Second law of thermodynamics Knowledge-Based Practice

Questions

1. 1.

   According to the second law of thermodynamics, which of the following describes a process that is fundamentally impossible for a cyclic heat engine?

   • A) Discharging waste heat into a low-temperature sink while doing net work on the surroundings
   • B) Absorbing heat from a high-temperature reservoir to perform work with an efficiency less than 100%
   • C) Completely converting heat absorbed from a single thermal reservoir into work without discharging heat to a colder reservoir
   • D) Operating with a thermal efficiency that is strictly less than the Carnot efficiency operating between the same two temperatures
2. 2.

   Based on the second law of thermodynamics, why does heat spontaneously flow only from an object at a higher temperature to an object at a lower temperature?

   • A) The heat transfer causes the hotter object to lose more energy than the colder object gains, thereby lowering the total energy of the universe.
   • B) The transfer of thermal energy completely converts all exchanged heat into mechanical work without any loss to the surroundings.
   • C) The entropy gained by the colder object is greater than the entropy lost by the hotter object, resulting in a net increase in total entropy.
   • D) The heat transfer causes the entropy of both objects to decrease simultaneously until thermal equilibrium is established.
3. 3.

   Liquid water freezes spontaneously at $-10\text{ }^\circ\text{C}$, even though the entropy of the water decreases during this phase change ($\Delta S_{\text{sys}} < 0$). According to the second law of thermodynamics, which statement explains why this process is spontaneous?

   • A) The second law of thermodynamics applies strictly to isolated systems and does not govern closed or open systems.
   • B) The total energy of the universe decreases during freezing, thereby allowing the local entropy of the system to decrease.
   • C) A decrease in system entropy can occur spontaneously only when the surrounding temperature approaches absolute zero.
   • D) The heat released to the surroundings increases the entropy of the surroundings by a magnitude greater than the decrease in system entropy.
4. 4.

   An isolated system is initially held in a non-equilibrium state. According to the second law of thermodynamics, what change occurs in the entropy of the system as it spontaneously evolves toward equilibrium?

   • A) The entropy decreases progressively until it reaches a minimum at equilibrium.
   • B) The entropy remains constant and equal to zero throughout the entire transition.
   • C) The entropy increases progressively until it reaches a maximum at equilibrium.
   • D) The entropy decreases initially and then remains constant at a negative value.
5. 5.

   According to the second law of thermodynamics, which statement correctly describes the condition for any spontaneous process?

   • A) The total enthalpy of the system and its surroundings must decrease.
   • B) The entropy of the system alone must always increase regardless of the surroundings.
   • C) The total entropy of the universe remains constant during an irreversible process.
   • D) The total entropy change of the universe, representing the system plus its surroundings, must be greater than zero.

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