Question 1

Reversibility of basic thermodynamic processes: evaluate the statement  Statement: “The constant-pressure, constant-volume, and general p·vⁿ processes are regarded as irreversible processes.” Decide whether this statement is correct.

Accepted Answer

Concept/ApproachA process type (isobaric, isochoric, polytropic p·vⁿ) can be carried out reversibly or irreversibly depending on how it is executed (quasi-static with negligible gradients vs. finite gradients, friction, etc.).Thus, none of these process labels inherently implies irreversibility.Final AnswerDisagree — the statement is incorrect.

Question 2

Fuels: name the process—coal strongly heated for 42–48 hours in a closed vessel without air  Identify the standard term for this process used to produce coke and by-products.

Accepted Answer

Concept/ApproachProlonged heating of coal in absence of air in a retort/oven produces coke, tar, gas, etc.; this is called carbonization (also termed destructive distillation).Final AnswerCarbonization (destructive distillation) of coal

Question 3

First law at constant volume: decide correctness of the statement  Statement: “When a gas is heated at constant volume, the heat supplied increases the internal energy of the gas.”

Accepted Answer

Concept/ApproachAt constant volume, boundary work is zero: W = ∫ p dV = 0.First law: Q = ΔU + W ⇒ Q = ΔU. Heat supplied raises internal energy.Final AnswerAgree — the heat at constant volume increases internal energy.

Question 4

Otto cycle on a T–s (temperature–entropy) diagram: choose the correct description  Identify the correct schematic description of how the Otto cycle appears on a T–s plot.

Accepted Answer

Concept/ApproachOtto cycle: isentropic compression → constant-volume heat addition → isentropic expansion → constant-volume heat rejection.On a T–s diagram: isentropes are vertical lines; constant-volume processes appear as sloped curves (entropy changes with temperature at v = const).Final AnswerTwo vertical (isentropic) lines joined by two constant-volume heat-addition/rejection curves.

Question 5

Internal energy change in an isothermal process: evaluate the statement  Statement: “There is no change in internal energy in an isothermal process.” Decide whether this is correct for an ideal gas.

Accepted Answer

Concept/ApproachFor an ideal gas, internal energy depends only on temperature: ΔU = m cv ΔT.Isothermal ⇒ ΔT = 0 ⇒ ΔU = 0.Final AnswerAgree — for an ideal gas, isothermal implies no change in internal energy.

Question 6

Liquid fuels: identify the lightest and most volatile common liquid fuel  Choose the fuel that is lightest and most volatile among the listed options.

Accepted Answer

Concept/ApproachVolatility decreases from gasoline → kerosene → diesel → heavy fuel oils. Gasoline has the lowest boiling range and highest volatility.Final AnswerPetrol (gasoline)

Question 7

Stoichiometry: oxygen required for CO to CO₂ conversion  Reaction: CO + (1/2) O₂ → CO₂. For 1 kg of CO producing 11/7 kg of CO₂, compute the required mass of O₂ (in kg). Choose the correct value.

Accepted Answer

Given/ReactionCO + (1/2) O₂ → CO₂Molar masses: CO = 28, O₂ = 32, CO₂ = 44 (kg per kmol).Step-by-step calculation28 kg CO needs (1/2)×32 = 16 kg O₂ and forms 44 kg CO₂.Per 1 kg CO: O₂ required = 16/28 = 4/7 kg; CO₂ formed = 44/28 = 11/7 kg (matches the statement).Final Answer4/7 kg of O₂

Question 8

Atomic masses: identify the element with the smallest atomic mass among the given choices  Compare standard atomic masses at natural isotopic abundance for Oxygen, Sulphur, Nitrogen, and Carbon. Choose the correct option.

Accepted Answer

Given dataApproximate standard atomic masses (u): O ≈ 16, S ≈ 32, N ≈ 14, C ≈ 12.Concept/ApproachAtomic mass reflects the weighted average mass of naturally occurring isotopes. To find the minimum, compare the known approximate values.Step-by-step checkCompare: 12 (C) Common pitfallsDo not confuse atomic number with atomic mass; also, sulphur's mass is roughly double oxygen's.Final AnswerCarbon

Question 9

Carbonisation of coal: identify the correct description of the process  Select the statement that correctly defines carbonisation of coal (coke-making by heating coal in the absence of air). Choose the correct option.

Accepted Answer

ConceptCarbonisation of coal (coking) is the strong heating of coal in the absence of air to drive off volatiles and obtain coke. The options given describe other operations:(a) Pulverisation (size reduction), not carbonisation.(b) Briquetting (agglomeration), not carbonisation.(c) Refers to wood (charcoal making) at relatively low temperature; the question is about coal.Final AnswerNone of the above

Question 10

Avogadro’s law and gas density: proportionality with molecular mass  For two gases at the same temperature and pressure, state how their densities compare with their molecular masses. Choose the correct relationship.

Accepted Answer

ConceptAt the same T and p, Avogadro’s law implies equal molar volumes. Density ρ is ρ = (mass)/(volume) = (M molar mass)/(molar volume). With constant molar volume, ρ ∝ M.Stepρ1/ρ2 = M1/M2Final AnswerDirectly proportional to molecular mass

Question 11

Entropy in an irreversible cyclic process: behavior over one complete cycle  Evaluate how the entropy of the system changes over a full irreversible cycle. Choose the correct statement.

