Second law of thermodynamics and reversibility - Question Bank

1. The Carnot efficiency is the maximum theoretical efficiency for a heat engine operating between two temperatures. This maximum efficiency is achieved by a:
A) Real engine with no friction
B) Real engine with perfect insulation
C) Hypothetical reversible engine
D) Engine operating at constant pressure
2. Which of the following implies that it is impossible to achieve 100% efficiency in converting heat into work in a cyclic process?
A) First Law of Thermodynamics
B) Second Law of Thermodynamics
C) Third Law of Thermodynamics
D) Law of Conservation of Mass
3. Friction in a mechanical system leads to an increase in:
A) Available energy
B) Entropy
C) System stability
D) Potential energy
4. The total entropy of an isolated system can never decrease. This is a statement of:
A) The First Law of Thermodynamics
B) The Second Law of Thermodynamics
C) The Third Law of Thermodynamics
D) The Zeroth Law of Thermodynamics
5. A process that can be reversed by an infinitesimal change in conditions is called:
A) Spontaneous
B) Irreversible
C) Reversible
D) Adiabatic
6. The statement 'Heat cannot spontaneously flow from a colder body to a hotter body' is equivalent to which law?
A) Zeroth Law of Thermodynamics
B) First Law of Thermodynamics
C) Second Law of Thermodynamics
D) Third Law of Thermodynamics
7. If a process is reversible, then the change in entropy of the universe is:
A) > 0
B) < 0
C) = 0
D) Cannot be determined
8. Which of the following is an example of a process that increases the entropy of the universe?
A) A reversible adiabatic expansion.
B) A reversible isothermal compression.
C) The free expansion of a gas into a vacuum.
D) A reversible phase change at constant temperature and pressure.
9. The Second Law of Thermodynamics is fundamentally about the directionality of processes and the concept of:
A) Energy conservation
B) Momentum transfer
C) Entropy increase
D) Charge neutrality
10. Which of the following is a necessary condition for a process to be reversible?
A) It must be adiabatic.
B) It must be isothermal.
C) The driving force must be infinitesimally larger than the opposing force.
D) It must occur rapidly.
11. The change in entropy of a system during an irreversible process is:
A) Always greater than the heat added divided by temperature.
B) Always less than the heat added divided by temperature.
C) Equal to the heat added divided by temperature.
D) Zero
12. For a heat engine, the coefficient of performance (COP) is defined as:
A) Work output / Heat input
B) Heat output / Work input
C) Work input / Heat output
D) Heat input / Work output
13. The process of mixing two different gases at the same temperature and pressure is:
A) Reversible
B) Irreversible
C) Adiabatic
D) Isothermal
14. Carnot's theorem states that no engine operating between two heat reservoirs can be more efficient than a:
A) Real engine
B) Stirling engine
C) Carnot engine
D) Otto engine
15. If a process occurs such that the entropy of the system decreases, but the entropy of the surroundings increases by a larger amount, the process is:
A) Reversible
B) Irreversible and spontaneous
C) Irreversible and non-spontaneous
D) In equilibrium
16. Which statement best describes the relationship between entropy and irreversibility?
A) Irreversible processes decrease entropy.
B) Reversible processes increase entropy.
C) Irreversible processes always increase the total entropy of the universe.
D) Entropy is a measure of the reversibility of a process.
17. The second law of thermodynamics places a fundamental limit on:
A) The total amount of energy in the universe.
B) The efficiency of converting heat into work.
C) The speed of chemical reactions.
D) The possibility of reaching absolute zero temperature.
18. Which of the following conditions is necessary for a process to be reversible?
A) The system must be isolated.
B) The process must involve no heat transfer.
C) The system must be in equilibrium with its surroundings at all times.
D) The process must be spontaneous.
19. The total entropy change for a reversible process involving a system and its surroundings is:
A) Always positive
B) Always negative
C) Always zero
D) Can be positive or negative
20. A system is in thermodynamic equilibrium if:
A) It is undergoing a rapid process.
B) Mechanical, thermal, and chemical equilibrium exist simultaneously.
C) Its entropy is at a minimum.
D) It is exchanging heat with its surroundings.
21. Which of the following phenomena is a direct manifestation of the Second Law of Thermodynamics?
A) The expansion of gases upon heating.
B) The rusting of iron.
C) The flow of heat from a hotter body to a colder body.
D) The change of state from solid to liquid.
22. In a reversible adiabatic process, the change in entropy is:
A) Positive
B) Negative
C) Zero
D) Indeterminate
23. The mathematical expression for the Clausius inequality for any process is:
A) ∮ dQ/T ≤ 0
B) ∮ dQ/T ≥ 0
C) ∮ dQ/T = 0
D) ∮ dQ/T < 0
24. A refrigerator is a device that moves heat from a colder region to a hotter region. According to the Second Law, this process requires:
A) A decrease in entropy of the surroundings.
B) An increase in the entropy of the system.
C) External work input.
D) No energy input.
25. Which statement is true for a cyclic process?
A) The change in internal energy is always zero.
B) The change in entropy is always zero.
C) The change in enthalpy is always zero.
D) The net heat absorbed equals the net work done.
26. The efficiency of a real heat engine is always less than that of a Carnot engine operating between the same temperatures because:
A) The Carnot engine is a theoretical ideal.
