Q.1 Which of the following is a state function in thermodynamics?
Work
Heat
Internal Energy
Path taken
Explanation - Internal energy depends only on the initial and final states of the system, not on the path followed. Heat and work are path functions.
Correct answer is: Internal Energy
Q.2 First law of thermodynamics is based on the principle of:
Entropy
Conservation of mass
Conservation of energy
Irreversibility
Explanation - The first law states that energy can neither be created nor destroyed; it can only change from one form to another.
Correct answer is: Conservation of energy
Q.3 In an isothermal process, the internal energy of an ideal gas:
Increases
Decreases
Remains constant
Becomes zero
Explanation - For an ideal gas, internal energy depends only on temperature. In isothermal processes, temperature remains constant, so internal energy does not change.
Correct answer is: Remains constant
Q.4 The unit of entropy in SI system is:
J/kg
J/K
J/mol
J
Explanation - Entropy is defined as the ratio of heat transfer to temperature (ΔS = Q/T), so its SI unit is joule per kelvin (J/K).
Correct answer is: J/K
Q.5 Which process has zero change in enthalpy?
Isothermal
Adiabatic
Isochoric
Isobaric
Explanation - In an adiabatic process, no heat is exchanged. For a reversible adiabatic process, enthalpy change is zero in case of ideal gases.
Correct answer is: Adiabatic
Q.6 Which thermodynamic quantity is an extensive property?
Pressure
Temperature
Entropy
Density
Explanation - Extensive properties depend on the amount of substance. Entropy is proportional to the system size, unlike temperature or pressure.
Correct answer is: Entropy
Q.7 In a cyclic process, the change in internal energy is:
Positive
Negative
Zero
Infinite
Explanation - Since the system returns to its initial state in a cyclic process, all state functions including internal energy return to their initial values.
Correct answer is: Zero
Q.8 The efficiency of a Carnot engine depends on:
Working substance
Heat rejected
Temperature of reservoirs
Pressure applied
Explanation - The efficiency of a Carnot engine depends only on the temperatures of the hot and cold reservoirs, η = 1 - Tc/Th.
Correct answer is: Temperature of reservoirs
Q.9 During an isobaric expansion of an ideal gas, which of the following is true?
Work done is zero
Temperature remains constant
Internal energy changes
No heat is absorbed
Explanation - In isobaric expansion, pressure is constant but volume increases. Hence temperature rises, causing a change in internal energy.
Correct answer is: Internal energy changes
Q.10 In thermodynamics, 'reversible process' means:
Process is very fast
Process can be reversed without leaving changes in system and surroundings
No heat exchange
Work done is zero
Explanation - A reversible process is an idealized process that can be reversed infinitely slowly with no net effect on the system and surroundings.
Correct answer is: Process can be reversed without leaving changes in system and surroundings
Q.11 What does the second law of thermodynamics imply about natural processes?
They are always reversible
Entropy of universe decreases
Entropy of universe increases
Work done is zero
Explanation - The second law states that the entropy of the universe tends to increase for all natural processes.
Correct answer is: Entropy of universe increases
Q.12 In a PV diagram, the work done by the gas is represented by:
Area under the curve
Slope of the curve
Intercept on pressure axis
Intercept on volume axis
Explanation - Work done by a gas in a PV diagram is given by the area under the pressure-volume curve.
Correct answer is: Area under the curve
Q.13 A process at constant volume is called:
Isothermal
Isobaric
Isochoric
Adiabatic
Explanation - When volume is constant, the process is known as isochoric. No work is done in this case (W = 0).
Correct answer is: Isochoric
Q.14 If a gas expands adiabatically, then:
Heat is supplied
Heat is rejected
No heat exchange
Temperature remains constant
Explanation - In adiabatic processes, there is no exchange of heat with the surroundings (Q = 0).
Correct answer is: No heat exchange
Q.15 Which of the following has the highest efficiency theoretically?
Otto cycle
Diesel cycle
Carnot cycle
Brayton cycle
Explanation - Carnot cycle is an ideal reversible cycle that gives the maximum possible efficiency between two temperature reservoirs.
Correct answer is: Carnot cycle
Q.16 The specific heat capacity at constant volume for a monoatomic ideal gas is:
R
3R/2
5R/2
2R
Explanation - For a monoatomic ideal gas, Cv = (3/2)R, where R is the universal gas constant.
Correct answer is: 3R/2
Q.17 For an isothermal reversible process of an ideal gas, ΔU is:
Zero
Positive
Negative
Infinity
Explanation - Internal energy of an ideal gas depends only on temperature. Since temperature is constant in isothermal processes, ΔU = 0.
Correct answer is: Zero
Q.18 The maximum work that can be obtained from a heat engine is determined by:
First law
Second law
Third law
Zeroth law
Explanation - The second law of thermodynamics sets the maximum limit for efficiency of heat engines, thus deciding the maximum possible work.
Correct answer is: Second law
Q.19 If Cp and Cv are molar specific heats, then Cp - Cv equals:
R
2R
R/2
Zero
Explanation - Mayer’s relation states that Cp - Cv = R for an ideal gas.
Correct answer is: R
Q.20 The third law of thermodynamics deals with:
Entropy at absolute zero
Energy conservation
Direction of heat flow
Work done in cyclic process
Explanation - The third law states that the entropy of a pure crystalline substance approaches zero as temperature approaches absolute zero.
Correct answer is: Entropy at absolute zero
Q.21 Which of the following processes is most efficient in converting heat to work?
Reversible isothermal process
Irreversible process
Reversible adiabatic process
Reversible cyclic process
Explanation - A reversible cyclic process like the Carnot cycle converts heat into work with maximum efficiency allowed by the second law.
Correct answer is: Reversible cyclic process
Q.22 Latent heat of fusion of ice is:
80 cal/g
540 cal/g
100 cal/g
20 cal/g
Explanation - The latent heat of fusion of ice is approximately 80 cal/g or 334 J/g.
Correct answer is: 80 cal/g
Q.23 Which of the following is true for an isothermal reversible expansion of an ideal gas?
Q = 0
ΔU = 0
W = 0
ΔS = 0
Explanation - In isothermal processes for an ideal gas, internal energy remains constant, hence ΔU = 0.
Correct answer is: ΔU = 0
Q.24 A heat engine rejects 200 J of heat and absorbs 500 J of heat. The efficiency is:
20%
40%
50%
60%
Explanation - Efficiency η = W/Q1 = (Q1 - Q2)/Q1 = (500 - 200)/500 = 300/500 = 0.6 or 60%.
Correct answer is: 60%
Q.25 The relation between pressure, volume, and temperature is given by:
Boyle’s law
Charles’ law
Ideal gas equation
Gay-Lussac’s law
Explanation - The ideal gas equation PV = nRT relates pressure, volume, and temperature of an ideal gas.
Correct answer is: Ideal gas equation