Isobaric compression from isotherm to adiabat

[nlingraham]

Homework Statement

The figure(Figure 1) shows a thermodynamic process followed by 150 mg of helium. Determine the pressure (in atm) at points 1, 2, and 3. Determine the temperature (in °C) at points 1, 2, and 3.

http://imgur.com/B7lwQ

n=.0375 mol
P₁=3 atm
P₂=1 atm
T₁=971.85 k
T₂=971.85 k
V₁=1000 cm^3
V₂=V₃=3000 cm^3

Homework Equations

PV=nRT

The Attempt at a Solution

I'm only on the pressure part right now. From the given chart P₁=3 atm. I used PV=nRT, and got that T₁ and T₂ are 971.85 K. With that, I used ideal gas law again to get that P₂=1 atm. However, I don't know how to get the pressure at point 3 since I don't know the temperature at that point. It looks like it goes through an isobaric compression from the isotherm to the adiabat to me. Any help is appreciated.

(303000)(.001)=(.0375)(8.314)T, T₁=T₂=971.85 K

P(.003)=(.0375)(8.314)(971.85), P₂=1 atm

 

[rock.freak667]

From 1 to 3, the He goes through an adiabatic process such that

PV^γ= constant

So you will have to use this to get P₃

 

[nlingraham]

Ok, I get the PV^γ, where γ=5/3 since its a monatomic gas, but what exactly is the constant? Is that supposed to be nR?

 

[nlingraham]

Ok, I think I got it. So it would be P₂V₂^γ=P₁V₁^γ and then just solve for P₂

 

[nlingraham]

Thank you for your help!