# Thermodynamics (Kelvin-Planck statement )

1. Apr 12, 2007

### dotcom

Hi, I got a problem in thermodynamics.

Q. In an isothermal expansion of a gas the energy absorbed by the gas is completely converted to work. Explain how this process can still be consistent with the Kelvin-Planck statement of the second law of thermodynamics.

I thought that's because the question is describing only a part of a cycle and not the full cycle. But i cannot explain further in words.... how can i answer this question in full-mark style?

2. Apr 12, 2007

### Dick

The energy absorbed by the gas is completely converted into the random kinetic energy of the molecules of gas. Is that energy 'work' in the thermodynamic sense?

3. Apr 12, 2007

### dotcom

So,... although energy absorbed by the gas is completely converted to work, the energy is disordered, and so the energy is not actually conserved.
Is that what you mean??

4. Apr 12, 2007

### Dick

Who said energy wasn't conserved??! I'm just saying I don't think the absorbed energy is 'completely converted into work'. But I'm not an expert in this subject. How about posting your analysis of the details and see if someone who is an expert has a comment.

5. Apr 12, 2007

### Dick

Hah! Boy, was I wrong. Told you I wasn't an expert. I've just figured out that the heat absorbed by the gas IS completely converted to kinetic energy. If you can figure out the reasoning that led me to this you might be on the way to filling out the answer in such a way is to get full marks. Think about internal energy of the gas before and after the expansion.

6. Aug 26, 2010

### sasthi hens

why kelvin-plank statement is called cyclic?

7. Aug 27, 2010

### karteekgva

can anyone please derive it and post here the derivation of compressibility factor using vanderwaals equations...
final equatn should be in terms of volume,a and b constants,R..........PLEASE DO IT AS FAST AS POSSIBLE