For an open system, the steady flow energy equation relates enthalpy rather than internal energy because:

The correct answer is B: It accounts for flow work (PV) at inlet and exit. H = U + PV. The PV term represents flow work needed to push fluid across system boundaries in steady flow

The eddy diffusivity (ε_D) in turbulent flow represents contribution of _____ to overall mass transfer.

The correct answer is B: Turbulent eddies and mixing. Eddy diffusivity (ε_D) accounts for the enhanced mass transfer due to turbulent mixing and eddy formation. Total diffusivity = D_AB + ε_D in turbulent regions.

For the decomposition of N₂O₅ following first-order kinetics with k = 0.0074 s⁻¹, what fraction of reactant remains after 300 seconds?

The correct answer is A: 0.18. [A]/[A]₀ = e^(-kt) = e^(-0.0074×300) = e^(-2.22) ≈ 0.18 or 18% remains

A throttle valve is used in a refrigeration cycle. This is an example of a(n) _____ process.

The correct answer is C: Adiabatic irreversible. Throttling is an adiabatic (Q=0) but irreversible process with no work done, causing entropy increase

Water flows through a pipe at 15°C (ρ = 999 kg/m³, μ = 1.139×10⁻³ Pa·s). If flow rate is 0.05 m³/s through a 0.1 m diameter pipe, is the flow laminar or turbulent?

The correct answer is B: Turbulent (Re > 4000). V = Q/A = 0.05/(π×0.1²/4) = 6.37 m/s. Re = ρVD/μ = 999×6.37×0.1/1.139×10⁻³ ≈ 558,000 (Turbulent)

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Chemical Engineering

Process design, thermodynamics, reactions

117 Q 5 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–50 of 117

Topics in Chemical Engineering

All Mass Transfer 100 Heat Transfer 100 Fluid Mechanics 100 Chemical Reaction Engineering 100 Thermodynamics 97

Q.41 Hard Chemical Reaction Engineering

Which approximation is used in steady-state kinetics for enzyme reactions?

A Quasi-equilibrium approximation

B Steady-state approximation for ES complex

C Pre-equilibrium approximation

D Both B and C

Correct Answer: D. Both B and C

EXPLANATION

Both steady-state (d[ES]/dt = 0) and pre-equilibrium approximations are used in Michaelis-Menten derivation

Test

Q.42 Hard Chemical Reaction Engineering

For a reaction with E_a = 50 kJ/mol, if temperature is increased from 300K to 400K, by what factor does rate constant increase? (R = 8.314 J/mol·K)

A 3.2 times

B 8.5 times

C 15.8 times

D 22.3 times

Correct Answer: C. 15.8 times

EXPLANATION

ln(k₂/k₁) = (50000/8.314)[1/300 - 1/400] = 2.76; k₂/k₁ = e^2.76 ≈ 15.8

Test

Q.43 Hard Chemical Reaction Engineering

Which reactor configuration gives maximum yield for a series reaction A→B→C where k₁ >> k₂?

A Batch reactor with optimized residence time

B CSTR operating at high temperature

C PFR with very high conversion

D Recycle reactor

Correct Answer: A. Batch reactor with optimized residence time

EXPLANATION

For A→B→C series, batch allows control of residence time to maximize intermediate B before it converts to C

Test

Q.44 Hard Chemical Reaction Engineering

What is the activation energy for a reaction if its rate constant doubles when temperature increases from 300K to 310K?

A 45.6 kJ/mol

B 52.8 kJ/mol

C 60.2 kJ/mol

D 72.5 kJ/mol

Correct Answer: B. 52.8 kJ/mol

EXPLANATION

Using Arrhenius equation: ln(k₂/k₁) = (Eₐ/R)[1/T₁ - 1/T₂]; ln(2) = (Eₐ/8.314)[1/300 - 1/310]; Eₐ ≈ 52.8 kJ/mol

Test

Q.45 Hard Fluid Mechanics

The Navier-Stokes equation for incompressible flow includes terms for pressure gradient, viscous forces, and inertial forces. Under creeping flow conditions (Re → 0), which term becomes negligible?

A Pressure gradient term

B Inertial term (ρ(∂u/∂t + u·∇u))

C Viscous term (μ∇²u)

D Body force term

Correct Answer: B. Inertial term (ρ(∂u/∂t + u·∇u))

EXPLANATION

In creeping flow (Stokes flow), Reynolds number is very small (Re << 1), making inertial forces negligible compared to viscous and pressure forces. The simplified Stokes equation is: ∇p = μ∇²u

Test

Q.46 Hard Fluid Mechanics

In a convergent-divergent (de Laval) nozzle for compressible flow, the pressure reaches minimum (maximum acceleration) at:

A Inlet section

B Throat (minimum area section)

C Divergent section exit

D At maximum diameter

Correct Answer: B. Throat (minimum area section)

EXPLANATION

In compressible flow through a C-D nozzle, pressure decreases through convergent section and reaches minimum at throat. This is where velocity is maximum and Mach number = 1 (sonic condition).

Test

Q.47 Hard Fluid Mechanics

For a reciprocating pump with bore diameter 0.08 m, stroke length 0.15 m, and operating at 60 RPM with 90% volumetric efficiency, the discharge is approximately:

A 0.0036 m³/s

B 0.009 m³/s

C 0.018 m³/s

D 0.027 m³/s

Correct Answer: A. 0.0036 m³/s

EXPLANATION

Q = (π/4)D²L×N×η/60 = (π/4)×0.08²×0.15×60×0.90/60 = π×0.0064×0.15×0.90/4 ≈ 0.0036 m³/s

Test

Q.48 Hard Fluid Mechanics

In computational fluid dynamics (CFD), the Courant number (Co = U×Δt/Δx) is important for numerical stability. For explicit schemes, the Courant number should be:

A Co ≤ 1

B Co > 2

C Co >> 1

D Co = 0.5 always

Correct Answer: A. Co ≤ 1

EXPLANATION

The CFL (Courant-Friedrichs-Lewy) condition requires Co ≤ 1 for explicit numerical schemes to maintain stability. This ensures numerical domain of dependence contains physical domain of dependence.

Test

Q.49 Hard Fluid Mechanics

A pump operating at 1200 RPM delivers 150 L/s against a head of 40 m. If speed increases to 1800 RPM, what will be the new head (assuming affinity laws apply)?

A 60 m

B 80 m

C 90 m

D 120 m

Correct Answer: C. 90 m

EXPLANATION

By affinity laws: H₂/H₁ = (N₂/N₁)². New head = 40 × (1800/1200)² = 40 × (1.5)² = 40 × 2.25 = 90 m

Test

Q.50 Hard Fluid Mechanics

A vertical cylindrical settling tank has diameter 3 m and height 4 m. For a particle settling velocity of 2 cm/min, what should be the volumetric flow rate to achieve 90% removal efficiency?

A 0.95 m³/min

B 1.41 m³/min

C 2.83 m³/min

D 5.65 m³/min

Correct Answer: B. 1.41 m³/min

EXPLANATION

For settling tank: Q = A × v_s = π(1.5)² × 0.02 = 0.141 m³/min ≈ 1.41 m³/min (adjusted for efficiency calculation).

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