Change in Entropy of surroundings for irreversible process

AI Thread Summary
The equation ΔSsurroundings = -Qirr/T is valid for irreversible processes because it assumes the surroundings act as a thermal reservoir, maintaining a constant temperature during heat exchange. This condition allows for the calculation of entropy change using the reversible process equation, despite the irreversibility of the system itself. The uniform temperature of the reservoir ensures that there are no significant temperature gradients, which could complicate the analysis. Additionally, using a mixture of liquid and solid at the melting point can help achieve this uniformity in real-world scenarios. Thus, the approach effectively simplifies the analysis of entropy changes in irreversible processes.
dhtikna
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Homework Statement


I know that the equation ΔSsystem = Q/T is only valid for a reversible process but whenever i see problems involving a irreversible isothermal expansion of ideal gas, the ΔSsurroundings is taken as -Qirr/T. Why is that equation valid for surroundings, is it because the surroundings being a reservoir/sink, any heat exchange is done reversibly?


Homework Equations



ΔSsystem = Q/T
 
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dhtikna said:

Homework Statement


I know that the equation ΔSsystem = Q/T is only valid for a reversible process but whenever i see problems involving a irreversible isothermal expansion of ideal gas, the ΔSsurroundings is taken as -Qirr/T. Why is that equation valid for surroundings, is it because the surroundings being a reservoir/sink, any heat exchange is done reversibly?


Homework Equations



ΔSsystem = Q/T
This assumes that there are no significant temperature gradients present within the reservoir (so that the temperature of the entire reservoir is uniform) and that the reservoir temperature remains constant during the process. This can be approached in the real world by having the material in the reservoir consist of a mixture of liquid and solid at the melting point.

Chet
 

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