Free Chemical Engineering Thermodynamics MCQs with Answers

• A. 0
• B. ∞
• C. 0.5
• D. 1

Explanation: Dryness fraction is the mass fraction of vapour in a wet-steam mixture.

• A. Isothermal expansion
• B. Isochoric heat addition
• C. Polytropic expansion
• D. Isobaric heat addition

Explanation: During reversible isothermal expansion of an ideal gas, entropy increases as the gas expands, while its temperature and internal energy…

• A. Volume
• B. Pressure
• C. Heat
• D. None of these

Explanation: In the ideal Otto cycle, heat is supplied at constant volume, so it is called the constant-volume or constant-space cycle.

• A. Pressure change to temperature change occuring during adiabatic compression of a gas
• B. Temperature change to pressure change occuring during adiabatic throttling of a gas
• C. Temperature change to pressure change occuring during adiabatic compression of a gas
• D. Pressure change to temperature change occuring during adiabatic throttling of a gas

Explanation: The Joule-Thomson coefficient is μJT = (∂T/∂P)H, measured during throttling, which is normally adiabatic and isenthalpic.

• A. Decreases with the increase of concentration of the solute
• B. Increases with the increase of concentration of the solute
• C. Is unity at infinite dilution
• D. Remains constant

Explanation: In a sufficiently dilute solution, the solute activity coefficient is approximately independent of concentration, so it is treated as…

• A. Entropy
• B. Enthalpy
• C. Internal energy
• D. Temperature

Explanation: Compression within the elastic range is treated as reversible, and an adiabatic reversible process is isentropic.

• A. -R ln 2
• B. R ln 2
• C. 3 R ln 2
• D. -3R ln 2

Explanation: For an ideal equimolar binary mixture, the molar entropy of mixing is -R[xA ln xA + xB ln xB] = -R[2(0.5 ln 0.5)] = R ln 2.

• A. 1.5
• B. 1.4
• C. 1
• D. Y = Cp/Cv

Explanation: For compression between the same initial and final states, isothermal compression, n = 1, requires the least work because heat is removed…

• A. 273.15
• B. 225.65
• C. 100.03
• D. 373.15

Explanation: Latent heat becomes zero at the critical point of water, whose pressure is about 22.06 MPa.

• A. ΔQ = 0, ΔS=0
• B. ΔQ = 0, ΔS = +ve
• C. ΔQ = 0, ΔS = -ve
• D. ΔQ = +ve, ΔS= +ve

Explanation: For the intended free, totally irreversible expansion, no work is done and an ideal gas has unchanged internal energy, so Q is zero; its…

• A. 230 J
• B. 4600 J
• C. 2300 J
• D. 2.3 x 10^6 J

Explanation: The heat removed is nCpΔT = 1 × 23 × (400 − 300) = 2300 J. Cooling releases this amount, so the magnitude of heat released is 2300 J.

• A. Wet
• B. Saturated
• C. None of these
• D. Superheated

Explanation: A throttling valve is isenthalpic, so the steam retains the enthalpy of dry saturated steam at 25 kg/cm².

• A. Heat addition & compression ratio
• B. Heat addition & pressure
• C. Compression ratio & pressure
• D. Cylinder dimension & rpm

Explanation: For equal compression ratio and equal heat supplied, the Otto cycle has constant-volume heat addition, which gives a higher average…

• A. +4000
• B. -4000
• C. 10000
• D. -10000

Explanation: Using the first law with work done on the gas, ΔU = heat added + work on gas = -3000 + 7000 = +4000 kJ.

• A. Consumer minimum horse power
• B. Has very high C.O.P.
• C. Employs minimum quantity of refrigerant
• D. Is as light as possible

Explanation: Aircraft refrigeration systems must minimize weight because every additional kilogram increases the aircraft's fuel consumption and…

• A. R
• B. -R
• C. 0
• D. (3/2) R

Explanation: For an ideal gas, the Mayer relation gives Cp - Cv = R, where R is the universal or specific gas constant as appropriate.

• A. Carbon dioxide
• B. Water
• C. Mercury
• D. None of these

Explanation: Water is anomalous: its solid form, ice, is less dense than liquid water because hydrogen bonding creates an open crystal structure.

• A. Increases & decreases
• B. Increases & increases
• C. Decreases & increases
• D. Decreases & decreases

Explanation: Throttling is isenthalpic, and when wet steam expands to a lower pressure its saturation temperature falls while its dryness fraction…

• A. 30,000 J
• B. 60,000 J
• C. 90,000 J
• D. 2,40,000 J

Explanation: The reaction extent is limited by calcium: 2 mol Ca allows 2 mol of reaction, while 3 mol carbon allows 1.5 mol, so carbon is limiting.

• A. Passing it through a pressure reducing valve
• B. Increasing its cross-sectional area of flow
• C. Forcing it downwards through a vertical tube
• D. None of these

Explanation: A pressure-reducing valve produces throttling, in which enthalpy remains approximately constant.