🛠️ JEE🧲 Physics

Thermodynamics

3 solved JEE Physics previous year questions on Thermodynamics, each with the correct answer and a full explanation.

500 J of energy is transferred as heat to 0.5 mol of Argon gas at 298 K and 1.00 atm . The final temperature and the change in internal energy respectively are (Given : ) [JEE Main 2025, 29 Jan (Shift 1)]

a378 K and 300 J

b348 K and 300 J

c368 K and 500 J

d378 K and 500 J

✓ Correct answer: b) 348 K and 300 J

ExplanationArgon is a monoatomic ideal gas At constant pressure: Q = nCₚΔT For monoatomic gas: Cₚ = (5/2)R Q = n × (5/2)R × ΔT 500 = 0.5 × (5/2) × 8.3 × ΔT (5/2) × 8.3 = 20.75 500 = 0.5 × 20.75 × ΔT 500 = 10.375 × ΔT ΔT = 500 / 10.375 ≈ 48 K T₂ = 298 + 48 = 346 K ≈ 348 K For monoatomic gas: ΔU = n × (3/2)R × ΔT = 0.5 × (3/2 × 8.3) × 48 = 0.5 × 12.45 × 48 ≈ 300 J Final Answer: 348 K and 300 J

Which of the following statements is false?

aGibbs free energy is path function.

bTemperature is a state function.

cChange in the state is completely defined when the initial and final states are specified.

dWork appears at the boundary of the system.

✓ Correct answer: a) Gibbs free energy is path function.

ExplanationFalse Statement: (A) Gibbs free energy is a state function.Reason: It does not depend on the path taken between two states.

Which of the following is not correct?

aG is positive for a non-spontaneous reaction

bG is positive for a spontaneous reaction

cG is negative for a spontaneous reaction

dG is zero for a reversible reaction

✓ Correct answer: b) G is positive for a spontaneous reaction

Explanation“ΔG is positive for a spontaneous reaction” is incorrect.For spontaneity ΔG < 0; a positive ΔG indicates non-spontaneity.

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