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NEET Physics: The second law of thermodynamics Practice Questions

15 free multiple-choice questions on The second law of thermodynamics (Thermodynamics) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. For a process to be reversible, the change in entropy of the universe must be:

    • Ainfinite
    • Bpositive
    • Czero
    • Dnegative
    Show answer & explanation

    Correct answer: C — zero

    A reversible process occurs when the change in entropy of the universe is exactly zero (as per the condition for reversibility in the context of the Second Law).

  2. Q2. Which of the following statements is the fundamental statement of the Second Law of Thermodynamics?

    • AThe total entropy of an isolated system is either constant or increases.
    • BWork done is always converted entirely into heat in a reversible process.
    • CHeat flows spontaneously from a colder body to a hotter body.
    • DThe total entropy of an isolated system always decreases.
    Show answer & explanation

    Correct answer: A — The total entropy of an isolated system is either constant or increases.

    The Second Law states that for any spontaneous process, the total entropy of the universe (or an isolated system) must increase. If the process is reversible, the entropy remains constant.

  3. Q3. If a process is irreversible, it means that the total entropy change of the universe is:

    • Anegative
    • Bzero
    • Cpositive
    • Dundefined
    Show answer & explanation

    Correct answer: C — positive

    Irreversible processes always result in an increase in the total entropy of the universe, as the process generates some entropy.

  4. Q4. Which of the following processes is generally considered irreversible based on the Second Law of Thermodynamics?

    • AFree expansion of a gas into a vacuum.
    • BAdiabatic compression.
    • CReversible isothermal expansion.
    • DIsothermal compression in a closed system.
    Show answer & explanation

    Correct answer: A — Free expansion of a gas into a vacuum.

    Free expansion into a vacuum is an irreversible process because the system naturally moves to a state of higher entropy.

  5. Q5. For an isolated system, the change in entropy is governed by which principle of the Second Law of Thermodynamics?

    • AConservation of Energy
    • BFirst Law of Thermodynamics
    • CThe property of increasing entropy
    • DClausius Inequality
    Show answer & explanation

    Correct answer: C — The property of increasing entropy

    For an isolated system, the entropy always tends to increase, which is the fundamental statement of the Second Law when applied to isolated systems.

  6. Q6. Which quantity is used to measure the dispersal of energy in a system?

    • AEnthalpy
    • BWork
    • CInternal Energy
    • DEntropy
    Show answer & explanation

    Correct answer: D — Entropy

    Entropy (S) is the thermodynamic property that quantifies the degree of disorder or the dispersal of energy within a system.

  7. Q7. Which of the following statements is a direct consequence of the Second Law of Thermodynamics regarding spontaneous processes in the universe?

    • AThe entropy of an isolated system always decreases.
    • BThe entropy of an isolated system always increases.
    • CHeat naturally flows from a colder body to a hotter body.
    • DThe total energy of an isolated system remains constant.
    Show answer & explanation

    Correct answer: B — The entropy of an isolated system always increases.

    The Second Law of Thermodynamics states that for any spontaneous process in an isolated system, the total entropy of the system (and its surroundings) will increase.

  8. Q8. The change in entropy (ΔS) for an irreversible process occurring in an isolated system is:

    • ADepends on the initial temperature
    • BAlways zero
    • CAlways positive
    • DAlways negative
    Show answer & explanation

    Correct answer: C — Always positive

    According to the Second Law, for an irreversible process in an isolated system, the entropy of the system must increase (ΔS > 0).

  9. Q9. Which of the following statements correctly describes the Second Law of Thermodynamics in terms of entropy?

    • AThe total energy of an isolated system is constant.
    • BThe entropy of an isolated system always decreases.
    • CHeat spontaneously flows from a cold body to a hot body.
    • DThe entropy of an isolated system always increases.
    Show answer & explanation

    Correct answer: D — The entropy of an isolated system always increases.

    The Second Law states that for any spontaneous process in an isolated system, the total entropy of the system increases.

  10. Q10. In the context of the Second Law, an irreversible process necessarily implies:

    • AThe process occurs at zero temperature.
    • BThere is no net increase in energy.
    • CThere is a net increase in the total entropy of the universe.
    • DThe process is perfectly reversible.
    Show answer & explanation

    Correct answer: C — There is a net increase in the total entropy of the universe.

    Irreversible processes generate entropy, meaning the total entropy of the universe increases, which is a direct consequence of the Second Law.

  11. Q11. The process of heat flowing spontaneously from a hot body to a cold body is an example of a process that is:

    • AIsothermal
    • BIrreversible
    • CAdiabatic
    • DReversible
    Show answer & explanation

    Correct answer: B — Irreversible

    Heat spontaneously flows from hot to cold, but the reverse process (cold to hot) requires external work and is irreversible.

  12. Q12. The concept of entropy is fundamentally related to which property of a thermodynamic system?

    • AInternal Energy
    • BDisorder or randomness
    • CWork done
    • DTemperature
    Show answer & explanation

    Correct answer: B — Disorder or randomness

    Entropy is a measure of the randomness or the number of microscopic arrangements (microstates) available to the system, which is directly related to thermodynamic disorder.

  13. Q13. Entropy (S) is a measure of:

    • AThe potential energy of a system.
    • BThe disorder or randomness of a system.
    • CInternal energy of a system.
    • DThe rate of heat transfer.
    Show answer & explanation

    Correct answer: B — The disorder or randomness of a system.

    Entropy is a measure of the dispersal of energy or the number of microscopic configurations a system can occupy, which is directly related to its disorder.

  14. Q14. The process of warming up a gas in a container is an example of a process that is:

    • AAdiabatic.
    • BIsothermal.
    • CIsobaric.
    • DSpontaneous.
    Show answer & explanation

    Correct answer: D — Spontaneous.

    Warming up a gas typically involves heat transfer, and if the surroundings are at a higher temperature, the process is spontaneous and results in an increase in entropy.

  15. Q15. The Clausius statement of the Second Law primarily relates to the direction of heat flow between two bodies. It states that heat cannot spontaneously flow from a colder body to a hotter body. This implies that the process is:

    • AReversible.
    • BCyclical.
    • CStatic.
    • DIrreversible.
    Show answer & explanation

    Correct answer: D — Irreversible.

    The statement establishes a directionality for heat transfer, implying that heat naturally flows from high temperature to low temperature, which is an irreversible flow tendency.

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