Understanding Quasi-Static Processes and Reversibility in Thermodynamics

In summary: So, in summary, a gas undergoing changes in its thermodynamic states must do so through a quasi-static process in order for it to be reversible. Otherwise, the process will be irreversible due to violations of the second law of thermodynamics.
  • #1
Oerg
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Hi

I have difficuly understqanding this:

If a gas undergoes changes in its thermodynamic states, then the process is irrversible unless it is conducted at such an infinitely slow pace that at every instant of the process, the system is in thermodynamic equilibrium.Ok, so the text gives the example of a gas expanding into a vacuum without heat transfer like a adiabatic process. The problem is: The text says that the expanding gas does no work and after its expansion, we cannot reverse it because compressing the gas means that work is removed by the system from the surroundings resulting in a rise in temperature which cannot be dissipated as work completely according to the second law of thermodynamics.

I agree with the text. Except that what if the gas was expanding on its own uin a non quasi static manner? It would have done work against the surroundings, the temperature of the gas would have decreased and I can reverse all this by supplying the work done on me by compressing the gas and the gas's temperature would have risen to where it was initially. This is where I do not see how a quasi static process is essential to ensure that the provess is reversible.
 
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  • #2
In order for a process to be considered reversible, it must take place slowly enough that the system is always in equilibrium. This means that if the process is occurring too quickly and the system is not in equilibrium, then the process is irreversible. A quasi-static process is one that takes place so slowly that at every instant of the process, the system is in thermodynamic equilibrium. This ensures that the process can be reversed without running into any issues with the second law of thermodynamics.
 
  • #3


First, let's define what quasi-static processes and reversibility mean in thermodynamics. A quasi-static process is one in which the system undergoes small, incremental changes in its thermodynamic state, while maintaining thermodynamic equilibrium at every instant. This means that the system is always in a state of balance, and there is no net transfer of energy or matter between the system and its surroundings.

On the other hand, a reversible process is one in which the system can be returned to its initial state by reversing the process without any loss of energy or increase in entropy. This means that the process is able to be reversed without any irreversibilities or losses.

Now, going back to your example of a gas expanding into a vacuum without heat transfer. In this case, the process is irreversible because the gas expands quickly and does not have time to reach thermodynamic equilibrium at every instant. This means that the system is not in balance and there is a net transfer of energy from the gas to the surroundings. This results in a decrease in the gas's temperature, which cannot be reversed by simply compressing the gas, as you mentioned.

On the other hand, if the gas was expanding in a quasi-static manner, it would do work against the surroundings slowly and gradually, allowing the system to reach thermodynamic equilibrium at every instant. This means that the gas's temperature would not decrease significantly, and the process would be reversible.

In summary, a quasi-static process is essential for reversibility because it ensures that the system is always in thermodynamic equilibrium, and there is no net transfer of energy or matter between the system and its surroundings. This allows the process to be reversed without any losses or irreversibilities. I hope this helps clarify your understanding of quasi-static processes and reversibility in thermodynamics.
 

1. What is a quasi-static process in thermodynamics?

A quasi-static process is a thermodynamic process that occurs very slowly and gradually, with the system remaining in thermal equilibrium at all times. This means that the system is always close to its equilibrium state and can be considered to be in equilibrium at each intermediate step of the process.

2. How does a quasi-static process differ from an irreversible process?

A quasi-static process is reversible, meaning that it can be reversed at any point without leaving any change in the surroundings. On the other hand, an irreversible process cannot be reversed and results in a net change in the surroundings.

3. What is the importance of understanding quasi-static processes in thermodynamics?

Understanding quasi-static processes is important in thermodynamics because it allows us to make accurate predictions about the behavior of a system and its surroundings. It also helps in analyzing real-life processes and designing efficient systems.

4. Can a quasi-static process occur in a closed system?

Yes, a quasi-static process can occur in a closed system as long as the system is in thermal equilibrium at all times. This means that the temperature, pressure, and other thermodynamic properties of the system remain constant throughout the process.

5. How do we mathematically represent a quasi-static process?

A quasi-static process is represented mathematically by a series of equilibrium states. These equilibrium states can be connected by a smooth curve on a thermodynamic diagram, such as a pressure-volume or temperature-entropy diagram. The area under this curve represents the work done by the system during the process.

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