Thermodynamics physics help?

Question

Oxygen trapped inside an insulated smooth piston-cylinder apparatus has a volume of 0.3m^3, pressure of 2.5bar and tempreture of 20 degree C. It is then subjected to the following thermodynamic processes sequentially:

Process 1: heating under constan tvolume condition until its temperature increases to 120 degree C

Process 2: Undergo polytropic expansion where PV^1.4 = constant, until its volume increases to 0.5m^3

Process 3: Cooling under constant pressure condition until its volume decreases to 0.4m^3

Assuming:

Universal gas constant = 8.314kJ/kmol.K, and
Molar mass of oxygen molecule = 32kg/kmol

Determine:
The pressure of oxygen after process 2.
a) 1.64 bar
b) 1.22 bar
c) none of above

Can you please show your work.

Best answer awarded.

Anonymous · Accepted Answer

if PV^1.4 is a constant then no matter what the P and V is at any point in time, PV^1.4 is constant. Find out what the constant is by knowing the unknowns P and V:
2.5*0.3^1.4= k (I don't have a calculator so plug it in)
then:
P*0.5^1.4= the same k you got before and solve for P :)

Thermodynamics physics help?

1 Answer