COREN Engineering Practice Exam — Chemical Engineering Specialisation (Nigeria)

For a binary mixture at vapor-liquid equilibrium, what is the fundamental criterion for phase equilibrium in terms of fugacity?

• AThe fugacities of each component in both phases must be equal.
• BThe sum of the fugacities of all components in the liquid phase must equal that in the va…
• CThe fugacity coefficient of each component must equal its activity coefficient.
• DThe fugacity of the mixture in the vapor phase must be zero.

What does the Gibbs-Duhem equation describe regarding the chemical potentials of components in a mixture at constant temperature and pressure?

• AThe sum of the chemical potentials of all components must be zero.
• BThe change in chemical potentials of components are mutually dependent.
• CThe chemical potentials of all components must be equal.
• DThe chemical potential of a component is independent of the composition.

Which of the following equations correctly expresses the relationship between the standard Gibbs free energy change of a reaction and its equilibrium constant?

• ADelta G° = -R T ln K
• BDelta G° = R T ln K
• CDelta G° = -R T K
• DDelta G° = -ln K / (R T)

In a steady-state open system with one inlet and one outlet, how is the first law of thermodynamics represented under negligible kinetic and potential energy changes?

• AQ + W = Delta H
• BQ - W = Delta U
• CQ + W = Delta U
• DQ - W = Delta H

According to the Second Law of Thermodynamics, what must be the entropy change of the universe for any real, irreversible process?

• AIt must be equal to zero.
• BIt must be less than zero.
• CIt must be greater than zero.
• DIt remains constant.

How is the compressibility factor (Z) defined, and what is its value for an ideal gas?

• AZ = P V / (R T); Z = 1
• BZ = P R / (V T); Z = 0
• CZ = V / (P R T); Z = 1
• DZ = P V / (R T); Z = 0

According to the Arrhenius equation, how does the reaction rate constant (k) change as the activation energy (E_a) increases at constant temperature?

• Ak increases linearly.
• Bk decreases exponentially.
• Ck increases exponentially.
• Dk remains unchanged.

For a first-order liquid-phase reaction seeking 90% conversion, how does the required volume of a single Continuous Stirred-Tank Reactor (CSTR) compare to a single Plug Flow Reactor (PFR)?

• AThe CSTR volume is smaller than the PFR volume.
• BThe CSTR volume is equal to the PFR volume.
• CThe CSTR volume is significantly larger than the PFR volume.
• DThe PFR volume is infinitely large compared to the CSTR.

Under the Langmuir-Hinshelwood mechanism for a catalytic reaction A + B -> C, what is the key assumption regarding the reacting species?

• AOnly species A is adsorbed on the catalyst surface, while B reacts from the gas phase.
• BBoth species A and B must be adsorbed on adjacent active sites of the catalyst surface to…
• CThe reaction occurs entirely in the gas phase without adsorption.
• DProduct C must remain permanently adsorbed on the surface.

In industrial practice, why are multiple smaller CSTRs arranged in series preferred over a single large CSTR achieving the same conversion?

• AMultiple CSTRs in series behave closer to a plug flow reactor, reducing total volume.
• BSmaller reactors are always more expensive to operate.
• CA series of CSTRs decreases the overall conversion of the reaction.
• DIt prevents any bypass or short-circuiting of reactants.

For parallel reactions where reactant A decomposes to desired product D (order a1) and undesired product U (order a2), what design condition favors D if a1 > a2?

• AOperating at low concentration of reactant A.
• BOperating at high concentration of reactant A.
• CThe concentration of A has no effect on selectivity.
• DUsing a completely backmixed reactor (CSTR).

What physical situation is indicated by a high Thiele modulus (phi > 30) for a reaction occurring in a porous catalyst pellet?

• AThe reaction rate is limited by external mass transfer.
• BThe reaction rate is limited by surface reaction kinetics.
• CThe reaction rate is limited by internal pore diffusion.
• DThe catalyst pellet is fully utilized.

How is space velocity defined in chemical reactor design, and what are its dimensions?

• AThe ratio of feed volumetric flow rate to reactor volume; dimensions of time^(-1).
• BThe ratio of reactor volume to feed volumetric flow rate; dimensions of time.
• CThe velocity of reactants flowing through the reactor; dimensions of length/time.
• DThe mass flow rate divided by reactor cross-sectional area; dimensions of mass/(length^2…

How does the presence of an inert gas in a feed stream affect the adiabatic flame temperature of a combustion reaction?

• AIt increases the adiabatic flame temperature by increasing the heat of combustion.
• BIt decreases the adiabatic flame temperature by acting as a heat sink.
• CIt has no effect because the inert gas does not react.
• DIt increases the temperature by increasing the system pressure.

Which equation describes the relationship between the vapor pressure of a pure substance and its temperature, assuming a constant heat of vaporization?

• AThe Clausius-Clapeyron equation
• BThe Antoine equation
• CThe Van der Waals equation
• DThe Peng-Robinson equation

Under what set of assumptions does Bernoulli's equation apply along a streamline?

