## Thermodynamics Interview Questions [99+] For Mechanical Engineering Student

• • June 16, 2021

Thermodynamics Interview Questions: Here In This Post We Will learn Important Term & Definition of Thermodynamics for Interview or Competition Exam. [Thermodynamics Interview Questions]

## What is Thermodynamics? ( Interview Question )

The thermodynamic is that branch of Engineering – Science which deals with the energies possessed by gases and vapors. It also includes the conversion of these energies in terms of heat and mechanical work and their relationship with properties of the system.

## Objective Type Questions

### Q.1 Define Thermodynamic System? (#Interview Question)

A definite area or a space where some thermodynamic process takes place is known as thermodynamic system.

### Q.2 Explain the following terms

1. 1. Open System
2. 2. Closed System
3. 3. Isolated System

:- Open System :- An open system is one in which both the heat and work as well as mass of the working substance crosses the boundary of the system.For example: A reaction taking place in an open vessel exchanges both energy and matter with the surrounding.

:- Closed System :- A closed system is one in which heat and work crosses the boundary of the system but the mass of the working substances does not crosses the boundary of the system.For example: A reaction taking place in a closed metallic vessel.

:- Isolated System :- In an isolated system, neither the heat and work nor the mass of the working substance crosses the boundary of the system. For example: Water placed in a vessel that is closed as well as insulated.

### Q.3 Explain the Laws of Thermodynamics?

Zeroth Laws of Thermodynamics :- Zeroth laws of thermodynamic states that when two bodies are in thermal equilibrium with third body then they are also thermal equilibrium with each other.

First Laws of Thermodynamics :- First law of thermodynamic states that energy can neither be created nor be destroyed but it can be transform from one form to another form.

Second Law of Thermodynamics:- This law states that “all processes in nature tend to occur with an increase in entropy and the direction of change always lead to the increase in entropy.”

This law states that there is a definite limit to the amount of mechanical energy, which can be obtained from a given quantity of heat energy.

or

Second Laws of Thermodynamics has two statements:-

According to Claussius, this law may be stated as “It is impossible for a self acting machine working on cyclic process, to transfer heat from a body at a lower temperature to a body at a higher temperature without the aid of an external agency”

The second law of thermodynamics has also been stated by Kelvin-Planck as “It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy to work.” According to this statement, the second law of thermodynamics is sometimes called as law of degradation of energy.

Third Law of Thermodynamics:- The value of entropy of a completely pure crystalline substance is zero at absolute zero temperature.

## Q.4 State The Third Law Of Thermodynamics. Give Its Limitations And Importance.? (#Thermodhynamic Interview Question)

Third Law of Thermodynamics States That : –

“The entropy of a perfect crystal of each element and a compound is zero at absolute zero.”

Limitations: If any disorder like impurity or imperfection is found in a substance then the entropy of such crystal is non-zero at 0 K. For example: The entropy of pure carbon dioxide and nitric oxide is zero at 0K. This shows that there exists disorder in the arrangement of such molecules.

This law is applicable only to pure compounds. Thus we can say that, this law is not applicable to glass which is a supercooled liquid. It is also not applicable to amorphous substance and supercooled solutions.

Importance:

• With the help of this law Thermodynamic properties can be calculated and chemical affinity can be measured.
• This law helps in explaining the behaviour of solids at very low temperature.

### Q.5 Define the following terms?

1. 1. Extensive Properties:- The properties of the system, whose value for the entire system is equal to the sum of their values for the individual parts of the system, are called extensive properties. For example, total volume, total mass, & total energy.
2. 2. Intensive Properties:- The properties of the system, whose value for entire system is not equal to the sum of their values for the individual parts of the system, are called intensive properties. For example, temperature, pressure, & density.

### Q.6 When A Real Gas Behaves Like Ideal Gas?

A real gas behaves like a ideal gas at low pressure and high temperature condition.

### Q.7 State the law of Conservation of Energy?

According to law of conservation, “Energy can neither be created nor be destroyed but it can be transformed from one form to another form.”

### Q.8 What is Carnot Engine?

It was being designed by Carnot and let me tell you that Carnot engine is an imaginary engine which follows the Carnot cycle and provides 100% efficiency.

### Q.9 Which Has More Efficiency Diesel Engine Or Petrol Engines?

Diesel Engine is more efficient than Petrol Engine.

### Q.10 Define perfect gas?

The state of substance whose evaporation from its liquid state is complete, is known as perfect gas.

