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Thermodynamics JEE Main MCQ & Practice Questions

Practice Thermodynamics MCQs for JEE Main Chemistry with answers, explanations, chapter revision and related ChemNexa mock tests.

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Thermodynamics Revision Guide for JEE Main Chemistry

Thermodynamics relates heat, work, internal energy, enthalpy and spontaneity. It is best learned through sign conventions and state-function logic rather than isolated memorisation.

For JEE Main Chemistry, revise the first law, enthalpy changes, Hess law, entropy and Gibbs free energy, then practise conceptual and numerical MCQs together.

Important Topics

  • System, surroundings and state functions
  • First law of thermodynamics
  • Enthalpy and heat capacity
  • Hess law
  • Entropy
  • Gibbs free energy and spontaneity

Important Formulae & Relationships

  • ΔU = q + w
  • At constant pressure: qp = ΔH
  • ΔH = ΔU + ΔngRT (for ideal-gas reactions)
  • ΔG = ΔH − TΔS
  • ΔG° = −RT ln K

Use formulas only after checking the required units, sign convention and assumptions for the question.

What to practise in Thermodynamics

Concept Revision

Revise definitions, principles, equations, trends and core ideas from Thermodynamics before attempting MCQs.

Exam-style MCQs

Use chapter-focused multiple-choice practice to improve accuracy, recall and application for JEE Main Chemistry.

Performance Practice

Attempt ChemNexa tests, review results and return to weak areas for another round of targeted revision.

Top 20 Thermodynamics MCQs with Answers

These public questions are selected from the exact Thermodynamics chapter, screened for topic relevance and deduplicated so repeated versions of the same MCQ are not shown publicly. Use them for quick revision, then sign in to attempt the complete test experience with more questions, results and performance review.

JEE Main Chemistry · Thermodynamics · Very Hard

1. The first law of thermodynamics is expressed as:

  • A. ΔU = q + w
  • B. ΔU = q − w in every convention
  • C. ΔU = q/w
  • D. ΔU = 0 always
Answer: A
Explanation: With the chemistry convention, change in internal energy equals heat supplied plus work done on the system.

JEE Main Chemistry · Thermodynamics · Very Hard

2. For a gaseous reaction, the relation is:

  • A. ΔH = ΔU + ΔngRT
  • B. ΔH = ΔU − ΔngRT
  • C. ΔH = ΔU always
  • D. ΔH = qv
Answer: A
Explanation: For ideal gases, the PV contribution gives ΔH = ΔU + ΔngRT.

JEE Main Chemistry · Thermodynamics · Very Hard

3. Gibbs free energy is defined as:

  • A. G = U − PV
  • B. G = q + w
  • C. G = H − TS
  • D. G = H + TS
Answer: C
Explanation: Gibbs energy combines enthalpy and entropy through G = H − TS.

JEE Main Chemistry · Thermodynamics · Very Hard

4. At constant temperature and pressure, a process is spontaneous when:

  • A. ΔH = 0
  • B. ΔG < 0
  • C. ΔG > 0
  • D. ΔG = 0 only
Answer: B
Explanation: A negative Gibbs energy change is the criterion for spontaneity at constant T and P.

JEE Main Chemistry · Thermodynamics · Very Hard

5. The relation between standard Gibbs energy and equilibrium constant is:

  • A. ΔG° = RT ln K
  • B. ΔG° = −K/RT
  • C. ΔG° = RT/K
  • D. ΔG° = −RT ln K
Answer: D
Explanation: Thermodynamics gives ΔG° = −RT ln K.

JEE Main Chemistry · Thermodynamics · Very Hard

6. A process with ΔH < 0 and ΔS > 0 is spontaneous:

  • A. At all temperatures
  • B. Only at high temperature
  • C. Only at low temperature
  • D. At no temperature
Answer: A
Explanation: ΔG = ΔH − TΔS remains negative for all positive temperatures.

JEE Main Chemistry · Thermodynamics · Very Hard

7. Which is a state function?

  • A. Heat
  • B. Work
  • C. Path length
  • D. Internal energy
Answer: D
Explanation: Internal energy depends only on the state, whereas heat and work depend on the path.

JEE Main Chemistry · Thermodynamics · Very Hard

8. For an ideal gas undergoing an isothermal process, ΔU is:

  • A. Equal to pressure
  • B. Zero
  • C. Positive
  • D. Negative
Answer: B
Explanation: Internal energy of an ideal gas depends only on temperature, which remains constant.

