermodynamics necessary?

In summary, the conversation discusses the possibility of deriving the 3rd law of thermodynamics from the 2nd law. The argument is made that a thermal reservoir at absolute zero would result in a more efficient engine than Carnot's, but this is impossible based on the 2nd law. The need for a 3rd law is also questioned, with the response that it is necessary to understand the relationship between temperature and entropy. It is mentioned that the 3rd law cannot be derived and is instead proven for every thermodynamic system.
  • #1
Feynmanfan
129
0
Here's a question my thermodynamics teacher was unable to answer. I present it to you and see where the flaw of my argument is.

Is it possible to derive the 3rd law of thermodynamics from the 2nd law?

Carnot's theorem (no other machine than Carnot's has maximum efficiency) tells us that when the process is reversible (Carnot engine)
Q2/Q1=T2/T1 and therefore it is possible to define an absolute temperature. Now if there were a thermal reservoir at T2=0, it would be possible to have a more efficient engine than Carnot's. T2=0 -> Q2=0 and efficiency=1
This argument holds the other way around, it is impossible to have Q2=0 (2nd law) therefore T2=0 cannot be zero.

Our teacher argues that Einstein tackled this problem and demostrated that it has no physical sense to talk about ADIABATIC and ISOTHERMAL processes at the same time (I mean simultaneously). This, I do not understand.

What do you think? Why do we need a 3rd law? Thanks for your help.
 
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  • #2
Of course it is necessary
the 3rd law states that
" As the temperature tends to absolute zero the entropy also tends to zero. "

It must remembered that the entropy gives the direction of a process.
therefore, if entropy = o there is no thermodynamic process and the third law gives the relation temperature and entropy.
Sampath :smile:
 
  • #3
No, it isn't possible. Else it would be stated as a theorem in theoretical thermodynamics. It can be however proven as being valid for every thermodynamical system for which one derives the thermodynamics starting from (equilibirum) statistical mechanics...

Daniel.
 
  • #4
I get it.
Sampath
 
  • #5
I don't.

~Kitty
 

1. What is the 3rd law of thermodynamics?

The 3rd law of thermodynamics states that the entropy of a perfect crystal at absolute zero temperature is zero. In other words, there is a state of absolute order and no randomness at absolute zero temperature.

2. Why is the 3rd law of thermodynamics necessary?

The 3rd law of thermodynamics is necessary because it provides a baseline for measuring entropy and understanding the behavior of systems at low temperatures. It also helps to explain why some processes are impossible to reverse.

3. How does the 3rd law of thermodynamics relate to the other laws?

The 3rd law of thermodynamics is closely related to the 1st and 2nd laws of thermodynamics. The 1st law states that energy cannot be created or destroyed, while the 2nd law states that the total entropy of a closed system will always increase. The 3rd law provides a specific condition for the behavior of entropy at absolute zero temperature.

4. Can the 3rd law of thermodynamics be violated?

No, the 3rd law of thermodynamics is a fundamental law of nature and has been tested and confirmed through various experiments. It is considered to be a universal law that cannot be violated.

5. How does the 3rd law of thermodynamics impact real-world applications?

The 3rd law of thermodynamics has many practical applications, such as in the design of refrigeration systems and understanding the behavior of materials at very low temperatures. It also plays a crucial role in fields such as chemistry, physics, and engineering, allowing scientists and engineers to predict and control the behavior of systems at low temperatures.

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