Variables in reversible isothermal vs isolated system  [ENDORSED]

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Lucia H 2L
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Variables in reversible isothermal vs isolated system

Postby Lucia H 2L » Wed Feb 14, 2018 2:58 pm

What exactly are all of the values that equal zero in an isolated system (or bomb calorimeter) vs in a reversible isothermal system?

I know that:

isolated
w = 0

reversible
deltaH = 0
deltaU = 0
w = 0?

what happens to q, and delta S, in these? /anything else important that I am forgetting?

Anna Goldberg 2I
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Re: Variables in reversible isothermal vs isolated system

Postby Anna Goldberg 2I » Wed Feb 14, 2018 3:17 pm

q reversible=-w
And delta S should equal zero for reversible.

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Re: Variables in reversible isothermal vs isolated system  [ENDORSED]

Postby Chem_Mod » Wed Feb 14, 2018 3:22 pm

The qtot = qsys + qsurr = 0 for an isolated system.

For a reversible, isothermal system work is most definitely not 0. Recall the expression w = -nRTln(V2/V1) for an isothermal reversible process. Also, q is +nRTln(V2/V1) for isothermal reversible so that q + w = ΔU = 0.

You would calculate entropy changes for each system using ΔSsys = qrev/T. For the isolated system, this all depends on the value of qsys. In an isothermal reversible system it is ΔS = nRln(V2/V1).

Note that only ΔStot = 0 for reversible processes. ΔSsys can still take on a nonzero value.


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