### Q.11 Explain the Laws of Perfect Gases? (#Thermodynamic Interview Question)

:- Perfect Gas :- A perfect gas may be defined as a state of a substance, whose evaporation from its liquid state is complete. It may be noted that if its evaporation is partial, the substance is vapour.

The behavior of superheated vapours is similar to that of a perfect gas.

The physical properties of a gas are controlled by the following three variables:- 1) Pressure exerted by the gas, 2) Volume occupied by the gas, and 3) Temperature of the gas.

Laws of Perfect Gas:-

1. 1. Boyle’s Law:-
2. This law was formulated by Robert Boyle in 1662. It states, “The absolute pressure of a given mass of a perfect gas varies inversely as its volume when the temperature remains constant.”

2. Charles Law :-

This law was formulated by Frenchman Jacques A.C. Charles in about 1787. It may be stated in two different forms.

(i) “The volume of a given mass of a perfect gas varies directly as its absolute temperature, when the absolute pressure remain constant.”

(ii) “All perfect gases change in volume by 1/273 th of its original volume at 0 degree Celsius for every 1 degree Celsius change in temperature, when pressure remain constant.”

3. Gay – Lussac Law:- This law states, “The absolute pressure of a given mass of a perfect gas varies directly as its absolute temperature, when the volume remains constant.”

### Q.12 What do you understand by the Macroscopic & Microscopic approach of thermodynamics?

While macroscopic is concern with certain quantity of matter and its behaviour, microscopic approach deals with molecular and atomic behaviour of matter and energy.

### Q.13 Define reversible process?

Reversible process is one in which both the system and the surroundings are returned to their original states, which is not so in the case of irreversible process. In actual practice, all processes are irreversible.

Adiabatic process is one in which there is no flow of heat between a system and its surroundings.

## Q. 15 What do you understand from Exergy and Anergy?

Exergy (Available Energy) can be converted into work but Anergy (Unavailable Energy) can not be converted to work.

## Q. 15 Explain Carnot Cycle?

The Carnot cycle is a theoretical ideal thermodynamic cycle proposed by French physicist Nicolas Léonard Sadi Carnot in 1824 and expanded upon by others over the next few decades.

The four stages in the Carnot cycle. (A) Stage 1: Isothermal expansion under heat input Q1, (B) Stage 2: Adiabatic expansion accompanied by a fall in temperature T1 to T2, (C) Stage 3: Isothermal compression, Q2 exhausted, (D) Stage 4: Adiabatic compression accompanied by an increase in temperature T2 to T1.

### Q.16 Define Enthalpy?

When a process takes place at constant pressure, the heat absorbed or released is equal to the Enthalpy change. Enthalpy is sometimes known as “heat content”, but “enthalpy” is an interesting and unusual word, so most people like to use it. Etymologically, the word “entropy” is derived from the Greek, meaning “turning” and “enthalpy” is derived from the Greek meaning “warming”. As for pronunciation, Entropy is usually stressed on its first syllable, while enthalpy is usually stressed on the second.

Enthalpy(H) is the sum of the internal energy(U) and the product of pressure(P) and volume(V).

Enthalpy H can be written as,

H = U + pV

Where, H = Enthalpy of the system

U = Internal energy of the system

p = Pressure of the system

V = Volume of the system

Enthalpy is not measured directly, however, the change in enthalpy (ΔH) is measured, which is the heat added or lost by the system. It is entirely dependent on the state functions T, p and U.

### Q.17 Define Heat?

Energy in transition flowing by virtue of temperature difference from one system to other when two are in contact called Heat.

### Q.18 Define Specific Heat?

Specific heat is the heat required by 1 unit mass of substance to raise the temperature by one degree.

### Q.19 Difference between first & second laws of thermodynamics.

First law is concerned with quantity and sum total of energy but second law accounts for quality, availability, reversibility, losses, efficiency etc. It explains the difference between heat and work, exergy and anergy.

### Q. 20 Difference between Enthalpy and Entropy?

Thermodynamics Interview Questions

## OBJECTIVE TYPE QUESTION: Interview Questions

1. 1. A definite area or space where some thermodynamic process takes place is known as
2. a) Thermodynamic System
3. b) Thermodynamic Cycle
4. c) Thermodynamic Process
5. d) Thermodynamic Law

2. A closed system is one in which heat and work crosses the boundary of the system but the mass of the working substance does not crosses the boundary of the system.

a) Yes

b) No

3. An open system is one in which both the heat and work as well as mass of the working substance crosses the boundary of the system. (Yes/No)

Yes

4. In an isolated system, neither the heat and work nor the mass of the working substance crosses the boundary of the system. (True/False)

