Thermodynamics — Previous-Year Questions

Q1. Ideal gas isothermal expansion from V to 2V at 300 K, n = 1 mol. Work done:

Q2. ΔU for an ideal gas in an isothermal process:

Q3. On a PV diagram, isothermal curve is:

Q4. During isothermal compression, heat:

Q5. For isothermal expansion: Q vs W relation:

Q1. Adiabatic compression of monatomic gas (γ = 5/3) from V to V/2. T_f/T_i:

Q2. In an adiabatic process for an ideal gas, Q is:

Q3. Adiabatic curve on PV diagram is:

Q4. Sudden compression of air in a hand pump: gas heats up because:

Q5. Adiabatic expansion of an ideal gas: temperature:

Q1. Work done in an isochoric process:

Q2. In an isochoric process for an ideal gas, heat absorbed equals:

Q3. If T doubles at constant V, pressure:

Q4. Isochoric process on a PV diagram:

Q5. For an isochoric process: Q = nC_vΔT because:

Q1. 2 mol of an ideal gas at constant P = 100 kPa expanded from 0.02 to 0.05 m³. Work done by gas:

Q2. Isobaric process on PV diagram:

Q3. Q = nC_pΔT for an isobaric process because:

Q4. Doubling absolute T at constant P doubles:

Q5. For an isobaric process: Q − ΔU equals:

Q1. A gas absorbs 200 J of heat and does 100 J of work. ΔU:

Q2. First law of thermodynamics is essentially:

Q3. An ideal gas undergoes ISOTHERMAL expansion absorbing 500 J. Work done by gas:

Q4. Free expansion of an ideal gas into vacuum: ΔU and ΔT?

Q5. If 100 J of work is done ON the system and no heat is exchanged, ΔU is:

Q1. Work done by gas during ISOCHORIC process:

Q2. Ideal gas (n = 2 mol) expands isobarically at P = 1 atm from 1 L to 3 L. Work:

Q3. Same ideal gas (2 mol at 300 K) isothermal expansion from V to 2V. Work:

Q4. Work done is PATH-dependent, but ΔU is:

Q5. Net work over a cycle equals:

Q1. Heat engine takes 500 J from hot reservoir and dumps 350 J to cold. Efficiency:

Q2. Real engine efficiency vs Carnot efficiency:

Q3. Heat engine cannot convert 100% heat to work because:

Q4. Maximum efficiency between T_h = 600 K and T_c = 300 K:

Q5. Why do cars have a radiator?

Q1. A refrigerator extracts 200 J from cold and dumps 250 J to hot. Work input:

Q2. Carnot refrigerator COP between 250 K and 300 K:

Q3. Coefficient of performance of a refrigerator can be:

Q4. Heat pump for heating with COP_ref = 3:

Q5. Clausius statement of 2nd law:

Q1. Carnot engine works between 600 K and 300 K. Efficiency:

Q2. If T_cold is doubled (T_hot fixed), Carnot efficiency:

Q3. Can a Carnot engine have 100% efficiency?

Q4. Carnot engine absorbs 1000 J from hot reservoir at 500 K and exhausts to 300 K cold reservoir. Work done:

Q5. Carnot's theorem states:

Q1. An engine has efficiency 30% between T_h = 500 K and T_c = 300 K. Compared to Carnot:

Q2. An engine claims 60% efficiency between 500 K and 300 K. Verdict:

Q3. Why are real engines less efficient than Carnot?

Q4. Combined-cycle power plants achieve ~60% efficiency by:

Q5. Carnot's theorem says:

Q1. On a PV diagram, isothermal curve is a:

Q2. Area under PV curve from V_i to V_f represents:

Q3. Comparing adiabatic and isothermal curves through the same initial point: adiabatic is:

Q4. On a PV cycle, area enclosed equals:

Q5. Isobaric process on PV diagram is a:

Q1. On a TS diagram, an isothermal process is:

Q2. Reversible adiabatic (isentropic) process on TS diagram:

Q3. Area enclosed by a cycle on TS diagram represents:

Q4. Carnot cycle on a TS diagram looks like:

Q5. Carnot efficiency from TS rectangle:

Q1. For a cyclic process: ΔU and Q_net:

Q2. Area enclosed by a cyclic process on PV diagram represents:

Q3. Clockwise cycle on PV diagram represents:

Q4. Efficiency of a heat engine: η =

Q5. Counter-clockwise cycle:

Q1. Internal energy of 1 mole of monatomic ideal gas at 300 K:

Q2. If U of an ideal gas depends only on T, what happens during a free expansion (no work, no heat)?

Q3. C_v for a diatomic ideal gas at room T:

Q4. Internal energy is a:

Q5. C_p − C_v for any ideal gas (Mayer's relation):