DC CHEMICAL ENGINEER LICENSURE EXAM PRACTICE QUESTIONS AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2026 Q&A |

DC CHEMICAL ENGINEER LICENSURE EXAM PRACTICE QUESTIONS AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALE 2026 Q&A | 1. In a gas absorption process involving a dilute solute in air being absorbed into a liquid solvent, which of the following best describes the primary driving force for mass transfer across the gas-liquid interface? A. Difference in total pressure between phases B. Difference in chemical potential of the solute between phases C. Difference in temperature between gas and liquid phases D. Difference in liquid viscosity across the interface Answer: B Mass transfer in absorption is fundamentally driven by a gradient in chemical potential, which is often expressed in terms of concentration or partial pressure differences between phases. The solute moves from a region of higher chemical potential (gas phase) to lower chemical potential (liquid phase) until equilibrium is reached. ________________________________________ 2. A perfectly mixed continuous stirred-tank reactor (CSTR) operating at steady state for a first-order irreversible reaction will exhibit which characteristic relationship between conversion and residence time? A. Conversion is independent of residence time B. Conversion increases linearly with residence time C. Conversion approaches an asymptotic maximum as residence time increases D. Conversion decreases exponentially with residence time Answer: C For a first-order reaction in a CSTR, conversion increases with residence time but approaches a limiting value due to the balance between reaction rate and continuous inflow/outflow, resulting in an asymptotic behavior rather than linear growth. Conversion is given by X = (kτ)/(1 + kτ). ________________________________________ 3. Which thermodynamic condition is required for phase equilibrium between liquid and vapor phases of a multicomponent system? A. Equal enthalpy in both phases for each component B. Equal fugacity of each component in both phases C. Equal temperature gradients across phases D. Equal heat capacities in both phases Answer: B Phase equilibrium is achieved when the fugacity (effective escaping tendency) of each component is equal in all phases present, ensuring no net mass transfer between phases at equilibrium. ________________________________________ 4. In shell-and-tube heat exchangers, the use of baffles primarily serves to: A. Increase fluid viscosity and reduce turbulence B. Enhance heat transfer by increasing shell-side turbulence C. Reduce thermal conductivity of tube walls D. Prevent phase change within the tubes Answer: B Baffles force the shell-side fluid to change direction, increasing turbulence and improving the overall heat transfer coefficient by reducing boundary layer thickness. ________________________________________ 5. The primary purpose of dimensional analysis in chemical engineering is to: A. Determine reaction mechanisms experimentally B. Convert empirical equations into thermodynamic models C. Reduce the number of variables and ensure equation consistency D. Increase numerical precision of simulation results Answer: C Dimensional analysis ensures that equations are dimensionally consistent and reduces the complexity of physical problems by grouping variables into dimensionless parameters such as Reynolds or Sherwood numbers. ________________________________________ 6. In distillation, relative volatility is defined as the: A. Ratio of liquid densities of two components B. Ratio of vapor pressures of two components C. Ratio of equilibrium constants of two components D. Ratio of heat capacities of two components Answer: C Relative volatility is the ratio of equilibrium constants (or K-values) of components and indicates how easily one component can be separated from another by distillation. ________________________________________ 7. Which law governs the proportional relationship between gas solubility in a liquid and its partial pressure above the liquid at low concentrations? A. Raoult's Law B. Dalton's Law C. Henry's Law D. Fick's Law Answer: C Henry's Law states that the concentration of a dissolved gas is directly proportional to its partial pressure above the liquid, provided the system is dilute and at equilibrium. ________________________________________ 8. In fluid flow through a packed bed, the pressure drop is most commonly predicted using which model? A. Bernoulli equation B. Hagen-Poiseuille equation C. Ergun equation D. Fourier's law Answer: C The Ergun equation accounts for both viscous and inertial contributions to pressure drop in packed beds, making it suitable for porous media flow analysis. ________________________________________ 9. A catalyst primarily functions in a chemical reaction by: A. Increasing reaction equilibrium constant B. Increasing activation energy C. Providing an alternative reaction pathway with lower activation energy D. Shifting equilibrium toward products Answer: C Catalysts accelerate reaction rates by lowering the activation energy required for reaction without altering the equilibrium position or thermodynamic properties. ________________________________________ 10. The Reynolds number in fluid mechanics represents the ratio of: A. Viscous forces to gravitational forces B. Inertial forces to viscous forces C. Pressure forces to surface tension forces D. Thermal forces to momentum forces Answer: B The Reynolds number is the ratio of inertial forces to viscous forces and is used to predict flow regimes (laminar, transitional, or turbulent). ________________________________________ 11. A system undergoes a cyclic process. What is the net change in internal energy of the system? A. Positive B. Zero C. Negative D. Depends on the path taken Answer: B Internal energy is a state function. For any cyclic process, the initial and