Page 1 of 1

### Midterm Q4A

Posted: Sun Feb 25, 2018 9:56 pm
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?

### Re: Midterm Q4A

Posted: Sun Feb 25, 2018 10:16 pm
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!

### Re: Midterm Q4A

Posted: Sat Mar 10, 2018 10:16 pm
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.

### Re: Midterm Q4A

Posted: Sun Mar 11, 2018 11:07 pm
Because the external pressure was constant the process was irreversible, and that equation is for reversible processes.