True

5. The thermodynamic property of a system is said to be an intensive property whose value for the entire system __________ the sum of their value for the individual parts of the system.

a) is equal to

b) is not equal to

6. The property of the system, whose value for the entire system is equal to the sum of their values for the individual parts of the system is called extensive property. (True/False)

True

7. The absolute zero temperature is taken as

a) -273 C b) 273 C c) 237 C d) -237 C

a) – 273.15 C or 0K

8. Which of the following is correct?

• a) Absolute pressure = Gauge pressure + Atmospheric Pressure
• b) Gauge pressure = Absolute pressure + Atmospheric Pressure
• c) Atmospheric Pressure = Absolute pressure + Gauge Pressure
• d) Absolute Pressure = Gauge Pressure – Atmospheric Pressure

9. The standard value of atmospheric pressure taken at sea level is

• a) 1.013 bar
• b) 760 mm of Hg
• c) 1013 x 102 N/m2
• d) All of these

10. The specific heat of water is 4.187 (True/False)

True

11. When two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This statement is called

• a) Zeroth law of thermodynamics
• b) First law of thermodynamics
• c) Second law of thermodynamics
• d) Kelvin Planck’s law

12. First law of thermodynamics deals with

• conservation of heat
• conservation of momentum
• conservation of mass
• conservation of energy

13. Energy can neither be created nor destroyed, but it can be transformed from one form to another. This statement is known as

• Zeroth law of thermodynamics
• First law of thermodynamics
• Second law of thermodynamics
• Kinetic theory of gases

14. The heat and work are mutually convertible. This statement is called________ law of thermodynamics.

a) Zeroth b) First c) Second

15. According to Clausis Statement of second law of thermodynamics: It is impossible to transfer heat from a body at a lower temperature to a body at a higher temperature, without the aid of an external source. (True/False)

True

16. According to Kelvin-Planck’s statement of second law of thermodynamic, It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work. (True / False)

True

17. Second law of thermodynamic define

• heat
• work
• internal energy
• entropy

18. The state of a substance whose evaporation from its liquid state is complete, is known as

• vapour
• perfect gas
• air
• steam

19. The behavior of super heated vapour is similar to that of perfect gas (True/False)

True

20. The absolute pressure of given mass of perfect gas varies inversely as its volume, when the temperature remains constant. This statement is known as Boyl’s Law (Yes/No)

Yes

21. As per Charles’ law,Volume of the given mass of perfect gas varies directly as its absolute temperature, when the absolute pressure remains constant. (Yes/No)

Yes

22. According to Gay-Lussac law, the absolute pressure of a given mass of a perfect gas varies directly as its absolute temperature, when the volume remain constant. (True/False)

True

23. Equal volume of all the gases at the same temperature and pressure, equal number of molecules. This statement is called Avogadro’s law. (True/False)

True

24. The temperature at which the volume of a gas becomes zero is called absolute zero temperature. (Yes/No)

Yes

25. The absolute zero pressure will be

• when the molecular momentum of the system becomes zero
• at sea level
• at the temperature of -273K
• at the center of the earth

Thermodynamics Interview Questions

26. Joule’s law state that change of internal energy of a perfect gas is directly proportional to the change of temperature. (Yes/No)

Yes

27. Charles’ law states that all perfect gases change in volume by…………… of its original volume at 0C for every 1C change in temperature when pressure remains constant.

i) 1/27th ii) 1/93th iii) 1/173th iv) 1/273th

28. The general gas equation is pv = mRT where p = pressure, v = volume , T = Absolute temperature, and R = Gas constant. (True / False )

True

29. According to Avogadro’s law, the density of any two gases is …………….. their molecular masses it the gases are at the same temperature and pressure.

1. i) equal to
2. ii) directly proportional to
3. iii) inversely proportional to

30. Universal gas constant (or molar constant) of a gas is the product of molecular mass of the gas and the gas constant. Ru = M R

Where M= Molar Mass & R = Gas constant

True

31. The amount of heat required to raise the temperature of unit mass of a gas through one degree at constant pressure is called specific heat at constant pressure (yes/no)

Yes

32. The amount of heat required to raise the temperature of unit mass of a gas through one degree at constant volume is called specific heat at constant volume. (Yes/No)

Yes

33. The value of specific heat at constant pressure (Cp = 1.005) is ………… that of at constant volume (Cv = 0.717).

i) less than ii) equal to iii) More than

34. The amount of heat required to raise the temperature of 1000g water through one degree is called Kilojoule. (True/False)

