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Systems, surroundings, properties, state functions and processes: NEET MCQs with answers

90 questions on this topic of Chemical Thermodynamics (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. A system is enclosed by rigid, non-conducting (adiabatic) walls. Which of the following boundary interactions can occur between the system and its surroundings?

  1. Exchange of heat only
  2. Neither heat, matter, nor mechanical boundary work can be exchanged
  3. Exchange of matter
  4. Exchange of mechanical work through boundary displacement
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Answer: (B) Neither heat, matter, nor mechanical boundary work can be exchanged

Rigid walls prevent boundary movement, so no expansion or mechanical work (PΔV) can take place. Adiabatic walls prevent any heat exchange (q = 0), and closed/sealed walls prevent the transfer of matter. Therefore, none of these interactions can occur across the boundary.

medium

2. Given below are two statements: Statement I: A quasi-static process is an idealized process carried out infinitesimally slowly such that the system remains practically in thermodynamic equilibrium at all stages. Statement II: All natural (spontaneous) processes occurring in the universe are reversible processes. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
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Answer: (B) Statement I is correct but Statement II is incorrect

Statement I is correct as quasi-static processes proceed with infinitesimal driving forces, keeping the system near equilibrium. Statement II is incorrect because all natural, spontaneous processes occur at finite rates and are inherently irreversible.

hard

3. An ideal gas expands against a constant external pressure from state 1 (P₁, V₁, T₁) to state 2 (P₂, V₂, T₂). For this transformation, which of the following expressions correctly differentiates a state function from a path-dependent quantity?

  1. Both ΔU and w are independent of the path taken
  2. ΔU depends on the path, whereas w depends only on initial and final volumes
  3. Both ΔU and w depend only on the initial and final states
  4. ΔU depends only on (T₂ - T₁), whereas work w depends on P_ext and (V₂ - V₁)
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Answer: (D) ΔU depends only on (T₂ - T₁), whereas work w depends on P_ext and (V₂ - V₁)

For an ideal gas, internal energy is a function of temperature alone, so ΔU = n C_v (T₂ - T₁), which is independent of the path. Work done against a constant external pressure is w = -P_ext (V₂ - V₁), which depends explicitly on the external restraint (path) rather than the internal states alone.

medium

4. Match the thermodynamic processes in Column I with their defining mathematical conditions in Column II: Column I (A) Isochoric process (B) Adiabatic process (C) Isothermal process (D) Isobaric process Column II (1) ΔT = 0 (2) ΔP = 0 (3) q = 0 (4) ΔV = 0

  1. A-4, B-1, C-3, D-2
  2. A-4, B-3, C-1, D-2
  3. A-2, B-3, C-1, D-4
  4. A-3, B-4, C-2, D-1
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Answer: (B) A-4, B-3, C-1, D-2

In an isochoric process, volume remains constant (ΔV = 0). In an adiabatic process, there is no heat exchange (q = 0). In an isothermal process, temperature remains constant (ΔT = 0). In an isobaric process, pressure remains constant (ΔP = 0).

easy

5. Given below are two statements: Statement I: The temperature of a gas is an intensive property, but the total kinetic energy of the gas molecules in a given sample is an extensive property. Statement II: When two identical equilibrium systems each with volume V and temperature T are combined without reaction, the resulting system has volume 2V and temperature 2T. In light of the above statements, choose the correct answer from the options given below:

  1. Both Statement I and Statement II are true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Statement I is false but Statement II is true
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Answer: (C) Statement I is true but Statement II is false

Statement I is true because temperature does not depend on system size (intensive), whereas total kinetic energy equals (3/2)nRT, which depends directly on the quantity of matter (extensive). Statement II is false because temperature is an intensive variable and remains T when two identical equilibrium subsystems at T are combined; only extensive variables like volume double to 2V.

hard

6. Given below are two statements: Statement I: A quasi-static process is an idealized process carried out infinitely slowly such that the system remains in virtual thermodynamic equilibrium with its surroundings at all times. Statement II: All natural or spontaneous processes occurring in the universe are irreversible and proceed at finite rates. In light of the above statements, choose the correct answer:

