# Thermodynamics - PV diagram

1. Apr 21, 2012

### atsum

The question is to calculate: q, w, ∆U, ∆H, ∆S for each step(A to B, B to C, C to A)

I know how to calculate the values on figure 1, but, how to calculate A to B on figure 2?

For A to B on figure 1, it is isothermal process, therefore, I can easy to find out the answer, but I don't know what is the process for A to B on figure 2.

Can anyone tell me what the condition difference (A to B) between figure 1 and 2?

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2. Apr 22, 2012

### Psi^2

Hello.

You don't need to know what kind of process is between A and B on picture 2. You simply calculate work by integrating, or simpler, by calculating surface under the AB line. It is easy to calculate, because you have one right angled triangle and one rectangle. (i will do approximation: 1atm=10^5 Pa, a 1L=1dm^3=10^-3 m^3)

Surface of triangle is:

S(t)=\frac{pV}{2}=\frac{5*10^{5}Pa*4*10^{-3}m^{3}}{2}=1000J

Surface of rectangle is:

S(r)=pV=10^{5}Pa*4*10^{-3}m=400J

So, total work is W=S(t)+S(r)=1400J

And now you can calculate everything else.

3. Apr 22, 2012

### Psi^2

P.S. I have some technical issues here.. you can copy these formula code into this application, and you will see it: http://www.codecogs.com/latex/eqneditor.php