True

35. The sum of internal energy (U) and the product of pressure and volume (p.v) is known as …..

1. i) work done
2. ii) entropy
3. iii) enthalpy
4. iv) non of the above

36. According to Regnault’s law, the specific heat at constant pressure (Cp) and specific heat at constant volume (Cv ) doesn’t change with the change in pressure and the temperature of the gas. (True/False)

True

37. When a system changes its state form one equilibrium state to another equilibrium state, then path of successive sates through which the system has passed, is known as

1. i) thermodynamic law
2. ii) thermodynamic system
3. iii) thermodynamic cycle
4. iv) None of these

38. The heat energy stored in the gas and used for raising the temperature of the gas is known as

1. i) external energy
2. ii) internal energy
3. iii) kinetic energy
4. iv) molecular energy

39. When gas is heated at constant pressure, the heat supplied is utilised in

1. i) increasing the internal energy of the gas
2. ii) doing some external work
3. iii) increasing the internal energy of gas and also for doing some external work
4. iv) none of the above

40. A process, in which the temperature of the working substance remains constant during expansion or compression, is called

1. a) isothermal process
2. b) hyperbolic process
4. d) polytropic process

41. A process, in which the gas is heated or expanded in such a way that product of its pressure and volume remains constant, is called isothermal process (Yes/No)

No (is called Hyperbolic Process)

42. A process, in which the working substance neither receives nor gives out heat to its surroundings during its expansion or compression, is called

1. i) isothermal process
2. ii) hyperbolic process
3. iii) adiabatic process or isentropic process
4. iv) polytropic process

43. The free expansion process is a constant enthalpy process. (Correct/Incorrect)

Correct

44. The work done in a free expansion process is zero (True/False)

True

45. The property of a working substance which increases or decreases as the heat is supplied or removed in a reversible manner, is known as

1. a) enthalpy
2. b) internal energy
3. c) entropy
4. d) external energy

46. The entropy of water at 0 .C is assumed to be

1. i) 1 ii) 0 iii) -1 iv) 10

47. The increase in entropy of a system represents

1. a) increase in the availability of energy
2. b) increase in temperature
3. c) decrease in pressure

48. A series of operations, which takes place in a certain order and restore the initial conditions at the end, is known as

1. a) reversible cycle
2. b) irreversible cycle
3. c) thermodynamic cycle
4. d) none of these

49. The main cause for the irreversibility is

1. a) mechanical and fluid friction
2. b) unrestricted expansion
3. c) heat transfer with a finite temperature difference
4. d) all of the above

50. The throttling process is …………. process.

1. a) reversible b)irreversible c) reversible or irreversible

Thermodynamics Interview Questions

51. Carnot cycle consists of

• a) two constant volume and two isentropic processes.
• b) two isothermal and two isentropic processes.
• c) two constant pressure and two isentropic processes
• d) one constant volume, one constant pressure, and two isentropic processes.

52. Carnot cycle has maximum efficiency for

• a) petrol engine
• b) diesel engine
• c) reversible engine
• d) irreversible engine

53. The efficiency of the Carnot cycle may be increased by

• a) increasing the highest temperature.
• b) decreasing the highest temperature.
• c) increasing the lowest temperature.
• d) keeping the lowest temperature constant

54. The efficiency of Carnot cycle depends upon

• a) temperature limits
• b) pressure ratio
• c) volume compression ratio
• d) cut-off ratio and compression ratio

55. It is ……………… to make an engine working on a Carnot cycle.

• a) possible
• b) impossible

56. Stirling cycle consists of

• a) two constant volume and two isentropic processes
• b) two constant pressure and two isothermal processes
• c) two constant volume and two isothermal processes
• d) one constant volume, one constant pressure and two isentropic processes

57. The efficiency of Stirling cycle is ……….. Carnot cycle.

a) greater than b) less than c) equal to

58. The efficiency of Ericsson cycle is ………………. Carnot cycle.

a) greater than b) less than c) equal to

59. Ericsson cycle consists of two constant pressure and two isothermal processes. (True/False)

True

60. Stirling and Ericsson cycles are

• a) reversible cycles
• b) irreversible cycles
• c) semi-reversible cycles
• d) quasi-static cycles

61. The efficiency of Joule cycle is

• a) greater than Carnot cycle
• b) less than Carnot cycle
• c) equal to Carnot cycle
• d) none of these

62. Reversed Joule cycle is known as

• a) Carnot cycle
• b) Bell-Coleman cycle
• c) Rankine cycle
• d) Stirling cycle

63. Otto cycle consists of

• a) two constant volume and two isentropic processes
• b) two constant pressure and two isentropic processes
• c) two constant volume and two isothermal processes
• d) one constant pressure, one constant volume and two isentropic processes

