83 free MCQs on Thermodynamics, each with its own worked answer and explanation. Laws of thermodynamics, heat engines, entropy, and gas processes.
Take the timed Thermodynamics chapterwise test →83 practice questions on Thermodynamics, sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Thermodynamics notes.
The Carnot cycle alternates two isothermal steps (heat absorbed at TH, released at TC) with two adiabatic steps (no heat exchange); the enclosed loop area equals the net work output, and η = 1−TC/TH is the maximum possible efficiency between those two temperatures.
Q1.
A thermodynamic process carried out at constant pressure is called:
Q2.
On a P-V diagram, the area under the curve represents:
Q3.
No engine can be more efficient than a Carnot engine between the same two temperatures. This follows from:
Q4.
A quasi-static process is best described as one that is:
Q6.
Conversion formula from Celsius to Kelvin is:
Q7.
The first law of thermodynamics is basically:
Q8.
During an isothermal process:
Q9.
In an adiabatic process:
Q10.
Ideal gas equation is:
Q11.
Zeroth law of thermodynamics defines:
Q12.
A Carnot engine operates between temperatures 300 K and 600 K. Its efficiency is:
Q13.
The second law of thermodynamics states that entropy of an isolated system:
Q14.
Boyle's law states that at constant temperature:
Q15.
Q = mcT formula is used to calculate:
Q16.
Specific heat of water is approximately:
Q17.
A refrigerator works on which principle?
Q18.
Internal energy of an ideal gas depends only on:
Q19.
Charles law states that at constant pressure:
Q20.
Latent heat is the heat exchanged during:
Q21.
Thermal efficiency of a heat engine is defined as:
Q22.
In an isochoric (constant volume) process, work done by the gas is:
Q23.
Avogadro's number is:
Q24.
Heat flows spontaneously from:
Q25.
In one complete cycle a gas takes in 500 J of heat from a hot source and 300 J from a second source, and rejects 200 J to a cold sink. The net work done by the gas over the cycle is:
Q26.
Two moles of a monatomic ideal gas are warmed from 300 K to 400 K at constant pressure (R = 8.31 J/mol K). The work done by the gas is about:
Q27.
A Carnot engine rejects heat to a sink at 300 K and runs at 40% efficiency. To lift its efficiency to 50% with the same sink temperature, the source temperature must be raised by:
Q28.
A gas releases 100 J of heat while 40 J of work is done on it. The change in its internal energy is:
Q29.
A gas expands at constant pressure 2 × 10<sup>5</sup> Pa from 2 L to 5 L. The work done by the gas is:
Q30.
2 moles of a monatomic ideal gas are heated at constant volume by 100 K (R = 8.31 J/mol K). The heat supplied is:
Q31.
1 mole of ideal gas at 27 degrees C has internal energy (Cv = 3R/2 for monatomic):
Q32.
An ideal gas expands isothermally. Work done by gas:
Q33.
A Carnot engine has 60% efficiency. If cold reservoir is at 300 K, hot reservoir temperature:
Q34.
For a gas expanding adiabatically, gamma = Cp/Cv = 5/3. If pressure halves, volume changes by factor:
Q35.
Entropy change when 100 J of heat is added to a system at 400 K:
Q36.
Which process has the steepest slope on a P-V diagram?
Q37.
1 kg of water at 100 degrees C converts to steam. Latent heat of vaporization = 2.26 x 10<sup>6</sup> J/kg. Heat required:
Q38.
Heat engine takes 1000 J from hot source, does 400 J of work. Heat rejected to cold reservoir:
Q39.
Mean kinetic energy of a gas molecule at temperature T:
Q40.
RMS speed of gas molecules is proportional to:
Q41.
For an ideal gas, relation between Cp and Cv is:
Q42.
A process in which PV<sup>n</sup> = constant is called:
Q43.
Work done by an ideal gas in an isobaric expansion from V<sub>1</sub> to V<sub>2</sub> at pressure P:
Q44.
Coefficient of performance (COP) of a refrigerator is:
Q45.
At absolute zero (0 K), all molecular motion:
Q47.