• AIncompressible, inviscid, steady, and frictionless flow.
• BCompressible, viscous, unsteady, and turbulent flow.
• CIncompressible, viscous, steady, and rotational flow.
• DCompressible, inviscid, steady, and non-isentropic flow.

For fluid flow in a circular pipe, what is the critical Reynolds number that typically separates laminar flow from transitional and turbulent flow?

• A2100
• B4000
• C10000
• D500

How is the relationship between the Darcy-Weisbach friction factor (f_D) and the Fanning friction factor (f_F) defined?

• Af_D = 4 * f_F
• Bf_F = 4 * f_D
• Cf_D = f_F
• Df_D = f_F / 4

What is the physical consequence if the Net Positive Suction Head Available (NPSHa) at a centrifugal pump inlet falls below the Net Positive Suction Head Required (NPSHr)?

• AThe pump motor will draw less electrical current.
• BCavitation will occur, causing mechanical damage and loss of head.
• CThe fluid velocity at the discharge will increase.
• DThe pump will automatically reverse its direction of rotation.

Why does an orifice plate flow meter result in a higher permanent pressure loss compared to a Venturi meter?

• AThe orifice plate has a larger discharge coefficient.
• BThe orifice plate lacks a gradual expansion cone, leading to large frictional losses in t…
• CThe orifice plate is made of high-friction materials.
• DFluid velocity decreases as it passes through the orifice plate.

Which non-Newtonian fluid behavior is characterized by a decrease in apparent viscosity under increasing shear rate?

• ADilatant (shear-thickening)
• BPseudoplastic (shear-thinning)
• CBingham plastic
• DNewtonian

According to boundary layer theory, how does the boundary layer thickness (delta) over a flat plate scale with the distance from the leading edge (x) in laminar flow?

• Adelta proportional to x
• Bdelta proportional to x^(1/2)
• Cdelta proportional to x^(2)
• Ddelta proportional to x^(-1/2)

What parameters determine the minimum fluidization velocity in a packed bed of solids?

• AThe balance between drag force exerted by the fluid and the buoyant weight of the particl…
• BThe superficial velocity of the fluid entering the bed only.
• CThe thermal conductivity of the solid particles.
• DThe length of the piping system feeding the fluid.

How is the thermal resistance (R) of a flat wall of thickness L, surface area A, and thermal conductivity k defined in heat conduction?

• AR = k A / L
• BR = L / (k A)
• CR = L k / A
• DR = A / (L k)

Why is a counter-current heat exchanger thermodynamically superior to a co-current (parallel) heat exchanger?

• AIt yields a larger Logarithmic Mean Temperature Difference (LMTD) for the same inlet and…
• BIt prevents the hot fluid from cooling below the cold fluid's outlet temperature.
• CIt requires a higher volumetric flow rate of cooling water.
• DIt minimizes the pressure drop across both fluid channels.

When sizing heat exchangers, when is the Effectiveness-NTU (Number of Transfer Units) method preferred over the Logarithmic Mean Temperature Difference (LMTD) method?

• AWhen only the inlet temperatures of both fluid streams are known.
• BWhen the heat exchanger operates under co-current flow only.
• CWhen the overall heat transfer coefficient (U) is unknown.
• DWhen phase change occurs in both streams.

According to the Stefan-Boltzmann law, how does the emissive power of a blackbody scale with its absolute temperature (T)?

• AIt scales with T.
• BIt scales with T^2.
• CIt scales with T^4.
• DIt scales with T^3.

Which dimensionless group represents the ratio of buoyancy forces to viscous forces in natural (free) convection?

• APrandtl number (Pr)
• BGrashof number (Gr)
• CNusselt number (Nu)
• DReynolds number (Re)

In pool boiling heat transfer, what physical phenomenon occurs at the critical heat flux (CHF) point?

• AThe boiling transition from nucleate boiling to film boiling starts, forming a vapor film…
• BThe liquid completely freezes on the heated surface.
• CThe heat transfer coefficient reaches its absolute minimum.
• DBubbles stop forming and heat transfer occurs purely by conduction.

What is the shaft power required by a water pump delivering 0.05 m^3/s of water against a total dynamic head of 30 m, assuming a pump efficiency of 75%? (Density of water = 1000 kg/m^3, g = 9.81 m/s^2)

• A14.7 kW
• B19.6 kW
• C11.0 kW
• D29.4 kW

Under what condition does choked flow occur in a converging-diverging nozzle carrying a compressible fluid?

• AWhen the velocity at the throat reaches the local speed of sound (Mach = 1).
• BWhen the pressure at the nozzle exit reaches vacuum.
• CWhen the fluid density becomes zero at the throat.
• DWhen the flow changes from turbulent to laminar.

What physical property ratio does the dimensionless Prandtl number (Pr) represent, and what does Pr = 1 imply?