64. Otto cycle is also known as constant volume cycle (True / False )

True

65. Diesel cycle consists of …………… processes.

• a) two constant volume and two isentropic
• b) two constant pressure and two isentropic
• c) two constant volume and two isothermal
• d) one constant pressure, one constant volume and two isentropic

66. The compression ratio is the ratio of total volume to clearance volume (True/False)

True

67. For the same compression ratio, the efficiency of Diesel cycle is ………. Otto cylce.

a) greater than b) less than c) equal to

68. The efficiency of Diesel cycle increases with

• a) decrease in cut-off
• b) increase in cut-off
• c) constant cut-off
• d) none of these

69. The efficiency of Diesel cycle approaches to Otto cycle efficiency when

• a) cut-off increases
• b) cut-off is decreased
• c) cut-off is zero
• d) cut-off is constant

70. The compression ratio for petrol engines is

1. a) 3 to 6
2. b) 5 to 8
3. c) 15 to 20
4. d) 20 to 30

71. The compression ratio for Diesel engine is

1. a) 3 to 6
2. b) 5 to 8
3. c) 15 to 20
4. d) 20 to 30

72. During which of the following process does heat rejection takes place in Carnot cycle?

1. a) Isothermal expansion
2. b) Isentropic expansion
3. c) Isothermal compression
4. d) Isentropic compression

73. The dual combustion cycle consists of one constant pressure, two constant volume and two isentropic processes. (Agree/Disagree)

Agree

74. For the same compression ratio, the efficiency of dual combustion cycle is

1. a) greater than Diesel cycle and less than Otto cycle
2. b) less than Diesel cycle and greater than Otto cycle
3. c) greater than Diesel cycle
4. d) less than Diesel cycle

75. For the same maximum pressure and temperature,

1. a) Otto cycle is more efficient than Diesel cycle (For same comp. ratio)
2. b) Diesel cycle is more efficient than Otto cycle ( For same pressure & temp.)
3. c) Dual cycle is more efficient than Otto and Diesel cycles
4. d) Dual cycle is less efficient than Otto and Diesel cycles

### Thermodynamics Interview Questions for Students

76. The efficiency of Diesel cycle depends upon cut-off ratio and compression ratio (Yes /No)

Yes

77. In closed cycle gas turbine, the air is compresses isentropically (True/False)

True

78. A closed cycle gas turbine works on Joule’s cycle. (True/False)

True

79. A close cycle gas turbine gives …….. efficiency as compared to an open cycle gas turbine.

a) same b) lower c) higher

80. The principal constituents of a fuel are

1. a) carbon and hydrogen
2. b) oxygen and hydrogen
3. c) sulphur and oxygen
4. d) sulphur and hydrogen

81. The amount of heat generated per kg of fuel is known as calorific value (True/False)

True

82. Coke is produced when coal is strongly heated continuously for 42 to 48 hours in the absence of air in a closes vessel (Yes/No) : Yes

83. The hard coke is obtained when cabonisation of coal is carried out at 900 to 1100 .C

84. Steam coal is a non-coking bituminous coal.

85. Petrol is distilled at 65 to 220 .C

86. Kerosene is distilled at 220 to 345 .C

87. Which of the following gas has the highest calorific value?

1. a) coal gas
2. b) producer gas
3. c) Mond gas
4. d) Blast furnace gas

88. The calorific value of gaseous fuel is expressed in kJ/kg. (True)

89. Producer gas is obtained by partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast. (True)

90. The amount of heat given out by the complete combustion of 1 kg of fuel is known as calorific value of solid or liquid fuel. (True/False) : True

91. The bomb calorimeter is used for finding the Higher calorific value of solid and liquid fuels. : True

92. A molecule consisting of one atom is known as monoatomic : True

93. The oxygen atom is ……. times heavier than the hydrogen atom.

a) 2 b) 4 c) 8 d) 16

94. The mass of carbon per kg of fuel gas is given by

11/3 CO2 + 3/7 CO

95. The mass of excess air supplied is equal to 100/23 x Mass of excess oxygen.

96. The atomic mass of nitrogen (14) is less than oxygen (16).

97. The atomic mass of sulphur is

1. 12
2. 14
3. 16
4. 32

98. One molecule of oxygen consists of 2 atoms of oxygen. (True/False) : True

99. Reheating in a gas turbine increase the thermal efficiency : True

100. The condition for a reversible and irreversible cycle