## Midterm Q4A

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

Yea Eun Lee 1H
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Midterm Q4A

A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and
undergoes an expansion against 0.5 atm external pressure until its volume doubles.
Calculate the work involved in Joules.

How come for this problem we don't use the equation -nRT ln V2/V1?

Kyle Sheu 1C
Posts: 87
Joined: Fri Jun 23, 2017 11:39 am

### Re: Midterm Q4A

That would be because the -nRTlnV2/V1 equation is used for reversible, isothermal expansion; because the problem describes expansion against a constant, external pressure of 0.5 atm, we'd use w = -PexdeltaV

Hope this helps!

lizzygaines1D
Posts: 52
Joined: Thu Jul 13, 2017 3:00 am

### Re: Midterm Q4A

yeah just to add on and clarify because this problem was tricky and there was info given that you didn't need. the external pressure never changed throughout the reaction.

Mishta Stanislaus 1H
Posts: 45
Joined: Fri Sep 29, 2017 7:04 am

### Re: Midterm Q4A

Because the external pressure was constant the process was irreversible, and that equation is for reversible processes.