## Expansion Against a Vacuum

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Michelle Wang 4I
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am

### Expansion Against a Vacuum

How come when a gas expands against a vacuum work = 0? What does delta S, delta U, and q equal for this situation as well?

Gary Qiao 1D
Posts: 66
Joined: Fri Sep 28, 2018 12:26 am

### Re: Expansion Against a Vacuum

When the gas is expanding in a vacuum, there is nothing to oppose the gas (free expansion), making the work = 0. In a vacuum, there is also no change in temperature or heat change, making delta U = 0, thus q= 0. delta S in free expansion would still be equal to nRln(V2/V1).

MackenziePerillo-1L
Posts: 31
Joined: Fri Sep 28, 2018 12:19 am

### Re: Expansion Against a Vacuum

would this be an example of an irreversible system?

Fionna Shue 4L
Posts: 59
Joined: Fri Sep 28, 2018 12:18 am

### Re: Expansion Against a Vacuum

Yes, this would be an irreversible system

Jason Ye 2I
Posts: 33
Joined: Fri Sep 28, 2018 12:22 am

### Re: Expansion Against a Vacuum

Yes that is an irreversible system.