How Do You Calculate Work and Internal Energy from a Thermodynamic Graph?

[ice87]

http://noether.physics.ubc.ca/physics153/assign52k5.pdf

number 3. For part d I'm finding the work by looking at the area under the graph, and a friend of mine used 1.5kdT, which also seems to make sense in this situation, but we're getting 2 different answers. For the change in internal energy and the heat taken in i know that all i need to do is find one of them and the other one comes easily but I have no idea how to find either one.

 

[Skippy]

What's the change in Internal energy for a cyclic process?
What's the change in Internal energy for an isotherm?

Both of those are givens, that you don't need to calculate. Then you should be able to see what the change in energy is for the line you're looking at.

Area under the graph should be right. Length * 1.5 (for the height), which I think that's what you were saying...

 

[GCT]

You may be looking for the change in enthalpy, the curve seems to represent a irreversible process, thus the mechanical work done on the system is the area under the straight line. The work will contribute to the change in internal energy and and some of it will be wasted RTdn+RndT. From the difference, the dU can be calculated.

I assumed that the maximum temperature was at V2.

btw, I assumed a lot of things in that I tried to solve it by conceptual means, when really I should have worked out the math. So I would wait for more advice.