BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 3 — Questions and Answers
Question 1: The Gibbs phase rule (F = C - P + 2) determines which of the following?
- Number of phases present at equilibrium
- Degrees of freedom in a multiphase system (Correct answer)
- Gibbs free energy of mixing
- Number of components in a reaction
Correct answer: Degrees of freedom in a multiphase system
The Gibbs phase rule gives the degrees of freedom F (independent intensive variables) for a system with C components and P phases.
Question 2: Which mass transfer operation is best suited to separate a dissolved solid from a liquid solution based on solubility differences at different temperatures?
- Distillation
- Absorption
- Crystallization (Correct answer)
- Extraction
Correct answer: Crystallization
Crystallization exploits the temperature dependence of solubility to selectively precipitate a dissolved solid from solution.
Question 3: In a CSTR (Continuous Stirred Tank Reactor) at steady state, which assumption is always made?
- Plug flow with no axial mixing
- Concentration is uniform throughout the reactor volume (Correct answer)
- Temperature varies along the reactor length
- Reactant conversion is always higher than in a PFR
Correct answer: Concentration is uniform throughout the reactor volume
A CSTR assumes perfect mixing, so the concentration and temperature inside are uniform and equal to the exit stream values.
Question 4: Raoult's law is applicable to which type of liquid mixture?
- Highly non-ideal mixtures with strong intermolecular forces
- Ideal mixtures where component interactions are similar (Correct answer)
- Mixtures near the critical point only
- Immiscible liquid systems
Correct answer: Ideal mixtures where component interactions are similar
Raoult's law (pᵢ = xᵢPᵢ*) applies to ideal solutions where all molecules interact with similar forces regardless of composition.
Question 5: What does the Fanning friction factor measure in pipe flow?
- Ratio of wall shear stress to kinetic energy per unit volume (Correct answer)
- Ratio of turbulent to laminar velocity profiles
- Pressure drop per unit length per unit density
- Viscous dissipation in fittings only
Correct answer: Ratio of wall shear stress to kinetic energy per unit volume
The Fanning friction factor is defined as the ratio of wall shear stress to the fluid's kinetic energy per unit volume (τ_w / (½ρv²)).
Question 6: In process safety, what is the Lower Flammability Limit (LFL) of a gas?
- Minimum temperature for spontaneous ignition
- Minimum fuel concentration in air that supports combustion (Correct answer)
- Maximum pressure before a vessel ruptures
- Lowest heat of combustion of the fuel
Correct answer: Minimum fuel concentration in air that supports combustion
The LFL is the minimum concentration of a flammable vapor in air below which a flame cannot propagate.
Question 7: Which separation technique exploits differences in molecular size by using a semipermeable membrane?
- Liquid-liquid extraction
- Membrane filtration (ultrafiltration/reverse osmosis) (Correct answer)
- Adsorption on activated carbon
- Azeotropic distillation
Correct answer: Membrane filtration (ultrafiltration/reverse osmosis)
Membrane filtration processes such as reverse osmosis and ultrafiltration separate species based on molecular size using semipermeable membranes.
BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 3
The Gibbs phase rule (F = C - P + 2) determines which of the following?