# Homework Help: Work using a P-V Graph

1. Aug 5, 2007

### alexithymia916

1. The problem statement, all variables and given/known data

One mole of gas is initially at a pressure of 3.9 atm, volume of .29 L and has an internal energy equal to 108.1 J. In its final state the gas is at pressure 1 atm and volume .7 L, and its internal energy equals 169 J. (There are 6 different questions using this data).

For the path IAF, calculate the work done on the gas. Answer in units of J

okay well there is a graph to better visualize the problem but i can't exactly draw it out but basically the path IAF makes a right angle (If you start from point I you go down and then right). I is at 3.9 atm and .29 L, A is at 1 atm and .29 L, and F is at 1 atm and .7 L.

2. Relevant equations

Work = Pressure x Change in Volume

3. The attempt at a solution
Well to start it off, there is no work done from I to A so therefore you only need to find the work from point A to F
W from path A to F= (1 atm)(.41 litres)
convertingggg
W=(101300 N/m^2)(.00041 m^3)
so you should get
41.533 N*m
so
41.533 J

and somehow when i submit that in, it comes at as wrong... help? :uhh:

2. Aug 6, 2007

### Andrew Mason

It is asking for the work done ON the gas. Is the gas doing work or is work being done on it here?

AM

3. Aug 6, 2007

### alexithymia916

okay so if it's work being done on the gas.. then the equation should be
Change in Internal energy = Q-W
but you don't have specific heat or final or initial temperature..

4. Aug 6, 2007

### Andrew Mason

When gas expands, it DOES work. So in this case, it DOES work, so the work DONE ON the gas is negative. Just put a - sign in front of your answer.

AM

5. Aug 6, 2007

### alexithymia916

oh geeeez
pardon my ignorance...
thanks so much :)