Entropy Variation - System, Neighborhood and Universe

Thread starter jaumzaum
Start date Mar 18, 2013
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Entropy System Universe Variation

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The discussion centers on the concept of entropy change in thermodynamic processes, specifically the equation ΔSuniv = ΔSsys + ΔSneib. It highlights that when ΔSuniv is greater than zero, the process is spontaneous. A key point of confusion arises regarding the relationship between heat transfer and entropy, particularly the equation ΔS = Q/T, which applies only to reversible processes. It is clarified that for irreversible processes, the entropy change is greater than Q/T, leading to the conclusion that ΔSuniv cannot always equal zero, as the heat exchanged between the system and its surroundings is not simply equal and opposite. This distinction is crucial for understanding the spontaneity of processes in thermodynamics.

Mar 18, 2013

jaumzaum

I learned ΔS_univ = ΔS_sys + ΔS_neib

If ΔS_univ > 0 the process is spontaneous.

But ΔS = Q/T right? Shouldn't Q_sys = -Q_neib? (The heat released by the system = - heat released by the neighborhood)
I cannot understand why this is wrong!

If it were the case, ΔS_univ would be always zero

Can anyone help me?

[]`s
John

Chemistry news on Phys.org

Mar 18, 2013

DrDu

Science Advisor

##\Delta S=Q/T## only for reversible processes.For irreversible processes, ##\Delta S>Q/T##.

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