Oxygen cylinder at pressure of 500 atm is kept at a temperat

Oxygen cylinder at pressure of 500 atm is kept at a temperature of -150 degree C. Is the oxygen in the cylinder an ideal gas? If not, how much its enthalpy and entropy deviates from ideal gas?

Solution

Given pressure, P = 500 atm = 500 × 101.325 kPa = 50662.5 kPa.

Temperature = -150°F = -101.11°C = 171.89 K.

Compression Factor, z = PV/RT.

R for Oxygen = 8.314/32 = 0.2598 kJ/kg-K

For ideal gas, z=1, so V = RT/P = 0.2598 × 171.89/50662.5 = 8.815 × 10^(-4).

= 881.5 cm^3. Which will be very small size cylinder where ideal gas equation will be valid. So, no need to deviate enthalpy and entropy equation from ideal gas equation.