# Reversible processes need to be ONLY isothermal or adiabatic?

• jaumzaum
In summary, the conversation discusses the requirements for a process to be reversible and whether it is necessary for all reversible processes to only involve isothermal and adiabatic transformations. It also mentions examples of other reversible processes, such as isobaric and isochoric processes.
jaumzaum
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?

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.

Last edited:
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

Delta2

## 1. What is a reversible process?

A reversible process is a thermodynamic process that can be reversed by making infinitesimal changes to its parameters, such as temperature and pressure, without causing any change in the surroundings. This means that the system and its surroundings can be brought back to their initial states without any net change in energy or entropy.

## 2. Why do reversible processes need to be isothermal or adiabatic?

This is because these two types of processes are the only ones that can maintain a constant internal energy of the system. In an isothermal process, the temperature of the system remains constant, while in an adiabatic process, there is no heat exchange between the system and its surroundings. This ensures that the system remains in thermal equilibrium throughout the process, making it reversible.

## 3. Can a reversible process be both isothermal and adiabatic?

No, a process cannot be both isothermal and adiabatic at the same time. This is because an isothermal process involves heat exchange with the surroundings, while an adiabatic process does not. Therefore, a process can only be either isothermal or adiabatic, but not both.

## 4. Are all reversible processes spontaneous?

No, not all reversible processes are spontaneous. A reversible process simply means that it can be reversed without any change in the surroundings. However, the spontaneity of a process depends on the conditions under which it occurs. For example, a reversible process can be spontaneous if it takes place under certain conditions, such as a decrease in temperature.

## 5. How are reversible processes different from irreversible processes?

Reversible processes can be reversed without any change in the surroundings, while irreversible processes cannot be reversed. In an irreversible process, there is a net change in energy and/or entropy in the system and its surroundings. This means that irreversible processes are not in thermal equilibrium and cannot be brought back to their initial states without causing changes in the surroundings.

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