# Thermodynamics - Energy analysis of piston-cylinder device

1. Sep 25, 2007

### eh87

Hello :)

I'm having trouble working on this homework question (please see attachment). The answers are supposed to be
a) 22.61 KJ
b) 36.79 KJ
c) 151.8*C

I solved (a) and I noticed that the answer to (c) is that saturation temperature at 500kPa, but I just cannot get (b)! In fact, I'm not really sure I even know what's given for part (b). Obviously P=500kPa, but what else is known? Would Vb = 0.6(Va) = 0.0551898 m^3 ? It seems like I need another intensive property (other than P) to identify the state as a start.

help

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2. Sep 25, 2007

### eh87

3. Sep 25, 2007

### eh87

So I worked on it some more, just trying to understand the darn thing.. and yes, $$V_{b}$$ = 0.0551898 m^3. Now which formula to use for boundary work?

For constant temp and an ideal gas, I know the formula:
$$W_{b}$$ = $$\int$$$$mRT/V$$dV = mRT*ln($$V_{2}$$/$$V_{1}$$)

But prof said that for real gases undergoing an isothermal process, the integral in the boundary work equation "would be done numerically." What does that mean??