A vertical piston-cylinder device initially contains .2 m^3 of air at 20C. The m

Question

A vertical piston-cylinder device initially contains .2 m^3 of air at 20C. The mass of the piston is such that it maintains a constant pressure of 300kPa inside. Now a valve connected to the cylinder is opened, and air is allowed to escape until the volume inside the cylinder is decreased by one-half. Heat transfer takes place during the process so that the temperature of the air in the cylinder remains constant. Determine a) the amount of air that has left the cylinder and b) the amount of heat transfer

Explanation / Answer

amount of air remaining in cylinder =m= (pv)/(RT) treating air as ideal gas
m=(.357kg)
as half of the gas has left the cylinder
amount remaining in cylinder = amount of gas left the cylinder =.357 kg.
b)
w = pV=300 *.1 =-30 kj

U =m(Cv T)

= -.357(.718 * 293)= -75.05 kj.

Q=U+w =-105.05 kj.

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