Free Chemical Engineering Thermodynamics MCQs with Answers

• A. Adiabatic compression
• B. Isothermal expansion
• C. Adiabatic expansion
• D. Isothermal compression

Explanation: During adiabatic compression, no heat enters, so work done on the system raises its internal energy and temperature.

• A. Supersaturated
• B. Superheated
• C. Both A. and B
• D. Neither A. nor B

Explanation: Adiabatic compression of saturated vapour increases its temperature while entropy remains approximately constant, moving the state into…

• A. Carnot engine
• B. Heat engine
• C. Heat pump
• D. None of these

Explanation: A refrigerator is a heat pump operated to remove heat from a low-temperature space and reject it to the surroundings.

• A. More in vapour phase
• B. More in liquid phase
• C. Replaced by chemical potential which is more in vapour phase
• D. Same in both the phases

Explanation: At phase equilibrium, there is no driving force for transfer of the component between phases, so its chemical potential, equal to its…

• A. Increases
• B. Decreases
• C. Remain constant
• D. Increases linearly

Explanation: For an ideal Otto cycle, efficiency is η = 1 − 1/r^(γ−1), where r is the compression ratio and γ is greater than one.

• A. Reversible isothermal
• B. Reversible adiabatic
• C. Irreversible isothermal
• D. None of these

Explanation: A reversible adiabatic process has no entropy transfer by heat and no entropy generation, so its entropy remains constant and it is called…

• A. (∂E/∂ni)S, v, nj
• B. (∂G/∂ni)T, P, nj = (∂A/∂ni) T, v, nj
• C. (∂H/∂ni)S, P, nj
• D. All (A), B. and (C)

Explanation: From the fundamental thermodynamic relations, μᵢ equals the partial derivative of E at constant S,V, the partial derivative of G at…

• A. None of these
• B. Chemical potentials of all components should be same in a particular phase
• C. Sum of the chemical potentials of any given component in all the phases should be the same
• D. Chemical potentials of a given component should be equal in all phases

Explanation: Phase equilibrium requires equality of the chemical potential of each component in every phase: μᵢ^α = μᵢ^β = ... .

• A. A combination of separating & throttling
• B. Throttling
• C. Separating
• D. Bucket

Explanation: A separating calorimeter removes entrained water before the steam is tested, making it suitable for wet steam with a very low dryness…

• A. Cold reservoir approaches zero
• B. Either A. or B
• C. Hot reservoir approaches infinity
• D. Neither A. nor B

Explanation: Carnot efficiency is η = 1 − Tc/Th, so it approaches unity if the cold-reservoir temperature approaches absolute zero or the hot-reservoir…

• A. None of these
• B. Unity
• C. Infinity
• D. Zero

Explanation: For Helmholtz free energy, (∂F/∂T)V = −S. As temperature approaches absolute zero, the entropy approaches zero according to the third law…

• A. Work done under isothermal condition
• B. Work done under adiabatic condition
• C. Compressibility
• D. Co-efficient of thermal expansion

Explanation: For reversible isothermal expansion of an ideal gas, W = nRT ln(V2/V1).

• A. Vary as square of the absolute temperature
• B. Are more or less constant (vary from 0.2 to 0.3)
• C. Vary as square of the absolute pressure
• D. None of these

Explanation: The critical compressibility factor, Zc = PcVc/(RTc), is approximately similar for many substances and commonly lies around 0.2 to 0.3.

• A. Pressure
• B. Temperature
• C. Both A. & B
• D. Neither A. nor B

Explanation: For an ideal gas, entropy changes according to both temperature and pressure, for example Δs = Cp ln(T2/T1) − R ln(P2/P1).

• A. -ve
• B. +ve
• C. Zero
• D. Dependent on the path

Explanation: Internal energy is a state function, so its change depends only on the initial and final states.

• A. Direction of energy transfer
• B. Amount of energy transferred
• C. Irreversible processes only
• D. Non-cyclic processes only

Explanation: The first law accounts for the amount of energy transferred, whereas the second law determines its direction and whether a process is…

• A. First law
• B. Zeroth law
• C. Third law
• D. Second law

Explanation: The zeroth law establishes thermal equilibrium and provides the basis for defining and measuring temperature, a fundamental thermodynamic…

• A. Becomes zero
• B. Equals 1 kcal/kmol °K
• C. Becomes infinity
• D. Equals 0.24 kcal/kmol °K

Explanation: At the critical point, large fluctuations in fluid properties cause the constant-pressure heat capacity, Cp, to diverge theoretically…

• A. Not have a sub-atmospheric vapour pressure at the temperature in the refrigerator coils
• B. Not have unduly high vapour pressure at the condenser temperature
• C. Have low specific heat
• D. Both A. and B

Explanation: A practical refrigerant should have a vapor pressure above atmospheric pressure in the evaporator, avoiding air leakage, but should not…

• A. dP/dT = ΔH/TΔV
• B. ln P = - (ΔH/RT) + constant
• C. ΔF = ΔH + T [∂(ΔF)/∂T]P
• D. None of these

Explanation: The integrated Clausius-Clapeyron relation for vaporization is ln P = -ΔH/(RT) + constant, assuming approximately constant latent heat and…