B) Real processes are irreversible.
C) The hot reservoir temperature is too high.
D) The cold reservoir temperature is too low.
27. Which statement is incorrect regarding reversible processes?
A) They are idealizations.
B) They occur infinitely slowly.
C) They produce no net change in the surroundings.
D) They always increase the total entropy.
28. For a spontaneous process in an isolated system, the change in entropy (ΔS) must be:
A) ΔS < 0
B) ΔS = 0
C) ΔS > 0
D) ΔS ≥ 0
29. Which of the following is a measure of the unavailability of energy to do work?
A) Enthalpy
B) Entropy
C) Internal Energy
D) Gibbs Free Energy
30. The term 'entropy' was introduced by:
A) James Joule
B) Lord Kelvin
C) Rudolf Clausius
D) Sadi Carnot
31. The second law of thermodynamics implies that:
A) Heat can be converted entirely into work.
B) Work can be converted entirely into heat.
C) It is impossible to transfer heat from a cold body to a hot body without external work.
D) The temperature of a system can never reach absolute zero.
32. Which of the following is a condition for a process to be reversible?
A) The process involves friction.
B) The process is carried out very rapidly.
C) The process is carried out infinitesimally slowly, maintaining equilibrium.
D) The system is insulated.
33. A heat engine operates between 500 K and 300 K. Its maximum possible efficiency is:
A) 20%
B) 40%
C) 60%
D) 80%
34. The maximum possible efficiency of a heat engine operating between two temperatures T_H (hot reservoir) and T_C (cold reservoir) is given by:
A) 1 - (T_C / T_H)
B) 1 - (T_H / T_C)
C) (T_H - T_C) / T_H
D) (T_H - T_C) / T_C
35. Which statement about reversible processes is correct?
A) They are always spontaneous.
B) They are always infinitely fast.
C) They can be reversed by an infinitesimal change in conditions, restoring both system and surroundings to their original states.
D) They always result in a decrease in entropy.
36. In any irreversible process, the entropy of the universe:
A) Decreases
B) Remains constant
C) Increases
D) Can fluctuate
37. For a reversible process, the change in entropy is given by:
A) dS = dQ/T
B) dS = -dQ/T
C) dS = dW/T
D) dS = dQ*T
38. Which of the following processes is irreversible?
A) Isothermal expansion of an ideal gas into vacuum.
B) Melting of ice at 0°C.
C) Free expansion of a gas.
D) Condensation of steam at 100°C.
39. The Kelvin-Planck statement of the Second Law of Thermodynamics states that:
A) It is impossible to construct a device which operates in a cycle and produces no effect other than the transfer of heat from a colder body to a hotter body.
B) It is impossible to construct a device which operates in a cycle and produces no effect other than the extraction of heat from a single reservoir and the performance of an equivalent amount of work.
C) The entropy of a system is always positive.
D) Heat cannot spontaneously flow from a hotter object to a colder object.
40. The Clausius statement of the Second Law of Thermodynamics states that:
A) It is impossible to construct a device which operates in a cycle and produces no effect other than the extraction of heat from a single reservoir and the performance of an equivalent amount of work.
B) It is impossible to construct a device which operates in a cycle and produces no effect other than the transfer of heat from a colder body to a hotter body.
C) The entropy of the universe is constantly increasing.
D) The efficiency of a heat engine is always less than unity.
41. Which of the following is NOT a statement of the Second Law of Thermodynamics?
A) Kelvin-Planck statement
B) Clausius statement
C) Joule's law
D) Carnot's theorem
42. The Carnot cycle is an example of a:
A) Reversible cycle
B) Irreversible cycle
C) Adiabatic cycle
D) Isothermal cycle
43. Which statement is true for any irreversible process?
A) The total entropy change of the system and surroundings is zero.
B) The total entropy change of the system and surroundings is negative.
C) The total entropy change of the system and surroundings is positive.
D) The system's entropy decreases.
44. According to the Second Law of Thermodynamics, the entropy of an isolated system:
A) Always decreases
B) Remains constant
C) Always increases or remains constant
D) Can increase or decrease unpredictably
45. The concept of entropy is most closely associated with:
A) The conservation of energy
B) The amount of heat transferred
C) The degree of disorder or randomness in a system
D) The work done by a system
46. Which of the following conditions must be met for a process to be considered reversible?
A) The system must be isolated.
B) The process must occur infinitely slowly, with the system always in equilibrium.
C) The surrounding temperature must remain constant.
D) There must be no change in the state of the universe.
47. A process is said to be reversible if:
A) It occurs rapidly.
B) It can be reversed by an infinitesimal change in a condition.
C) It generates a lot of heat.
D) It leads to an increase in entropy.
48. Which of the following is a direct consequence of the Second Law of Thermodynamics?
A) Conservation of energy
B) The universe tends towards maximum entropy
C) The existence of absolute zero
D) The impossibility of perpetual motion machines of the first kind
49. Which of the following statements best describes the Second Law of Thermodynamics?
A) Energy can neither be created nor destroyed.
B) In any real process, the total entropy of an isolated system will always increase over time.
C) The absolute zero temperature is unattainable.
D) The efficiency of a heat engine is always 100%.
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