  1. Both Statement I and Statement II are true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Statement I is false but Statement II is true
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Answer: (A) Both Statement I and Statement II are true

A quasi-static process occurs infinitely slowly through a continuous succession of equilibrium states, which defines an ideal reversible process. Natural or spontaneous processes occur spontaneously at finite rates with non-zero driving forces, making them strictly irreversible.

easy

7. In a rigid, closed container of fixed volume 10 L, an ideal gas is heated from 300 K to 600 K. Which of the following conditions correctly characterizes this process?

  1. w = 0 and ΔV = 0
  2. q = 0 and w ≠ 0
  3. ΔP = 0 and w = 0
  4. ΔT = 0 and q ≠ 0
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Answer: (A) w = 0 and ΔV = 0

A rigid container cannot expand or contract, so ΔV = 0 (isochoric process). Since boundary work is given by ∫ P_ext dV, w = 0.

medium

8. An ideal gas at initial state (P₁, V₁) expands to final volume V₂ via two different paths: Path A is reversible isothermal, and Path B is reversible adiabatic. If the final pressure along Path A is P_iso and along Path B is P_adi, then:

  1. P_iso · P_adi = P₁²
  2. P_iso < P_adi
  3. P_iso = P_adi
  4. P_iso > P_adi
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Answer: (D) P_iso > P_adi

On a P-V diagram, the slope of an adiabatic curve is steeper than that of an isothermal curve by a factor of γ (since (dP/dV)_adi = γ(dP/dV)_iso). Consequently, during expansion to the same final volume V₂, the pressure drops more steeply in the adiabatic process, resulting in P_iso > P_adi.

medium

9. Two moles of an ideal gas are confined in a vessel. Which of the following operations converts an extensive property of the system into an intensive property?

  1. Multiplying total volume by pressure
  2. Adding internal energy to the product of pressure and volume
  3. Dividing total enthalpy by the amount of substance in moles
  4. Multiplying heat capacity by total temperature
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Answer: (C) Dividing total enthalpy by the amount of substance in moles

Dividing an extensive property (such as enthalpy H) by the amount of substance (n) yields a molar quantity (molar enthalpy, H_m = H/n), which is independent of sample size and therefore an intensive property.

medium

10. Consider the following statements regarding state and path functions: Statement I: The change in the value of a state function between two given states is independent of whether the transformation is carried out reversibly or irreversibly. Statement II: Work (w) and heat (q) are state functions because their algebraic sum (q + w) equals the change in internal energy (ΔU). Choose the correct option:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
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Answer: (B) Statement I is correct but Statement II is incorrect

Statement I is correct because state functions depend solely on the initial and final states of the system, not on the path taken. Statement II is incorrect because work and heat are path functions; only their sum (ΔU = q + w), according to the first law of thermodynamics, becomes independent of the path and constitutes a state function.

easy

11. A system exchanges energy with its surroundings exclusively in the form of heat and work, but cannot exchange matter. What type of system is this?

  1. Isolated system
  2. Closed system
  3. Open system
  4. Adiabatic system
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Answer: (B) Closed system

A closed system allows transfer of energy (such as heat and work) across its boundary with the surroundings, but does not allow any transfer of matter. An isolated system allows neither matter nor energy transfer.

hard

12. For a closed system containing a fixed amount of an ideal gas, which of the following operations will keep the value of an extensive property unchanged while changing the value of an intensive property?

  1. Dividing the gas into two equal compartments by an impermeable wall
  2. Heating the gas at constant volume
  3. Doubling the amount of substance at constant temperature and pressure
  4. Isothermal free expansion into vacuum
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Answer: (B) Heating the gas at constant volume

Volume and mass are extensive properties. During heating at constant volume (isochoric process), mass and volume remain constant, while intensive properties like temperature, pressure, and density (or molar internal energy) change.

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