Ideal gas at constant temperature has pressure 4 atm and volume 2 L. If pressure becomes 2 atm, volume:
Q48.
In a reversible process, entropy of the universe:
Q49.
Speed of sound in a gas depends on:
Q50.
If temperature of a gas doubles (at constant pressure), its volume:
Q51.
A monatomic ideal gas (γ = 5/3) at 300 K is compressed adiabatically to one-eighth of its original volume. The final temperature is:
Q52.
Two Carnot engines work in series: the first between 800 K and an intermediate temperature T, the second between T and 200 K. If both engines have equal efficiency, T equals:
Q53.
A Carnot engine absorbs 600 J at 400 K and rejects heat to a sink at 300 K. The work it does per cycle is:
Q54.
A heat engine absorbs 800 J per cycle and rejects 320 J to the cold reservoir. Its efficiency is:
Q55.
1 mole of a monatomic ideal gas expands adiabatically as its temperature falls from 400 K to 300 K (R = 8.31). The work done by the gas is about:
Q56.
One mole of ideal gas undergoes cycle: isothermal expansion at T<sub>1</sub>, then cooling to T<sub>2</sub>, then isothermal compression, then heating. This is a:
Q57.
1 mole of diatomic gas (Cv = 5R/2) undergoes isochoric heating from 300K to 600K. Heat added:
Q58.
Carnot efficiency = 80%. If cold reservoir is at 400 K, hot reservoir is at:
Q59.
An ideal gas undergoes free expansion into vacuum (Q=0, W=0). Temperature change:
Q60.
Work done during isothermal expansion of n moles from V<sub>1</sub> to V<sub>2</sub> at temperature T:
Q61.
Entropy change when 0.5 kg of ice melts at 0 degrees C. Latent heat = 336 kJ/kg:
Q62.
For 2 moles of monatomic ideal gas, ratio of work done to heat exchanged in isothermal expansion:
Q63.
COP of a Carnot refrigerator operating between 200 K and 300 K:
Q64.
Mean free path of gas molecules increases when:
Q65.
A heat engine performs 1000 J of work and rejects 1500 J to the cold reservoir. Efficiency:
Q66.
Maxwell-Boltzmann distribution of molecular speeds: most probable speed v<sub>p</sub> compared to rms speed v<sub>rms</sub>:
Q67.
In an Otto cycle, heat is added at:
Q68.
For Van der Waals gas (a, b are constants): (P + an<sup>2</sup>/V<sup>2</sup>)(V - nb) = nRT. At high pressure compared to ideal gas, the gas:
Q69.
Triple point of water is at:
Q70.
Joule-Thomson effect: when a real gas expands through a porous plug at constant enthalpy, temperature:
Q71.
Dulong-Petit law states that molar heat capacity of most metals at room temperature is:
Q72.
Entropy can be expressed as S = k ln(omega) where omega is:
Q73.
A gas expands adiabatically from (P<sub>1</sub>, V<sub>1</sub>) to (P<sub>2</sub>, V<sub>2</sub>). Work done by gas:
Q74.
If a system undergoes a cyclic process, net change in internal energy is:
Q75.
Clausius inequality states: for any process, cyclic integral of dQ/T:
Q76.
A Carnot engine operates between a source at 500 K and a sink at 300 K. Its efficiency is:
Q77.
One mole of an ideal gas (γ = 1.4) is adiabatically compressed to half its volume. The ratio of final to initial temperature is approximately:
Q78.
One mole of an ideal gas expands isothermally from V to 2V at 300 K (R = 8.31 J/mol·K). The work done by the gas is about:
Q79.
A gas absorbs 200 J of heat and does 150 J of work on its surroundings. The change in its internal energy is:
Q80.
In a complete cyclic process a gas absorbs 100 J of heat. The net work done by the gas over the cycle is:
Q81.
For a diatomic ideal gas (rigid molecules) with Cv = 5R/2, the ratio γ = Cp/Cv is:
Q82.
An ideal gas undergoes free expansion into a vacuum inside an insulated container. Its temperature:
Q83.
A refrigerator with coefficient of performance 4 extracts 400 J of heat from the cold reservoir per cycle. The work input required is:
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