Thermodynamics MCQ Set 7

Q1. The internal energy of an ideal gas is independent of:

A) Temperature
B) Pressure
C) Volume
D) Mass

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Answer: C) Volume
Explanation: For an ideal gas, internal energy depends only on temperature.

Q2. Heat cannot flow from cold to hot body without external work — this statement is given by:

A) Kelvin-Planck
B) Clausius
C) Joule
D) Boyle

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Answer: B) Clausius
Explanation: Clausius statement of the second law describes the natural direction of heat flow.

Q3. The unit of the gas constant R is:

A) kJ/kg·K
B) J/kg·K
C) kJ/mol·K
D) J/mol·K

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Answer: B) J/kg·K
Explanation: In thermodynamics, R = 287 J/kg·K for air (specific gas constant).

Q4. The temperature at which a pure substance changes phase is called:

A) Boiling point
B) Melting point
C) Saturation temperature
D) Critical temperature

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Answer: C) Saturation temperature
Explanation: It’s the temperature where phase change occurs at a given pressure.

Q5. The work done during an isothermal expansion of an ideal gas is given by:

A) W = nRT ln(V₂/V₁)
B) W = PΔV
C) W = mCₚΔT
D) W = 0

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Answer: A) W = nRT ln(V₂/V₁)
Explanation: Derived from the first law of thermodynamics for isothermal processes.

Q6. The property that measures the ability of a substance to transfer heat is:

A) Density
B) Conductivity
C) Entropy
D) Specific heat

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Answer: B) Conductivity
Explanation: Thermal conductivity defines how easily heat passes through a material.

Q7. The lowest temperature possible is known as:

A) Freezing point
B) Triple point
C) Absolute zero
D) Zero Celsius

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Answer: C) Absolute zero
Explanation: At 0 K, all molecular motion theoretically stops.

Q8. A system is said to be in thermodynamic equilibrium when:

A) Temperature is constant
B) Pressure is constant
C) Chemical composition is constant
D) All of the above

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Answer: D) All of the above
Explanation: Thermal, mechanical, and chemical equilibrium must exist simultaneously.

Q9. The process in which both pressure and temperature change but volume remains constant is:

A) Isochoric
B) Isobaric
C) Isothermal
D) Polytropic

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Answer: A) Isochoric
Explanation: Volume is constant while other properties may vary.

Q10. The work input to a heat pump is used to:

A) Absorb heat from the cold body
B) Reject heat to the cold body
C) Increase the internal energy
D) Reduce entropy

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Answer: A) Absorb heat from the cold body
Explanation: A heat pump uses work to extract heat from a cold region and deliver it to a hot region.