Pure Substances Sample Exercise

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TUTORIAL CHAPTER 2
(PART 2)
QUESTION 1
A tank has a volume of 0.5m3 and contains 10 kg of
an ideal gas having a molecular weight of 24
kg/kmol. The temperature is 25oC. What is the
pressure?
(Ans: P=2065 kPa )
QUESTION 2
The pressure in an automobile tyre depends on the
temperature of the air in the tyre. When the air is
25oC, the pressure gauge reads 210 kPa. If the volume
of the tyre is 0.025m3, determine the pressure rise in
the tyre when the air temperature in the tyre rises to
50oC. Also, determine the amount of air that must be
bled off to restore pressure to its original value at this
temperature. Assume the atmosphere pressure is 100
kPa.
(Ans: P= 26 kPa, m=0.0070 kg )
QUESTION 3
A 1m3 tank containing air at 25oC and 500kPa is
connected through a valve to another tank
containing 5kg of air at 35oC and 200 kPa. Now
the valve is opened and the entire system is
allowed to reach thermal equilibrium with the
surroundings, which are at 20oC. Determine:
a) the volume of the second tank
b) the total mass in both tanks
c) the final equilibrium pressure of air
(Ans: V2 = 2.211 m3, mt=5.843 kg, Pf=284.1 kPa )
QUESTION 4
Ethane in a rigid vessel is to be heated from
350kPa and 40oC until its temperature is 315oC.
What is the specific volume and final pressure of
the ethane as predicted by compressibility chart?
(Ans: P = 671 kPa)
QUESTION 5
A 0.016773 m3 tank contains 1 kg of refrigerant-134a at
110°C. Determine the pressure of the refrigerant, using
(a) the ideal-gas equation
(b) the generalized compressibility
(c) the refrigerant tables.
Ans: (a) 1.861 MPa, (b) 1.603 MPa, (c) 1.6 MPa
6
QUESTION 6
A 1m3 tank contains 2.841 kg of steam at 0.6 MPa.
Determine the temperature of the steam, using
(a) the ideal gas equation
(b) the van der Waals equation
(c) the steam tables.
Ans: (a) 457.6 K, (b) 465.9 K, (c) 473 K
QUESTION 7
A 3.27 m3 tank contains 100 kg of nitrogen at 175 K.
Determine the pressure in the tank, using
(a) the ideal-gas equation
(b) the van der Waals equation
(c) the Beattie-Bridgeman equation
Compare your results with the actual value of 1505 kPa.
Ans: (a) P=1588 kPa (5.5% error), (b) P= 1495 kPa (0.7% error),
(c) P=1504 kPa (0.7%)
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