Thermodynamics – Objective Questions

Page 5 : Numerical Concept Builders

Q41. One mole of ideal gas expands isothermally at 300 K from volume V to 2V. Calculate work done.

  • A) 300R ln2
  • B) RT ln2
  • C) 2RT ln2
  • D) Zero

Answer: A

Explanation: W = nRT ln(V₂/V₁) = 1 × R × 300 × ln2

Q42. An ideal gas undergoes an isochoric process. Work done is:

  • A) Positive
  • B) Negative
  • C) Zero
  • D) Maximum

Answer: C

Explanation: Volume constant ⇒ W = ∫PdV = 0

Q43. One mole monoatomic gas is heated at constant volume so that temperature rises by 100 K. Heat supplied is:

  • A) (3/2)R × 100
  • B) (5/2)R × 100
  • C) R × 100
  • D) Zero

Answer: A

Explanation: Q = nCvΔT = (3/2)R × 100

Q44. In adiabatic expansion, the work done comes from:

  • A) External heat
  • B) Internal energy
  • C) Enthalpy
  • D) Kinetic energy of piston

Answer: B

Explanation: No heat exchange ⇒ work done reduces internal energy.

Q45. A gas undergoes a cyclic process. Net change in internal energy is:

  • A) Positive
  • B) Negative
  • C) Zero
  • D) Depends on path

Answer: C

Explanation: Internal energy is a state function.

Q46. During free expansion of an ideal gas:

  • A) Temperature decreases
  • B) Temperature increases
  • C) Temperature remains constant
  • D) Depends on gas

Answer: C

Explanation: No work, no heat ⇒ ΔU = 0 ⇒ T constant.

Q47. A gas expands isobarically. Which is correct?

  • A) Q = W
  • B) Q > W
  • C) Q < W
  • D) Q = 0

Answer: B

Explanation: Heat increases internal energy + work done.

Q48. Which quantity depends only on temperature for ideal gas?

  • A) Pressure
  • B) Volume
  • C) Internal energy
  • D) Work done

Answer: C

Explanation: U = f(T) only.

Q49. For an isothermal process of ideal gas:

  • A) ΔU = 0
  • B) ΔU > 0
  • C) ΔU < 0
  • D) ΔU = W

Answer: A

Explanation: Internal energy depends only on temperature.

Q50. Which process gives maximum work between two fixed volumes?

  • A) Adiabatic
  • B) Isothermal
  • C) Isochoric
  • D) Isobaric

Answer: B

Explanation: Area under isothermal curve is maximum.

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Focus: Numerical clarity + exam-safe logic

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