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Thermodynamics Viva Questions

Module 1

1. What is meant by thermodynamic system? How do you classify it?

Ans:

Thermodynamic system is defined as the any space or matter or group of matter where the energy transfer or energy conversions are studied. It may be classified into three types
   (a) Open system When a system has both mass and energy transfer it is called as open system.
   Example: Air Compressor.
   (b) Closed system When a system has only heat and work transfer, but there is no mass transfer, it is called as closed system.
   (c) Isolated system Isolated system is not affected by surroundings. There is no heat, work and mass transfer take place. In this system total energy remains constant.
   (d) Adiabatic system A system in which there is no transfer of heat between the system and surrounding is called an adiabatic system.

2. What is meant by surroundings? What is boundary?

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Any other matter out side the system boundary is called as surroundings. System and surroundings are separated by an imaginary line is called boundary.

3. How do you classify the property?

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Thermodynamic property can be classified into two types
I. Intensive or Intrinsic The properties which are independent on the mass of the system is called intensive properties. e.g., Pressure, Temperature, Specific Volume etc.,
II. Extensive and Extrinsic property The properties which are dependent on the mass of the system is called extensive properties. e.g., Total energy, Total volume, weight etc.

4.State the First law of thermodynamics

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First of thermodynamics states that when system undergoes a cyclic process the net heat transfer is equal to work transfer

5. Define: PMM of first kind (perpetual motion machine)

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PMM of first kind delivers work continuously without any input. It violates first law of thermodynamics, It is impossible to construct an engine working with this principle.

6. What is meant by thermodynamic equilibrium

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I. When a system is in thermodynamic equilibrium, it should satisfy the following three conditions. Mechanical Equilibrium :- Pressure remains constant
II. Thermal equilibrium :- Temperature remains constant
III. Chemical equilibrium: There is no chemical reaction.

7. What is Quasi – Static process?

Ans:

The process is said to be quasi – static, it should proceed infinitesimally slow and follows continuous series of equilibrium states. Therefore, the quasi static, it should proceed infinitesimally slowly and follows continuous series of equilibrium states. Therefore, the quasi static process may be a reversible process.

8. What is meant by Point and Path function?

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The quantities which is independent on the process or path followed by the system is known as point functions. Example: Pressure, volume, temperature, etc.,
The quantities which are dependent on the process or path followed by the system is known as path functions. Example: Heat transfer, work transfer.

9. Explain Zeroth Law of thermodynamics?

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Zeroth law of thermodynamics states that when two systems are separately in thermal equilibrium with a third system, then they themselves are in thermal equilibrium with each other

10. Define the term enthalpy, internal energy, Heat, entropy of a pure substance

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Enthalpy The Combination of internal energy and flow energy is known as enthalpy of the system. It may also be defined as the total heat of the substance.
Internal energy Internal energy of a gas is the energy stored in a gas due to its molecular interactions.
Heat Heat is the energy crossing the boundary due to the temperature difference between the system and surroundings.
Entropy of a pure substance Entropy is an important thermodynamic property, which increases with addition of heat and decreases with its removal. Entropy is a function of temperature only. It is an unavailability of energy during energy transfer

11. Define an isentropic process.

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Isentropic process is also called as reversible adiabatic process. It is a process which follows the law of pVy = C is known as isentropic process. During this process entropy remains constant and no heat enters or leaves the gas

12. Explain the throttling process.

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When a gas or vapor expands and flows through an aperture of small size, the process is called as throttling process.

13. What is meant by steady flow process?

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During the process the rate of flow of mass and energy across the boundary remains constant, is known as steady flow process.

14. What is the difference between steady flow and non – flow process?

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During the steady flow process the rate of flow of mass and energy across the boundary remains constant. In case of non – flow across the system and boundary.

15. Give statements of boyle law, Charles law, Gay Lussac law, Avogadro's law.

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boyle law This law was formulated by Robert Boyle. Boyle's law states that the absolute pressure of a given mass of an ideal gas is inversely proportional to its volume, if the temperature of the gas is kept constant.
Charles law This law was formulated by Jacques A.C. Charles. It states that the volume of a given mass of an ideal gas is directly proportional to its absolute temperature if the pressure of the gas is kept constant.
Gay Lussac law This law was formulated by Gay Lussac. The absolute pressure of a given mass of an ideal gas is proportional to temperature if the volume of gas is kept constant.
Avogadro's law Avogadro's law states that equal volume of different ideal gases at the same pressure and temperature contain the same number of molecules.

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