Question

Multiple Choice

1) Using the principle of corresponding states, Determine the pressure and temperature of He that corresponds to 5 atm and 300K of Oxygen(gas)

a)	P = 505 kPa T = 90 K
b)	P = 505 kPa T= 20 K
c)	P= 22.9 kPa, T = 10 K
d)	P = 229 kPa T = 90 K

2)Calculate how many seconds a heating coil must run with a current of 3.2 A at 14.5V if 10% of the total work performed on the coil was transfered as heat to an expansion of an ideal gas with Vf=85L and Vi=20L at an external pressure of 2.5 bar.

a) 0.24 s

b) 3500 s

c) 250 s

d) 750 s

Answer 1

Ans 1

Law of corresponding states

At the same reduced temperature and reduced pressure, the compressibility factor also remains the same for real gases.

reduced temperature

Tr = T/Tc

Reduced pressure

Pr = P/Pc

For Oxygen gas

T = temperature = 300 K

P = pressure = 5 atm

c subscript represents critical point

For oxygen

Tc = 154.58 K

Pc = 50.768 atm

Tr = 300/154.58 = 1.9407

Pr = 5/50.768 = 0.0984

For helium

Tc = 5.1950 K

Pc = 2.2452 bar

At the same reduced properties

T = Tr x Tc

= 1.9407 x 5.1950

= 10.08 K

P = Pr x Pc = 0.0984 x 2.2452

= 0.2209 atm x 101.325 kPa/atm

= 22.38 kPa

Option C is the correct answer