The discussion revolves around the definition and implications of reversible processes in thermodynamics, exploring theoretical concepts, natural occurrences, and the limitations of such processes. Participants examine the conditions under which a reversible process can be defined and why they are considered unattainable in real-world scenarios.
Participants express differing views on the nature of reversible processes, with some asserting that they are purely theoretical and unattainable in practice, while others provide examples of processes that approach reversibility. The discussion remains unresolved regarding the implications of these definitions and examples.
Limitations include the assumptions made about the universe's state during reversible processes and the dependence on ideal conditions that may not be achievable in reality.
The system and surroundings = universe. But you are only interested in the part of the universe that is affected by the process. The universe is constantly changing so you can never actually restore the same state of the universe. So we say that the system and surroundings can be restored to their initial state IF you were to assume that there were no other changes occurring other than those relating to the particular thermodynamic process you are concerned with.failexam said:I have seen a reversible process defined as one in which the system and surroundings are restored to their initial state without change elsewhere. As far as I am aware, the system and the surroundings completely occupy the universe. So, I am failing to understand what elsewhere means in this context.
Please enlighten me.
Reversible processes require heat to flow due to infinitessimal temperature differences and changes in volume to occur due to infinitesimal pressure differences, so they take an infinite time. The reversible process represents a limit that can be approached but never achieved.failexam said:I am also wondering why reversible processes do not occur in nature. Anyone wants to take on the challenge?
I am also wondering why reversible processes do not occur in nature. Anyone wants to take on the challenge?
Andrew Mason said:The reversible process represents a limit that can be approached but never achieved.
Andrew Mason said:But you are only interested in the part of the universe that is affected by the process.
Andrew Mason said:The universe is constantly changing so you can never actually restore the same state of the universe.
A reversible process is a theoretical limit. The assumption is that the rest of the universe is not affected during the time it takes for the process to occur.failexam said:How can we be sure that the entire universe is not affected by the process?
I am not sure what you mean. Can you give an example?But are we not considering an ideal universe where the parameters of only the system can be altered? In other words, are we not considering a universe where the surroundings can modify only if there is a change within the system?
A change of state due to an infinitessimal temperature difference between the substance and the surroundings would be reversible. But this does not occur in nature. It would take an infinite amount of time. A change of state in nature can be close to reversible. For example, an ice cube in a glass of ice water at 0C. For it to melt reversibly, the room would have to be kept at 0C. But if it is in a room at 0C the ice will never melt. If the room is 1C, the ice will eventually melt but slowly. That would be close to a reversible process. If the room is kept at 20C it will melt much faster, but at the expense of a greater increase in entropy.Studiot said:Change of state eg melting is an example of a natural reversible process.