MCQ’s on 2nd and 3rd Law of Thermodynamics and Entropy

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The Second Law of Thermodynamics

The second law of thermodynamics states that any isolated system's entropy always increases. Isolated systems evolve spontaneously towards thermal equilibrium— the system's state of maximum entropy. In simple terms, Universe entropy (the ultimate isolated system) only increases and never decreases.

A straightforward way of thinking about the second law of thermodynamics is that if it is not cleaned and tidy, a room will eventually get messier and messier over time –no matter how careful one is to keep it clean.


The Third Law of Thermodynamics

The third thermodynamic law states that the entropy of a system approaches a constant value as it reaches absolute zero. The entropy of a system at absolute zero usually is zero and is determined in every case only by the number of different ground states it has. Entropy for a pure crystalline material at absolute zero temperature (ideal order) is 0. This statement holds if only one minimum energy condition exists for the perfect crystal.


MCQ’s of 2nd and 3rd Law of Thermodynamics

1. A refrigerator has a performance coefficient of 5. Calculate the ambient heat discharged if the temperature inside the freezer is -20oC

  1. 11oC

  2. 41oC

  3. 21oC

  4. 31oC

Answer: (d)

2. Which of the following factors affects the heat of reaction based on with Kirchhoff Equation

  1. Molecularity

  2. Temperature

  3. Pressure

  4. Volume

Answer: (b)

3. Chemical Dissociation of all reaction is

  1. Exothermic

  2. Reversible

  3. Endothermic

  4. Reversible and Endothermic

Answer: (d)

4. Select the largest unit of Energy

  1. Electron volt

  2. Joule

  3. Calorie

  4. Erg

Answer: (c)

5. What is the unique characteristic feature of a perfect Black Body

  1. A good absorber only

  2. A good radiator

  3. A good absorber and a good radiator

  4. Neither a radiator nor an absorber

Answer: (c)

6. Which Thermodynamic process where heat is not exchanged with the surroundings is

  1. Isothermal

  2. Adiabatic

  3. Isobaric

  4. Isotropic

Answer: (b)


Entropy

In physics and chemistry, entropy is an important concept, and it can be extended to other sciences, including cosmology and economy. It's part of thermodynamics in physics. It is a core concept in physical chemistry.


Importance of MCQ’s 

This series of Multiple-Choice Questions & Answers (MCQs) in Thermodynamics primarily focuses on "Entropy Theory and its Applications."

Solved MCQ’s on Entropy

1. Which of the following is correct?

a) For an isolated system, dS>=0
b) For a reversible process, dS=0
c) For an irreversible process, dS>0
d) All of the mentioned

Answer: d
Explanation: For an isolated system with no exchange of energy with environment Q=0 and also dS>=dQ / T.

2. According to the entropy theorem, entropy of an isolated system can never decrease and will remain constant only when the process is reversible.

a) True
b) False

Answer: a
Explanation: This is the declaration for the principle of increase of entropy.

3. Entropy may decline locally in somewhere within the isolated system. How can one clarify this statement?

a) This cannot be possible
b) This is possible because it can decrease the entropy of an isolated system.
c) This must be balanced by increased entropy somewhere within the system.
d) None of the mentioned

Answer: c
Explanation: The net effect of an irreversible process is an increase in entropy of the entire system.

4.Clausius summed up the first and second laws concerning thermodynamics as

a) The energy of the world is constant
b) The entropy tends towards a maximum
c) Both of the mentioned
d) None of the mentioned

Answer: c
Explanation: Clausius gave these two statements.

5. The entropy of an isolated system continuously ____ and becomes a ____ at the state of equilibrium.
a) decreases, minimum
b) increases, maximum
c) increases, minimum
d) decreases, maximum

Answer: b
Explanation: If an isolated system’s entropy differs with some parameter, then that parameter has a certain value that maximizes the entropy.

6. The entropy principle is the quantitative statement of the second law of thermodynamics.
a) True
b) False

Answer: a
Explanation: This is an over-all fact about the entropy principle.

7. Which of the following may be regarded as applying the principle of entropy?
a) Transfer of heat through a finite temperature difference
b) Mixing of two fluids
c) Maximum temperature attainable from two finite bodies
d) All of the mentioned

Answer: d
Explanation: These are some general applications of entropy principle.

8. The final temperatures of two bodies, initially at T1 and T2 can range from
a) (T1-T2)/2 to (T1*T2)  
b) (T1+T2)/2 to (T1*T2)  
c) (T1+T2)/2 to (T1*T2)
d) (T1-T2)/2 to (T1*T2)

Answer: b
Explanation: (T1+T2)/2 is when no work is done, and sqrt(T1*T2) is the temperature with maximum work distribution.

9.Which of the following processes exhibit external mechanical Irreversibility?

a) Isothermal dissipation of work
b) Adiabatic dissipation of work
c) Both of the mentioned
d) None of the mentioned

Answer: c
Explanation: These processes reveal external mechanical irreversibility.

10. Which of the following laws was expressed by Nernst?

a) The first law of thermodynamics

b) The second law of thermodynamics

c) Third law of thermodynamics

d) None of the above

Answer: (c)