An insulated vertical cylindrical vessel of cross-sectional area A= .12m^2 contains 20 mol of He gas at To= 300K and Po= .5 bar. It is capped by a movable piston of mass m = 150kg supported from the ceiling by a wire. The top of the vessel is open to the atmosphere (Patm = 1bar, Tatm = 300K). The wire is cut and the weight falls and compresses the gas.
a) Obtain the pressure and temperature of gas a short time after the wire has been cut, when a negligible amount of heat transfer has taken place.
b)After a long time, the He gas thermally equilibrates with the enviornment by heat transfer through the piston. How much heat is exchanged with the environment during this process?
Helium can be considered to be an ideal gas at all conditions of interest, with Cv= 3*R/2
Not sure.....There are so many I don't know which to use. I'm guessing:
delta U =n*Cv*delta(T) <------from my thermo textbook
Work= integral for force times displacement
also Pf= Ppiston + Patmosphere
The Attempt at a Solutionfor part a):
F= 9.8 m/s^2 *(150 kg) = 1,470 N
P=F/A----> 1,470 N/0.12 m2 =12,250 Pa
I know the above is a calculation I will have to make, but I'm not sure what else to do from here. This is neither a constant pressure or constant volume process, so I don't know why I'm given Cv.
Confused...Please help. :/