JEE Main Chemistry · Thermodynamics · Very Hard

9. For an ideal gas undergoing an isothermal process, ΔH is:

  • A. Zero
  • B. Positive
  • C. Negative
  • D. Equal to q always
Answer: A
Explanation: Enthalpy of an ideal gas depends only on temperature.

JEE Main Chemistry · Thermodynamics · Very Hard

10. At constant pressure, heat exchanged equals:

  • A. −ΔH
  • B. Zero
  • C. ΔH
  • D. ΔU
Answer: C
Explanation: For processes involving only pressure-volume work, qp = ΔH.

JEE Main Chemistry · Thermodynamics · Very Hard

11. The relation between enthalpy and internal energy is:

  • A. H = q + w
  • B. H = U + PV
  • C. H = U − PV
  • D. H = PV/U
Answer: B
Explanation: Enthalpy is defined as H = U + PV.

JEE Main Chemistry · Thermodynamics · Very Hard

12. Hess's law follows from the fact that enthalpy is:

  • A. Equal to entropy
  • B. A state function
  • C. A path function
  • D. Always zero
Answer: B
Explanation: The enthalpy change depends only on initial and final states.

JEE Main Chemistry · Thermodynamics · Very Hard

13. For a spontaneous process in an isolated system, entropy:

  • A. Decreases
  • B. Remains zero
  • C. Becomes negative
  • D. Increases
Answer: D
Explanation: The second law requires ΔSsystem > 0 for spontaneous change in an isolated system.

JEE Main Chemistry · Thermodynamics · Very Hard

14. For a reversible phase transition at equilibrium temperature:

  • A. ΔS = T/ΔH
  • B. ΔS = ΔH×T
  • C. ΔS = 0
  • D. ΔS = ΔH/T
Answer: D
Explanation: For reversible heat transfer, ΔS = qrev/T = ΔHtransition/T.

JEE Main Chemistry · Thermodynamics · Very Hard

15. Which is a path function?

  • A. Entropy
  • B. Internal energy
  • C. Heat
  • D. Enthalpy
Answer: C
Explanation: Heat depends on how a process is carried out.

JEE Main Chemistry · Thermodynamics · Very Hard

16. At constant volume, heat exchanged equals:

  • A. ΔH
  • B. −ΔU
  • C. Zero
  • D. ΔU
Answer: D
Explanation: At constant volume, pressure-volume work is zero, so qv = ΔU.

JEE Main Chemistry · Thermodynamics · Very Hard

17. Heat capacity at constant pressure and constant volume for an ideal gas satisfy:

  • A. Cp + Cv = R
  • B. Cp/Cv = R
  • C. Cp = Cv
  • D. Cp − Cv = R
Answer: D
Explanation: Mayer's relation for one mole of an ideal gas is Cp − Cv = R.

JEE Main Chemistry · Thermodynamics · Very Hard

18. An exothermic reaction has:

  • A. ΔH > 0
  • B. ΔH = 0
  • C. ΔS = 0 necessarily
  • D. ΔH < 0
Answer: D
Explanation: Exothermic reactions release heat, lowering system enthalpy.

JEE Main Chemistry · Thermodynamics · Very Hard

19. An endothermic reaction has:

  • A. ΔH = 0
  • B. ΔG < 0 necessarily
  • C. ΔH > 0
  • D. ΔH < 0
Answer: C
Explanation: Endothermic reactions absorb heat and increase enthalpy.

JEE Main Chemistry · Thermodynamics · Very Hard

20. Standard enthalpy of formation refers to formation of:

  • A. One mole of compound from its elements in standard states
  • B. One gram of compound
  • C. One mole of atoms from ions
  • D. Any amount at any pressure
Answer: A
Explanation: It is defined for one mole of compound formed from constituent elements in standard states.

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Thermodynamics Practice Tests

Thermodynamics Frequently Asked Questions

What causes most Thermodynamics mistakes?

Sign conventions for heat and work, confusing state functions with path functions, and using inconsistent units are common sources of error.

What does negative ΔG indicate?

For a process under the stated conditions, negative Gibbs free-energy change indicates thermodynamic spontaneity.

How should I revise Thermodynamics?

Build a one-page sign-convention and formula sheet, then practise problems that require choosing the correct relation rather than only substituting numbers.

Continue with another chapter to build connected concepts and strengthen your overall Chemistry preparation.

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