## Midterm Q4A [ENDORSED]

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

donnanguyen1d
Posts: 64
Joined: Fri Sep 29, 2017 7:04 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 in this question you can assume constant P?

Ishan Saha 1L
Posts: 60
Joined: Fri Sep 29, 2017 7:03 am

### Re: Midterm Q4A

Hi! I also made this same mistake and treated it as though pressure was not constant. The thing is that it is never explicitly states that the system is reversible, or that the external pressure matches the internal pressure. Therefore you can assume that pressure remains constant throughout the process.

Matthew Lin 2C
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: Midterm Q4A  [ENDORSED]

Yes this can be confusing because the problem did not explicitly state whether pressure was constant or not. However, I guessed that it was because it said that the EXTERNAL pressure was 0.5 atm and usually external pressure stays constant.

Jessica Nunez 1I
Posts: 58
Joined: Thu Jul 13, 2017 3:00 am

### Re: Midterm Q4A

As mentioned, the key words, external pressure, helped me identify that pressure is constant.

Emily Glaser 1F
Posts: 156
Joined: Thu Jul 27, 2017 3:01 am

### Re: Midterm Q4A

You can find the internal pressure of the system using the constants you were given. I did that on the test, and I found that the internal pressure of was not the same as the external pressure