Reversible processes need to be ONLY isothermal or adiabatic?

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Discussion Overview

The discussion centers on whether all reversible processes must consist solely of isothermal and adiabatic transformations. Participants explore the characteristics of reversible processes and consider examples beyond the Carnot cycle.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions if all reversible processes must be isothermal or adiabatic, noting that the Carnot cycle meets this criterion.
  • Another participant asserts that all reversible processes need to be quasi-static and suggests that there may be quasi-static processes that are neither adiabatic nor isothermal.
  • A different participant argues that reversible processes can include isobaric (constant pressure) and isochoric (constant volume) processes, emphasizing the importance of quasi-static conditions for thermodynamic equilibrium.
  • A later reply reiterates the initial question and discusses the necessity of infinitesimal temperature differences for reversible heat flow, suggesting that an idealized Otto cycle could be reversible if such conditions are met during isochoric heat transfers.

Areas of Agreement / Disagreement

Participants express differing views on whether reversible processes can include transformations other than isothermal and adiabatic, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Participants mention the need for quasi-static conditions and thermodynamic equilibrium, but do not fully resolve the implications of these requirements on the nature of reversible processes.

jaumzaum
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My question is: Do ALL the reversible process need to be composed of ONLY isothermal and adiabatic transformations? Carnot cycle satisfy this, but what other cycle would be also reversible?
I know that for a process to be reverisble it has to be almost-static, have no dissipative force, and no heat and finite temperature variation simultaneously. Does it imply only isothermal and adiabatic?
 
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All the reversible process need to be quasi-static. Are there neither adiabatic nor isothermal quasi-static process ? I think so, but cannot show you a good example now.
 
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No, there are reversible processes like isobaric(constant pressure) or isochoric (constant volume). Generally any process which is quasi static meaning that for each time instant of the process, the gas is in thermodynamic equilibrium, which means that the pressure (and temperature and probably density) of the gas has the same value across the whole region of the gas.
 
jaumzaum said:
My question is: Do ALL the reversible process need to be composed of ONLY isothermal and adiabatic transformations? Carnot cycle satisfy this, but what other cycle would be also reversible?
I know that for a process to be reverisble it has to be almost-static, have no dissipative force, and no heat and finite temperature variation simultaneously. Does it imply only isothermal and adiabatic?
In order for a thermodynamic cycle to be reversible all heat flow must occur at an infinitesimal temperature difference between the system and surroundings (which is what theoretically occurs in the isothermal part of the idealized Carnot cycle). If the system is using constant temperature reservoirs for heat flow to and from the system, then this necessarily requires isothermal heat flow.

Theoretically one could have a reversible Otto cycle if one could figure out a way of maintaining an infinitesimal temperature difference between the system and surroundings for the heat flow at constant volume (isochoric). One could approach that idealized situation with a series of reservoirs with slightly different temperatures in contact with the system to permit the isochoric heat transfers. See the discussion in this PF thread.

AM
 
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