Hypothetical cyclic process- does it violate the thermodynamic laws?

In summary, the conversation discusses a cyclic process in which 800J of energy is transferred from a reservoir at 800K and 600J of energy from a reservoir at 600K. 400J of heat is rejected to a reservoir at 400K and 1000J of work is done. The first and second laws of thermodynamics are considered, and it is determined that the process does not violate either law. The concept of entropy is briefly mentioned, with the conclusion that the overall entropy of the system increases after each cycle. The individual's logic is questioned and further discussion ensues.
  • #1
trelek2
88
0
Consider the following cyclic process:
Each cycle 800J of Energy is transferred from a reservoir at 800K and 600J of energy from a reservoir at 600K. 400J of heat is rejected to a reservoir at 400K and 1000J of work is done.

I think that the process doesn't violate the first or second laws of thermodynamics:
1st law: dU= dQ+dW
The internal energy of the system is constant: dU= 600+800-1000-400 = 0 so first law is not violated.
2nd law: Taking the Kelvin Planck statement: The engine not only extracts heat from a source and turns it into work but also has to pass some heat on to a colder reservoir, therefore I think that the second law is also not violated.
If I'm mistaken please correct me. If I'm not please reassure me that my logic is correct.
 
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  • #2
  • #3
We haven't really covered entropy in the lectures yet, so i don't think I'm ment to be using that. Nevertheless, I looked at it just now and it seems to me that the overall entropy of the system increases after each cycle, so the 2nd law is not violated, is that right?
 
  • #4
trelek2 said:
it seems to me that the overall entropy of the system increases after each cycle

How did you figure that?
 
  • #5
trelek2 said:
it seems to me that the overall entropy of the system increases after each cycle

How did you figure that?
 
  • #6
I found that the change in entropy is equal to amount of energy added or extracted at a given temperature. So we take out 1 twice and put back in once for sure. I'm not sure what to do with the work. I thought it would be increasing entropy of the surroundings by 1000J/700K which is over 1?
 

1. What is a hypothetical cyclic process?

A hypothetical cyclic process is a theoretical process that involves a system undergoing a series of changes and returning to its original state. It is often used in thermodynamics to understand the behavior of a system over a period of time.

2. How does a hypothetical cyclic process violate the thermodynamic laws?

A hypothetical cyclic process does not violate the thermodynamic laws. In fact, it follows the first and second laws of thermodynamics, which state that energy cannot be created or destroyed and that the total entropy of a closed system will always increase.

3. Can a hypothetical cyclic process be achieved in reality?

No, a hypothetical cyclic process cannot be achieved in reality as it is a theoretical concept. However, real-life processes can often be approximated as cyclic processes, and studying them can provide valuable insights into the behavior of systems.

4. What is the significance of studying hypothetical cyclic processes?

Studying hypothetical cyclic processes allows scientists to better understand the principles of thermodynamics and their applications in real-world systems. It also helps in developing more efficient and sustainable processes in various fields such as engineering, chemistry, and biology.

5. Are there any limitations to using hypothetical cyclic processes in thermodynamics?

Yes, there are limitations to using hypothetical cyclic processes in thermodynamics. They do not take into account external factors such as friction, heat loss, and irreversibility, which can affect the overall efficiency of a real-life process. Therefore, they are used as a simplified model and may not always accurately reflect real-world scenarios.

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