Thermodynamics Questions and Answers – Pure Substance

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Pure Substance”.

1. Which of the following represents the specific volume during phase transition.
a) Vf-Vg
b) Vg-Vf
c) Vf+Vg
d) none of the mentioned
View Answer

Answer: b
Explanation: Here Vg is the specific volume of the saturated vapour and Vf is the specific volume of the saturated liquid.
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2. At critical point, value of Vg-Vf is
a) two
b) one
c) zero
d) infinity
View Answer

Answer: c
Explanation: As pressure increases, there is a decrease in Vg-Vf and at critical point its value becomes zero.

3. Above the critical point, the isotherms are continuous curves.
a) true
b) false
View Answer

Answer: a
Explanation: These continuous curves approach equilateral hyperbolas at large volumes and low pressures.
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4. A rigid tank contains 50 kg of saturated liquid water at 90°C. Determine the pressure in the tank and the volume of the tank.
a) 0.0518 m3
b) 0.0618 m3
c) 0.0718 m3
d) 0.0818 m3
View Answer

Answer: a
Explanation: P = [email protected] C = 70.183 kPa
v = [email protected] C = 0.001036 m3/kg
Total volume of the tank = mv = (50kg)( 0.001036 m3/kg)
= 0.0518 m3.

5. A piston –cylinder device contains 0.06m3 of saturated water vapour at 350 kPa pressure. Determine the temperature and mass of the vapour inside the cylinder.
a) 0.104 kg
b) 0.124 kg
c) 0.134 kg
d) 0.114 kg
View Answer

Answer: d
Explanation: T = [email protected] = 138.86°C
v = [email protected] = 0.52422 m3/kg
m = V/v = 0.06 m3/0.52422 m3/kg = 0.114 kg.
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6. A rigid tank contains 10 kg of water at 90°C. If 8 kg of the water is in the liquid form and the rest is in the vapour form, determine the pressure in the tank.
a) 60.183 kPa
b) 70.183 kPa
c) 80.183 kPa
d) 90.183 kPa
View Answer

Answer: b
Explanation: P = [email protected]°C = 70.183 kPa.

7. A rigid tank contains 10 kg of water at 90°C. If 8 kg of the water is in the liquid form and the rest is in the vapour form, determine the volume of the tank.
a) 1.73 m3
b) 2.73 m3
c) 3.73 m3
d) 4.73 m3
View Answer

Answer: d
Explanation: P = [email protected]°C = 70.183 kPa
@ 90°C, vf = 0.001036 m3/kg and vg = 2.3593 m3/kg
V = Vf + Vg = mf vf + mg vg = 4.73 m3.
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8. An 80 litre vessel contains 4 kg of R-134a at a pressure of 160 kPa. Determine the temperature.
a) -10.60°C
b) -13.60°C
c) -15.60°C
d) -19.60°C
View Answer

Answer: c
Explanation: v = V/m = 0.080 m3/4 kg = 0.02 m3/kg
@ 160kPa, vf = 0.0007437 m3/kg; vg = 0.12348 m3/kg
vf < v < vg Therefore T = [email protected] = -15.60°C.

9. An 80 litre vessel contains 4 kg of R-134a at a pressure of 160 kPa. Determine the quality.
a) 0.127
b) 0.137
c) 0.147
d) 0.157
View Answer

Answer: d
Explanation: v = V/m = 0.080 m3/4 kg = 0.02 m3/kg
@ 160kPa, vf = 0.0007437 m3/kg; vg = 0.12348 m3/kg.
vf < v < vg
x = (v –vf)/ vfg = 0.157.
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10. An 80 litre vessel contains 4 kg of R-134a at a pressure of 160 kPa. Determine the volume occupied by the vapour phase.
a) 0.0775 m3
b) 0.0575 m3
c) 0.0975 m3
d) 0.0375 m3
View Answer

Answer: a
Explanation: v = V/m = 0.080 m3/4 kg = 0.02 m3/kg
@ 160kPa, vf = 0.0007437 m3/kg; vg = 0.12348 m3/kg
vf < v < vg
x = (v –vf)/ vfg = 0.157
mg = x*m(total) = 0.628kg
Vg = mg*vg = 0.0775 m3 or 77.5 litre.

11. Determine the specific volume of R-134a at 1 MPa and 50°C, using ideal gas equation of state.
a) 0.022325 m3/kg
b) 0.024325 m3/kg
c) 0.025325 m3/kg
d) 0.026325 m3/kg
View Answer

Answer: b
Explanation: v = RT/P = (0.0815 kJ/kg.K)* (323 K)/(1000 kPa)
= 0.026325 m3/kg.

Sanfoundry Global Education & Learning Series – Thermodynamics.
To practice all areas of Thermodynamics, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter