Free PE Chemical exam Practice Questions

Sample Practice Questions

Try these 10 sample questions from the PE Chemical exam practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1A process engineer converts a solvent delivery of 2.5 m³ into a mass inventory. The solvent density at the delivery temperature is 800 kg/m³. What mass was delivered?

   1. A. 320 kg
   2. B. 2,000 kg
   3. C. 0.003125 kg
   4. D. 20,000 kg

   Answer: B

   Explanation: DOE states, "Density is the measure of the mass per unit volume of a material (density = mass/volume)." Thus mass = 800 × 2.5 = 2,000 kg; density is multiplied by volume, not divided by it. Dividing density by volume gives 320; dividing volume by density gives 0.003125; a tenfold conversion error gives 20,000.

   Reference: DOE Fundamentals Handbook: Chemistry, Volume 1 — Module 1, Chemical Equations, Density, p. 37

2. 2An engineer models a sealed rigid nitrogen vessel as an ideal gas. Its absolute temperature rises from 300 K to 450 K while its initial absolute pressure is 200 kPa. What is the final absolute pressure?

   1. A. 133 kPa
   2. B. 100 kPa
   3. C. 300 kPa
   4. D. 350 kPa

   Answer: C

   Explanation: DOE states, "the pressure of a gas varies directly with temperature when the volume is held constant". Therefore P₂ = 200(450/300) = 300 kPa. Both pressure and temperature must be absolute.

   Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 1 — Module 1, Compression Processes, p. 97, Equation 1-41

3. 3An insulated wall has area 2 m², thickness 0.10 m, thermal conductivity 0.05 W/(m·K), and a 40 K temperature difference across the insulation. For steady one-dimensional conduction, what is the heat-transfer rate?

   1. A. 0.4 W
   2. B. 4 W
   3. C. 40 W
   4. D. 400 W

   Answer: C

   Explanation: DOE states, "Heat transfer by conduction is dependent upon the driving "force" of temperature difference and the resistance to heat transfer." Equation 2-4 gives Q̇ = kAΔT/Δx = 0.05 × 2 × 40/0.10 = 40 W. A multiplies by thickness, B omits thickness, and D introduces a tenfold length error.

   Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 2 — Module 2, Conduction Heat Transfer, pp. 6–7, Equation 2-4

4. 4In an isothermal kinetic experiment, doubling concentration of B increases reaction rate by a factor of four while other concentrations remain fixed. For a power-law rate model, what is the partial order in B?

   1. A. 0
   2. B. 1
   3. C. 2
   4. D. 4

   Answer: C

   Explanation: IUPAC defines partial reaction orders through the concentration exponents in the rate law. It states, "The order of reaction is only defined if the particular rate law applies." Here 2ᵐ = 4, so m = 2.

   Reference: Quantities, Units and Symbols in Physical Chemistry (IUPAC Green Book) — Printed page 63, Chemical Kinetics and Photochemistry, reaction-order definition and note (5)

5. 5A pressure tap is 5 m below the free surface of an open tank of liquid with density 800 kg/m³. Using g = 9.81 m/s², what gauge pressure is due to the liquid column?

   1. A. 1.57 kPa
   2. B. 4.00 kPa
   3. C. 39.2 kPa
   4. D. 392 kPa

   Answer: C

   Explanation: DOE states that liquid-column pressure is proportional to "the height of the column and the density of the water." Applying P = ρgh gives 800 × 9.81 × 5 = 39,240 Pa = 39.2 kPa.

   Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 3 — Module 3, Continuity Equation, Summary, p. 16

6. 6Across a stationary dilute liquid film, concentration decreases by 20 mol/m³ over 0.001 m in the positive coordinate direction. With D = 1 × 10⁻⁹ m²/s, what is the steady diffusive molar flux magnitude?

   1. A. 2 × 10^(-11) mol/(m^2 s)
   2. B. 2 × 10^(-8) mol/(m^2 s)
   3. C. 2 × 10^(-5) mol/(m^2 s)
   4. D. 2 × 10^(4) mol/(m^2 s)

   Answer: C

   Explanation: IUPAC defines "D = −Jn /(dc/dl)". Hence |Jn| = D|dc/dl| = 10⁻⁹ × 20/0.001 = 2 × 10⁻⁵ mol/(m²·s).

   Reference: Quantities, Units and Symbols in Physical Chemistry (IUPAC Green Book) — Section 2.15, p. 81, diffusion coefficient and note 4

7. 7An engineer schedules revalidation of the process hazard analysis for a process subject to federal OSHA PSM requirements. What is the longest routine interval permitted after completion of the initial analysis?

   1. A. One year
   2. B. Three years
   3. C. Five years
   4. D. Ten years

   Answer: C

   Explanation: OSHA requires updating and revalidation "At least every five (5) years after the completion of the initial process hazard analysis". The maximum routine interval is five years.

   Reference: Process safety management of highly hazardous chemicals (29 CFR 1910.119) — 29 CFR 1910.119(e)(6)

8. 8For a batch preparation, 12 mol of solute is dissolved and the final solution volume is adjusted to 30 L. What concentration should the engineer enter in the batch record?

   1. A. 0.40 mol/L
   2. B. 2.5 mol/L
   3. C. 4.0 mol/L
   4. D. 360 mol/L

   Answer: A

   Explanation: DOE states, "Molarity is defined as moles of solute per liter of solution." The final solution volume controls: 12/30 = 0.40 mol/L.

   Reference: DOE Fundamentals Handbook: Chemistry, Volume 1 — Module 1, Chemical Equations, Molarity, p. 37

9. 9A sealed process vessel exchanges heat through its jacket and work through its agitator shaft, but no material enters or leaves. Which thermodynamic system classification applies?

   1. A. A closed system
   2. B. An isolated system
   3. C. An open system
   4. D. An adiabatic system

   Answer: A

   Explanation: DOE states, "A closed system has no transfer of mass with its surroundings, but may have a transfer of energy (either heat or work) with its surroundings." Heat and shaft work do not make this vessel an open system. An adiabatic boundary excludes the stated jacket heat exchange.

   Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 1 — Module 1, Thermodynamic Systems and Processes, Types of Thermodynamic Systems, p. 27

10. 10A hot process surface of 4 m² is at 100°C while the surrounding fluid bulk temperature is 40°C. With h = 25 W/(m²·K), what convection heat loss is predicted?

    1. A. 1.5 kW
    2. B. 4.0 kW
    3. C. 6.0 kW
    4. D. 10.0 kW

    Answer: C

    Explanation: DOE gives the convection relation with the product "h A ∆T" in Equation 2-9. Thus 25 × 4 × (100 − 40) = 6,000 W = 6.0 kW. The alternatives omit area, use the bulk fluid temperature rather than its difference from the surface, or use surface temperature without subtracting bulk temperature.

    Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 2 — Module 2, Convection Heat Transfer, p. 19, Equation 2-9