Thermodynamics help required?

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

(i) the characteristic gas constant of oxygen in kj/kgK.

(ii)the mass of oxygen in the piston-cylinder apperatus

(iii) the pressure of oxygen after process 1

(iv) the pressure of oxygen after process 2

(v) the temperature of oxygen after process 3

Best answer will be awarded.

Let&#39;slearntothink · Accepted Answer

(i) the characteristic gas constant of oxygen in kj/kgK.
Required Constant = 8.314/32 = 0.260 kJ/(kgK)

(ii)the mass of oxygen in the piston-cylinder apparatus
No of moles of oxygen= [{2.5*(10^5)*0.3}/293]/8.314 = 30.788 
Mass of oxygen = (30.788*32)/1000 kg = 0.985 kg
 

(iii) the pressure of oxygen after process 1 = 2.5*(393/293) = 3.353 bar


(iv) the pressure of oxygen after process 2 = 2.5*(0.3/0.5)^1.4 = 1.223 bar
and temperature, T2 will be 393*(0.3/0.5)^0.4 = 320.37 K

(v) the temperature of oxygen after process 3 = 320.37*(0.4/0.5) = 256.3 K
or - 16.70 degree Celsius

Thermodynamics help required?

1 Answer