## Lecture Diagram

$\Delta S = \frac{q_{rev}}{T}$

Sabrina Fardeheb 2B
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### Lecture Diagram

Can someone please explain the diagram from Wednesday's lecture? It consisted of a vacuum, work being done, external pressure, and heat. Is this a container with a gas? I'm mostly confused as to what's happening and in what system. Thanks!

Salman Azfar 1K
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Joined: Thu Jul 13, 2017 3:00 am

### Re: Lecture Diagram

I'm pretty sure the point was to show gas expanding against a piston with a vaccum being on the other end of the piston. It was just an alternative way to show gas expansion.

Hannah Chew 2A
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### Re: Lecture Diagram

The diagram is of a heat reservoir, meaning that it is always at the same temperature. The ideal gas expands into the vacuum and does work, but to remain at the same temperature, heat is added. When it expands, it pulls up the mass. Delta U is still 0 because q + w = 0, where heat added is equal to work performed. The gas still expands because of an entropy increase, not because of "energetic reasons."