Accepted Answer

ConceptEntropy (S) is a state function. For any complete cycle (start and end at the same state), the change in entropy of the system is zero: ΔSsystem = 0, even if the processes are irreversible.Important nuanceClausius inequality gives ∮ δQ/T for an irreversible cycle, but this integral is not equal to ΔSsystem over the cycle (which is zero by definition of a state function). The inequality reflects entropy generation in surroundings/universe, not a net change of the system after completing the loop.Common pitfallsMixing up entropy of the system with entropy of the universe. The latter increases for overall spontaneous irreversible processes.Final AnswerRemains constant over the cycle

Question 12

Adiabatic process: identify the correct defining properties  An adiabatic process for a gas is characterized by no heat transfer; infer its implications for temperature and energy balance. Choose the correct option.

Accepted Answer

ConceptAdiabatic process: Q = 0. From the first law, ΔU = Q − W (sign convention: W is work done by the system). With Q = 0, ΔU = −W (or equivalently, the change in internal energy equals the negative of work by the system; equals work on the system). Temperature generally changes when a gas compresses/expands adiabatically.Why all are true(a) is the definition; (b) typically occurs in adiabatic expansion/compression; (c) follows directly from the first law with Q = 0.Final AnswerAll of the above

Question 13

Pressure units conversion: value of 1 mm of mercury in SI units (N/m²)  Convert a pressure head of 1 mm Hg to pascals (N/m²) using the standard definition. Choose the correct value.

Accepted Answer

ConceptStandard atmospheric pressure: 760 mm Hg ≈ 101325 Pa. Therefore,Calculation1 mm Hg ≈ 101325 / 760 Pa≈ 133.322 Pa ≈ 133.3 N/m²Final Answer133.3 N/m²

Question 14

Diesel vs. Otto cycle efficiency: limiting behavior with cut-off ratio  State when the Diesel cycle efficiency approaches the Otto cycle efficiency. Choose the correct condition.

Accepted Answer

ConceptDiesel cycle has heat addition at constant pressure with a finite cut-off ratio rc. As rc → 1 (i.e., cut-off → 0), the Diesel cycle heat addition tends to constant volume, and the cycle approaches the Otto cycle.Final AnswerCut-off is zero

Question 15

Kinetic theory statement: kinetic energy at absolute zero  Evaluate the statement: “The kinetic energy of gas molecules becomes zero at absolute zero temperature (0 K).” Choose the correct option.

Accepted Answer

ConceptFor an ideal gas, the average translational kinetic energy per molecule is (3/2) k T. At T = 0 K, this expression gives zero kinetic energy.NoteQuantum zero-point energy exists in real systems, but the ideal-gas kinetic theory model used in basic thermodynamics treats the average kinetic energy as proportional to T.Final AnswerTrue

Question 16

Kinetic theory relation: pressure vs. kinetic energy density for an ideal gas  Complete the statement: The pressure exerted by an ideal gas equals what fraction of the kinetic energy of all molecules per unit volume? Choose the correct fraction.

Accepted Answer

ConceptKinetic theory yields p = (2/3) × (total translational kinetic energy per unit volume). Equivalently, the kinetic energy density is (3/2) p.Derivation sketchFrom molecular impacts on walls and isotropic velocity distribution, p = (1/3) ρ c2, and kinetic energy density is (1/2) ρ c2. Ratio: p / (KE density) = (1/3) / (1/2) = 2/3.Final Answertwo-third

Question 17

Thermodynamic property: identify U + p·v  Select the thermodynamic property defined as the sum of internal energy (U) and the product of pressure and volume (p·v). Choose the correct option.

Accepted Answer

ConceptEnthalpy is defined as H = U + p v. It is especially convenient for open systems (flow processes) at approximately constant pressure, where enthalpy changes track heat transfer.Why others are incorrectWork is a path function; entropy (S) is a different state function relating heat transfer and temperature.Final Answerenthalpy

Question 18

First law of thermodynamics: judge the correctness of the statement  Statement: “In the first law of thermodynamics, the total energy of the system remains constant.”  Choose whether the statement is correct or incorrect.

Accepted Answer

Concept/ApproachThe first law is an energy balance: the change in a system's total energy equals heat added minus work done by the system.It does not say the system's energy is always constant; only an isolated system (Q = W = 0) keeps constant energy.Key relationΔE = Q − WE includes U (internal), KE, and PE.ExampleAt constant volume heating: W = 0 ⇒ ΔE = Q > 0, so energy increases.Final AnswerDisagree — the system's energy need not remain constant; it changes per ΔE = Q − W.

Question 19

Specific heats for an ideal gas: compare cp and cv  State how the specific heat at constant pressure (cp) compares to the specific heat at constant volume (cv).  Choose the correct comparison.

Accepted Answer

Concept/ApproachAt constant pressure, part of the heat goes into doing boundary work during expansion; hence more heat per kelvin is required.For an ideal gas: cp − cv = R and the ratio γ = cp/cv > 1.Final Answercp is greater than cv.

Question 20

Identify the air-standard cycle from its process set  Processes: one constant-pressure process, one constant-volume process, and two isentropic (reversible adiabatic) processes.  Choose the correct cycle name.

Accepted Answer

Concept/ApproachDiesel cycle: isentropic compression → constant-pressure heat addition → isentropic expansion → constant-volume heat rejection.Otto: two isentropes + two constant-volume processes.Carnot: two isotherms + two isentropes. Stirling: two isotherms + two constant-volume processes with regeneration.Final AnswerDiesel cycle

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