# Irrev. adiabatic process entropy >0 or =0?

• sparkle123
In summary: Delta S (sys) > 0 for irreversible adiabatic processes in closed systems. However, since Delta S = 0 for reversible adiabatic processes and entropy is a state function, it is believed that Delta S = 0 for irreversible adiabatic processes as well. However, this is not the case as Delta S > 0 for irreversible processes due to the fact that entropy is a state function and is path dependent. Therefore, the final states for adiabatic reversible and irreversible processes are not the same, leading to a difference in Delta S values. This is evident when applying the first law to determine the change in internal energy for each case. In summary, for closed systems, Delta
sparkle123
My textbook says that
Delta S (sys) > 0 for irrev. ad. proc., closed syst
(or see http://www.britannica.com/EBchecked/topic/5898/adiabatic-process if you don't believe me)

but since Delta S = 0 for reversible adiabatic process and entropy is a state function,
shouldn't Delta S = 0 for irreversible adiabatic process = 0 too?

I don't understand your justification for ΔS = 0 for an irreversible process.

By virtue of being an irreversible process ΔS > 0.

i thought entropy being a state function means it is path dependent so as long as initial and final states are the same, ΔS is the same.
thus ΔS for adiabatic reversible should equal ΔS for adiabatic irreversible (for same initial, and final states) ?
Thanks so much!

sparkle123 said:
i thought entropy being a state function means it is path dependent so as long as initial and final states are the same, ΔS is the same.
thus ΔS for adiabatic reversible should equal ΔS for adiabatic irreversible (for same initial, and final states) ?
Entropy is indeed a state function. But are the final states the same for an adiabatic quasi-static (reversible) expansion and an adiabatic free (irreversible) expansion? Hint: apply the first law to determine the change in internal energy in each case.

AM

It is correct that the change in entropy for a reversible adiabatic process is equal to zero, as the process is considered to be thermodynamically efficient and does not result in any net increase in entropy. However, for an irreversible adiabatic process, the change in entropy is greater than zero. This is because irreversible processes involve dissipative effects, such as friction or heat transfer, which result in an increase in the overall entropy of the system. This increase in entropy is a result of the loss of useful energy and the conversion of that energy into less organized forms. Therefore, for an irreversible adiabatic process, the change in entropy is greater than zero, as stated in your textbook.

## 1. What is an irreversible adiabatic process?

An irreversible adiabatic process is a thermodynamic process in which there is no transfer of heat between the system and its surroundings, and the system is unable to return to its initial state without the assistance of an external agent.

## 2. How does an irreversible adiabatic process differ from a reversible adiabatic process?

In a reversible adiabatic process, the system can return to its initial state without any external assistance, while in an irreversible adiabatic process, this is not possible. Additionally, a reversible process follows a specific path on a thermodynamic diagram, while an irreversible process does not.

## 3. What does it mean for the entropy to be greater than or equal to 0 in an irreversible adiabatic process?

In an irreversible adiabatic process, the entropy of the system will always either increase or stay the same. This is due to the fact that in an irreversible process, there is always an increase in disorder, leading to an increase in entropy.

## 4. Can the entropy of a system decrease during an irreversible adiabatic process?

No, the entropy of a system can never decrease in an irreversible adiabatic process. This is because the system is isolated and there is no transfer of heat, so there is no way for the disorder to decrease.

## 5. What is the significance of the entropy being greater than 0 in an irreversible adiabatic process?

The fact that the entropy is greater than 0 in an irreversible adiabatic process indicates that there is an irreversible loss of energy in the system. This loss of energy is due to the increase in disorder and the inability of the system to return to its initial state without external assistance.

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