Question about entropy=0 in an irreversible process

In summary, the conversation discusses the concept of entropy and its calculation for reversible and irreversible processes. The example of a monatomic gas undergoing a reversible adiabatic path is given, and the question is raised about the possibility of an irreversible path with ΔS=0. It is concluded that any irreversible process will result in ΔS>0 due to the interactions with other systems.
  • #1
Ruko15
1
0
We learned about calculating entropy in my physics 2 class, and i came up with an example that my professor couldn't answer, so I was hoping someone here could shed some light on this for me.

We learned that change in entropy for an irreversible process be represented by changes in entropy of reversible process as long as both reversible and irreversible paths have the same initial and final states.

so here are my two states for 1 mole of a monatomic gas.
P0=1kPa
V0=1m3
T0=[itex]\frac{500000}{4157}[/itex]K≈120.279K

P=500Pa
V=23/5m3≈1.516m3
T=[itex]\frac{906987}{9950}[/itex]K≈91.154K

These two states lie on a reversible adiabatic path.
Calculating the entropy using (using fractions, instead of approximate values)
ΔS=nCvln[itex](\frac{T}{T0})[/itex]+nRln[itex](\frac{V}{V0})[/itex]
ΔS=[itex](1)(\frac{3}{2})(8.314)ln(\frac{≈120.279}{≈91.154})+(1)(8.314)ln(\frac{≈1.516}{1})[/itex]
ΔS=0

Would this not imply then that any real path between these two states is reversible, or that it is possible for an ireversable path to have a ΔS=0? Both of which we learned were not possible.Is this in the correct place or should it be in Homework & Coursework Questions?
 
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  • #2
For an irreversible process (not path!) ending up in that same state the entropy of something else will increase.

For example, if we allow the gas to free expand to the final volume (an irreversible process), its final temperature will be be the same as the initial temperature. To reach the desired state we could place it in contact with a temperature reservoir at 91.154K. The heat transferred will increase the entropy of that reservoir.

Any irreversible process will end up with ΔS>0, when you include all of the interacting parts.
 

1. What is entropy and how is it related to irreversible processes?

Entropy is a measure of the disorder or randomness in a system. In an irreversible process, entropy always increases, meaning that the system becomes more disordered. This is because the system is moving towards thermodynamic equilibrium, where all energy is evenly distributed and there is no useful energy available to do work.

2. Can entropy ever be equal to 0 in an irreversible process?

No, entropy can never be equal to 0 in an irreversible process. This is because in an irreversible process, there will always be some level of energy dispersion or disorder, even if it is very small. Therefore, entropy can never be completely eliminated.

3. What are some examples of irreversible processes?

Some examples of irreversible processes include heat transfer from a hot object to a cold object, diffusion of substances, and the expansion of a gas into a vacuum. These processes all result in an increase in entropy and cannot be reversed without external input of energy.

4. Is there a way to quantify the entropy change in an irreversible process?

Yes, the change in entropy for an irreversible process can be calculated using the equation ΔS = Q/T, where ΔS is the change in entropy, Q is the heat transferred, and T is the temperature at which the heat transfer occurs. This equation is based on the second law of thermodynamics, which states that the total entropy of a closed system always increases in an irreversible process.

5. Why is the increase of entropy in an irreversible process important?

The increase of entropy in an irreversible process is important because it is a fundamental law of nature. It explains why certain processes cannot be reversed and why energy is always dissipated in the form of heat. It also has practical applications, such as in the efficiency of engines and the direction of chemical reactions.

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