Chemical Engineering Thermodynamics (CL 253)

Mid-semester Examination (2012)

1. 1.0kgmole of nitrogen gas a 1.0 bar and 300K, in a closed piston and cylinder arrangement is

compressed isothermally. During the process the internal energy increases by 24kJ while 28kJ of

heat leaves the system. Find the final system pressure (in bar) assuming that the gas obeys the

second-order virial EOS. (Tc = 126.2K; Pc = 34.0bar; ω = 0.038). (Ans: 8.0bar)

2. An ideal gas discharges from a perfectly insulated tank initially at 300C and 5 bar. Compute the

temperature and pressure of the gas in the cylinder when 50% (by weight) of the gas has been

discharged. Assume that for the gas1.5.γ = Derive all expressions you need to use. (Ans: 214K,

1.76bar)

3. A rigid tank (volume 1.0m3) contains a certain gas ‘A’ that is stored at a temperature of 4000K. The

pressure in the tank at this temperature is 10 bar. The tank is brought near a high temperature

furnace, and its pressure doubles due to heating. Compute (a) the final gas temperature in the tank;

(b) the amount of heat transferred (in kJ) to the contents of the tank during the process of heating.

The EOS followed by the gas is: (PV/RT) = 1 – 0.4 (Pr/Tr2); average C

Pig /R = 4.0; Pc = 50 bar, Tc =

8000K, ω = 0.1, PAsat (at 4000K) = 12bar. (Ans: 3102.6kJ)

4. A gas passes through the system shown in figure below under steady state conditions:

Porus plug

Compression device

Initially at 40bar and 600K the gas first seeps through a porus plug whereupon its pressure drops

to 1 bar. Next the gas stream is isothermally compressed by application of 5000J/mol of work to

attain a pressure of 20bar at the exit of the compression device. Compute the amount of heat per

mole of gas (in kJ) that needs to taken out of the compression device in order to ensure an

isothermal compression process. The pipeline is perfectly insulated till the entry point to the

compression device. The EOS for the gas is: ;RT

VP RT

β= + where 3 24.6 . / .J m molβ = − Also,

0( ) 32.0 / ; 500 ; 40 ; 0.05.P c cC average J mol K T K P barω= = = = (Ans: 12.0kJ/mol)