Isentropic Process and Reversible Process

In summary, the conversation discusses the definitions and characteristics of totally reversible processes and isentropic processes. It is concluded that for a totally reversible process, it must be both internally and externally reversible. An isentropic process is internally reversible and adiabatic, but it is not necessarily a totally reversible process. The reason for this is that although the process may be isentropic, it may still have internal irreversibility that is negated through heat transfer. It is also mentioned that only a cyclic process consisting of totally reversible single path processes will result in a zero entropy change to both the system and environment.
  • #1
noobie_doobie
3
0
Hi all,

Will like to check if my below thoughts are right:

1) For a totally reversible process, it has to be both internally and externally reversible. And the definition of externally reversible means heat transfer between a system and reservoir where the temperature are the same.

2) For an isentropic process, it has to be internally reversible and adiabatic.

From the above 2 definition, can i say that
A) For a totally reversible process, it will not be isentropic since it involve heat transfer, albeit the temperature difference is infinitisimal small.(based on definition of externally reversible)

B) An isentropic process is not a totally reversible process but only an internally reversible process


For another question on the same topic, in an adiabatic reversible expansion of a piston system( i.e isentropic) , can I visualise the reason this process is seen as isentropic is because although the volume increases, meaning the molecules are more random(increase entropy), the counter effect is brought about by the reduction in pressure and temperature, hence slowing down the molecule speed, resulting in a zero entropy change??
 
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  • #2
noobie_doobie said:
Hi all,

Will like to check if my below thoughts are right:

1) For a totally reversible process, it has to be both internally and externally reversible. And the definition of externally reversible means heat transfer between a system and reservoir where the temperature are the same.

2) For an isentropic process, it has to be internally reversible and adiabatic.

From the above 2 definition, can i say that
A) For a totally reversible process, it will not be isentropic since it involve heat transfer, albeit the temperature difference is infinitisimal small.(based on definition of externally reversible)

B) An isentropic process is not a totally reversible process but only an internally reversible process


For another question on the same topic, in an adiabatic reversible expansion of a piston system( i.e isentropic) , can I visualise the reason this process is seen as isentropic is because although the volume increases, meaning the molecules are more random(increase entropy), the counter effect is brought about by the reduction in pressure and temperature, hence slowing down the molecule speed, resulting in a zero entropy change??

I don't quite understand how you conclude that isoentropic process is not reversible

Yes to the "another question"
 
  • #3
I think maybe it is good to define that the only kind of reversible processes are a)internally reversible, b)externally reversible and c)totally reversible. We should avoid using the term general term 'reversible process' as in many websites since there are subtle differences between each reversible process which have to be considered.

Going back to my conclusion in point B) that isentropic process is not totally reversible, this is because the process might have internal irreversibility but is negated through heat transfer. Hence, with internal irreversibility, the process is no more totally reversible. One question, although the process is isentropic for this case, does it implies that the surrounding has be to isentropic too??

As for my statement A), maybe I will rephrase to say that
i) for a totally reversible single path process, it might not be isentropic since it involve heat transfer, albeit the temperature difference is infinitisimal small.(based on definition of externally reversible). This can be seen from the isothermal expansion in Carnot cycle, which is a totally reversible process, yet not isentropic.

ii) for a totally reversible single path process, only an adiabatic expansion is isentropic, as seen from adiabatic expansion in Carnot Cycle.

iii) only a cyclic process, consisting of totally reversible single path processes, will result in a zero entropy change to the system and environment.
A cyclic process, consisting a mixture of totally reversible single path and isentropic(not necessary reversible) single path, might cause the system to have zero entropy change but not the environment.
 

1. What is an isentropic process?

An isentropic process is a thermodynamic process in which the entropy remains constant. This means that the system does not exchange heat with its surroundings, and any work done on or by the system is reversible. It is often used to model idealized thermodynamic systems.

2. How is an isentropic process different from an adiabatic process?

An isentropic process is a special case of an adiabatic process, where no heat is exchanged with the surroundings. In an adiabatic process, the entropy may change due to work done on or by the system, while in an isentropic process, the entropy remains constant.

3. What is a reversible process?

A reversible process is a thermodynamic process that can be reversed by infinitesimal changes in the conditions of the system. This means that the process can be undone without any change in the system's entropy. It is often used as an idealized model for thermodynamic processes.

4. How is a reversible process different from an irreversible process?

A reversible process is a process that can be reversed without any change in entropy, while an irreversible process cannot be undone without some increase in entropy. Reversible processes are idealized models, while most real-world processes are irreversible.

5. What are some examples of isentropic and reversible processes?

An example of an isentropic process is the expansion of an ideal gas in a perfectly insulated container. An example of a reversible process is an idealized Carnot cycle, where the system undergoes reversible adiabatic and isothermal processes. Other examples include reversible chemical reactions and reversible phase transitions.

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