ArulmiguMeenakshi Amman College of Engineering
Vadamavandal-604410.
Impotant questions and answers
ENGINEERING THERMODYNAMICS
Prepared by
V.Umapathy,
Prof. /Mech.
S.No. Questions and answers
Unit-I
BASICS, ZEROTH AND FIRST LAW
2 – marks question and answers
1. Define thermodynamics?
Thermodynamics is a branch of science which deals relations between heat, work and properties of the
system.
2. Define work.
The product of pressure and change of volume is called work. It is generally denoted as w and its unit is kJ.
W = ∫ 𝑃𝑑𝑣.
3. Define intensive property with an example.
The property independent of mass is called intensive property. Example: Pressure, Temperature, Specific
volume etc.
4. Define isolated system.
No mass transfer or heat transfer or work transfer take place that type of system is called isolated system.
This is imaginary system. Example: Entire universe.
,5. Define internal energy.
The heat energy stored in the gas at a given temperature is called internal energy. It is generally denoted as
U.U = m Cv (T2-T1) kJ.m= Mass of the substance, Cv= Specific heat at constant volume, T 2=Maximum
temperature and T1= Minimum temperature.
6. Define enthalpy.
The combination of flow energy and internal energy is called enthalpy. It is generally denoted as h. h=
u+pv kJ. U=internal energy, p= pressure, v= volume.
7. What is thermodynamic equilibrium?
There is no change in temperature, no chemical reactions and no mechanical movements this type of
equilibrium is called thermodynamic equilibrium.
8. Explain state of a system.
It is the condition of the system at any particular moment.
The state is identified by a statement of properties such as pressure, volume, temperature, etc. of the
system. To specify the state of a system at least two properties are required. A system undergoes a change
from the state 1 to the other 2 due to heat or work transfer. PV diagram shown in figure.
9. State first Law of thermodynamics?
Any cyclic process total heat transfer equal to total work done.
It also states that heat and woke are mutually convertible.
10. What is the zeroth law of thermodynamics?
The zeroth law of thermodynamics states that if two bodies are each in thermal equilibrium with some
third body, then they are also in equilibrium with each other.
13 and 15 marks question and answers
11. 3 Ο
0.35 m of air at 22 C and under atmospheric pressure is heated under constant volume to a
temperature of 100Ο C. Determine: mass of air, the final pressure, heat transfer, the change in
internal energy, the work done , the change in enthalpy and the change of entropy. Assume C p = 1
KJ/kg K and Cv = 0.71 KJ/Kg K.
,
, 12. 2.5 Kg of an ideal gas expanded from a pressure of 7 bars and volume of 1.5 m3 to a pressure of 1.4
bars and volume 4.5 m3. The change in internal energy is 500 KJ. Specific heat at constant volume is
0.72 KJ/KgK. Determine: gas constant, indexof polytrophic expansion, works done, initial
temperature and final temperature.
Vadamavandal-604410.
Impotant questions and answers
ENGINEERING THERMODYNAMICS
Prepared by
V.Umapathy,
Prof. /Mech.
S.No. Questions and answers
Unit-I
BASICS, ZEROTH AND FIRST LAW
2 – marks question and answers
1. Define thermodynamics?
Thermodynamics is a branch of science which deals relations between heat, work and properties of the
system.
2. Define work.
The product of pressure and change of volume is called work. It is generally denoted as w and its unit is kJ.
W = ∫ 𝑃𝑑𝑣.
3. Define intensive property with an example.
The property independent of mass is called intensive property. Example: Pressure, Temperature, Specific
volume etc.
4. Define isolated system.
No mass transfer or heat transfer or work transfer take place that type of system is called isolated system.
This is imaginary system. Example: Entire universe.
,5. Define internal energy.
The heat energy stored in the gas at a given temperature is called internal energy. It is generally denoted as
U.U = m Cv (T2-T1) kJ.m= Mass of the substance, Cv= Specific heat at constant volume, T 2=Maximum
temperature and T1= Minimum temperature.
6. Define enthalpy.
The combination of flow energy and internal energy is called enthalpy. It is generally denoted as h. h=
u+pv kJ. U=internal energy, p= pressure, v= volume.
7. What is thermodynamic equilibrium?
There is no change in temperature, no chemical reactions and no mechanical movements this type of
equilibrium is called thermodynamic equilibrium.
8. Explain state of a system.
It is the condition of the system at any particular moment.
The state is identified by a statement of properties such as pressure, volume, temperature, etc. of the
system. To specify the state of a system at least two properties are required. A system undergoes a change
from the state 1 to the other 2 due to heat or work transfer. PV diagram shown in figure.
9. State first Law of thermodynamics?
Any cyclic process total heat transfer equal to total work done.
It also states that heat and woke are mutually convertible.
10. What is the zeroth law of thermodynamics?
The zeroth law of thermodynamics states that if two bodies are each in thermal equilibrium with some
third body, then they are also in equilibrium with each other.
13 and 15 marks question and answers
11. 3 Ο
0.35 m of air at 22 C and under atmospheric pressure is heated under constant volume to a
temperature of 100Ο C. Determine: mass of air, the final pressure, heat transfer, the change in
internal energy, the work done , the change in enthalpy and the change of entropy. Assume C p = 1
KJ/kg K and Cv = 0.71 KJ/Kg K.
,
, 12. 2.5 Kg of an ideal gas expanded from a pressure of 7 bars and volume of 1.5 m3 to a pressure of 1.4
bars and volume 4.5 m3. The change in internal energy is 500 KJ. Specific heat at constant volume is
0.72 KJ/KgK. Determine: gas constant, indexof polytrophic expansion, works done, initial
temperature and final temperature.