• AMomentum diffusivity to thermal diffusivity; velocity and thermal boundary layers grow at…
• BThermal diffusivity to momentum diffusivity; the thermal boundary layer is much thicker.
• CConvective to conductive heat transfer; conduction dominates.
• DViscous forces to buoyancy forces; buoyancy dominates.

How does the deposition of a fouling layer on the surface of a heat exchanger tube affect the overall heat transfer coefficient (U)?

• AIt decreases U by adding conductive thermal resistance in series.
• BIt increases U by increasing the fluid turbulence near the wall.
• CIt has no effect on U because the tube thickness remains constant.
• DIt increases U by acting as a thermal conductor.

In two-phase gas-liquid flow through a pipe, what is the primary purpose of the Lockhart-Martinelli correlation?

• ATo calculate the two-phase frictional pressure drop based on single-phase pressure drops.
• BTo predict the transition from laminar to turbulent flow.
• CTo determine the sonic velocity of a gas-liquid mixture.
• DTo size the diameter of the pipeline.

Which equation is commonly used to estimate the Nusselt number for fully developed turbulent flow in smooth circular tubes?

• AThe Dittus-Boelter equation
• BThe Ergun equation
• CThe Fanning equation
• DThe Fenske equation

How is Fick's First Law of Diffusion represented mathematically for one-dimensional binary diffusion of species A in B?

• AJ_A = -D_AB * dC_A/dz
• BJ_A = D_AB * dC_A/dz
• CJ_A = -D_AB * d^2C_A/dz^2
• DJ_A = -C_A * dD_AB/dz

According to the two-film theory of mass transfer, how is the overall mass transfer resistance (1/K_y) related to individual film resistances (1/k_y and 1/k_x) for gas-phase absorption?

• A1/K_y = 1/k_y + m / k_x
• B1/K_y = 1/k_y + 1 / k_x
• C1/K_y = m / k_y + 1 / k_x
• D1/K_y = 1/k_y - m / k_x

In the McCabe-Thiele method for distillation column design, what does the operating line for the rectifying (enriching) section represent?

• AThe material balance between the vapor and liquid streams passing each other between stag…
• BThe equilibrium relationship between the liquid and vapor phases on each stage.
• CThe enthalpy balance of the feed stream.
• DThe minimum reflux ratio required to achieve separation.

How does the feed quality parameter (q) affect the slope of the feed line (q-line) in distillation column design, and what is its value for a saturated liquid feed?

• ASlope = q / (q - 1); q = 1
• BSlope = (q - 1) / q; q = 1
• CSlope = q / (q - 1); q = 0
• DSlope = -q / (q - 1); q = 1

In packed gas absorption columns, what is the consequence of operating the column above the flooding velocity?

• AThe gas flow rate becomes zero due to high liquid holdup.
• BThe liquid holdup increases rapidly, filling the column and causing high pressure drop an…
• CThe separation efficiency increases dramatically.
• DThe liquid flow rate through the bottom of the column increases.

On a ternary phase diagram for liquid-liquid extraction, what does the plait point represent?

• AThe point where the extract and raffinate phases become identical in composition, and the…
• BThe temperature at which three phases coexist at equilibrium.
• CThe composition of the feed stream entering the extraction column.
• DThe point where the solute concentration is zero in both phases.

What is the key assumption of the Langmuir adsorption isotherm compared to the Freundlich isotherm?

• AAdsorption is limited to a monolayer on a homogeneous surface with no interaction between…
• BAdsorption can occur in multiple layers on a heterogeneous surface.
• CThe rate of adsorption is independent of the solute concentration.
• DAdsorption only occurs at supercritical temperatures.

In reverse osmosis desalination, what is the phenomenon of concentration polarization, and what is its effect on membrane performance?

• AAccumulation of solute at the membrane surface, which increases osmotic pressure and redu…
• BThe alignment of water molecules under an electric field, which speeds up filtration.
• CThe degradation of the polymer membrane due to high chlorine content in the feed.
• DThe increase in membrane pore size due to high operating pressure.

During the drying of a wet solid, when does the transition from the constant-rate drying period to the falling-rate drying period occur?

• AAt the critical moisture content.
• BAt the equilibrium moisture content.
• CWhen the solid is completely dry.
• DWhen the air relative humidity reaches 100%.

In industrial crystallization, how does the cooling rate affect the crystal size distribution?

• ARapid cooling promotes high supersaturation, leading to rapid nucleation and smaller aver…
• BRapid cooling slows down nucleation, leading to larger, highly pure crystals.
• CCooling rate has no effect on crystal size; it only affects the yield.
• DSlow cooling prevents crystal growth, resulting in amorphous solids.

Why is extractive distillation preferred over conventional fractional distillation for separating azeotropic mixtures?

• AIt uses a non-volatile solvent that alters the relative volatility of the components with…
• BIt operates at lower pressures to bypass the azeotropic point.
• CIt reacts chemically with one of the components to remove it from the system.
• DIt uses steam to vaporize both components at lower temperatures.