All Free Chemical Engineering MCQs with Answers

• A. Reflux ratio
• B. Thermal condition of the feed
• C. Plate efficiency to be achieved
• D. Relative volatility

Explanation: The q-line represents the feed condition, and its slope is q/(q−1). Thus, the slope is fixed by the feed's thermal condition, such as…

• A. Concentrated solutions
• B. Gaseous solutions at high pressure
• C. Dilute solutions, over a small concentration range
• D. None of these

Explanation: The Freundlich equation is an empirical adsorption relation that is most useful for dilute solutions over a limited concentration range.

• A. M(Xo - XF)
• B. M(Xo/XF)
• C. M ln(Xo/XF)
• D. MXo ln(Xo/XF)

Explanation: With the critical moisture equal to Xo, the falling-rate drying rate is Rc(X/Xo).

• A. Multi-component distillation
• B. Gas absorption with chemical reaction
• C. Gas absorption without chemical reaction
• D. Binary distillation

Explanation: The Hatta number compares the rate of a chemical reaction in the liquid film with the rate of diffusion through that film.

• A. Use steam distillation
• B. Use molecular distillation
• C. An azeotrope may be formed during distillation
• D. Use high pressure distillation

Explanation: A low relative volatility means the components have similar vapour pressures and are difficult to separate by ordinary distillation; such…

• A. Continuous
• B. Steam
• C. Flash
• D. Differential

Explanation: Rayleigh's equation describes differential or batch distillation, where the still liquid composition changes continuously as vapour is…

• A. None of these
• B. Increases
• C. Remains unchanged
• D. Decreases

Explanation: For most liquid-liquid extraction systems, increasing temperature increases mutual solubility and shrinks the two-phase region enclosed by…

• A. All A., B. & C.
• B. Foaming
• C. Weeping & dumping
• D. Entrainment

Explanation: Entrainment, foaming, and weeping or dumping all cause poor vapour-liquid contact or bypassing on trays.

• A. 25
• B. > 25
• C. < 25
• D. - 25

Explanation: Heating at constant pressure while keeping the humidity ratio fixed raises the corresponding adiabatic saturation, or wet-bulb…

• A. transfer operations.
• B. Sherwood number in mass transfer is analogous to Nusselt number in heat transfer
• C. Prandtl number in heat transfer is analogous to Schmidt number in mass transfer
• D. Reynolds number in mass transfer is analogous to Grashoff number in heat transfer
• E. Reynolds number remains the same in both heat and mass transfer

Explanation: The usual analogies are Sherwood to Nusselt, Schmidt to Prandtl, and Reynolds to Reynolds.

• A. Azeotropic
• B. Extractive
• C. Steam
• D. Molecular

Explanation: Ethanol and water form an azeotrope, so ordinary fractional distillation cannot achieve complete dehydration.

• A. Ponchon-Savarit method
• B. Tray to tray calculations
• C. Enthalpy concentration method
• D. McCabe-Thiele method

Explanation: Multicomponent distillation requires component-by-component material balances and equilibrium calculations from tray to tray.

• A. Sieve-plate column
• B. Bubble-cap plate column
• C. Packed tower
• D. Wetted wall column

Explanation: Packing breaks the liquid into a thin film over a large wetted area, providing greater vapour-liquid contact area than ordinary trays or a…

• A. Schmidt number
• B. Sherwood number
• C. Lewis relationship
• D. Froude number

Explanation: The Schmidt and Sherwood numbers are directly associated with mass-transfer diffusion and convection, and the Lewis relationship connects…

• A. All A , B & C.
• B. Increasing the rate of extraction
• C. Maintaining the concentration difference between the two phases
• D. Reducing the axial mixing

Explanation: Baffles and horizontal plates suppress axial mixing, promote repeated contact between the phases, and help preserve the concentration…

• A. Continuous
• B. Steam
• C. Azeotropic
• D. None of these

Explanation: Steam distillation is suitable for high-boiling, heat-sensitive materials because steam lowers the mixture’s boiling temperature, allowing…

• A. Evaporation
• B. Adsorption
• C. Dehydration
• D. Sublimation

Explanation: In freeze drying, water is first frozen and then removed under vacuum by direct conversion of ice to vapour.

• A. Used for multi-component systems like crude refining
• B. Same as differential distillation
• C. Same as simple distillation
• D. Most useful for handling binary systems

Explanation: Flash distillation is a single-stage equilibrium separation in which part of a feed vaporises suddenly, and it is especially useful for…

• A. The partial pressure of water vapour increases
• B. The relative humidity decreases
• C. The relative humidity increases
• D. The specific humidity decreases

Explanation: At constant pressure without adding moisture, the water-vapour partial pressure and humidity ratio remain approximately constant, while…

• A. Penetration
• B. Film
• C. Surface renewal
• D. None of these

Explanation: Danckwerts proposed the surface-renewal theory, which treats turbulent eddies as continually replacing elements of liquid at the…