Chemical Engineering Mock Interview Questions & Practice

What is the Second Law of Thermodynamics, and why is it important in evaluating chemical process feasibility?

Key points to cover:

• Entropy of an isolated system never decreases
• Heat doesn't spontaneously flow from cold to hot
• Determines maximum theoretical efficiency and constrains spontaneous processes

What is relative volatility, and what does it indicate about the ease of separating two components by distillation?

Key points to cover:

• The ratio of the vapor-liquid equilibrium ratios (K-values) of two components
• Higher relative volatility indicates easier separation by distillation
• A value close to 1 indicates the components are difficult to separate

How does temperature affect the equilibrium constant of a reaction, and what determines the direction of the effect?

Key points to cover:

• Depends on whether the reaction is exothermic or endothermic
• Exothermic: increasing temperature shifts equilibrium toward reactants
• Endothermic: increasing temperature shifts equilibrium toward products

What is the log mean temperature difference (LMTD), and why is it used in heat exchanger design?

Key points to cover:

• A logarithmic average of hot/cold stream temperature differences
• At each end of a heat exchanger
• Used because the driving temperature difference varies non-linearly along the exchanger

What is the mass transfer coefficient, and what role does it play in interphase mass transfer calculations?

Key points to cover:

• Quantifies the rate of mass transfer per unit area per unit driving force
• At a phase boundary
• Analogous to the heat transfer coefficient in convective heat transfer

What is a theoretical (equilibrium) stage in a separation process, and what does it represent?

Key points to cover:

• An idealized contact stage
• Where the two phases leaving are assumed to be in complete equilibrium
• Used as a conceptual/calculation unit for multi-stage separation equipment

What is the Arrhenius equation, and what does it describe about reaction rate?

Key points to cover:

• Describes the temperature dependence of a reaction's rate constant
• Relates it to an activation energy and a pre-exponential factor
• Rate generally increases exponentially with increasing temperature

What is residence time, and why is it a critical parameter in reactor design?

Key points to cover:

• The average amount of time reactant material spends within a reactor
• Directly determines the extent of reaction/conversion achievable
• Given the reaction's rate

What is residence time distribution (RTD), and what does it characterize about a real reactor?

Key points to cover:

• A statistical distribution describing how long fluid elements spend
• Within a reactor
• Characterizes the extent of non-ideal flow/mixing behavior

What is feedback control, and how does it operate in a typical process control loop?

Key points to cover:

• Measures the actual controlled variable
• Compares it to the setpoint to compute an error
• Adjusts the manipulated variable based on that error

What is the difference between accuracy and precision in the context of a measuring instrument?

Key points to cover:

• Accuracy: how close a measurement is to the true value
• Precision: how repeatable/consistent measurements are with each other
• Regardless of whether they are close to the true value

What is Hazard and Operability (HAZOP) analysis, and what is its purpose in process design?

Key points to cover:

• A structured technique for identifying potential hazards
• By examining deviations from normal operating conditions
• Proactively identifies and mitigates risks before a plant is built

What is hydrostatic pressure, and how does it vary with depth in a fluid?

Key points to cover:

• Pressure exerted by a fluid at rest due to the weight of fluid above
• Increases linearly with depth
• Proportional to fluid density, gravitational acceleration, and depth

What is the Reynolds number, and what does it indicate about a flow?

Key points to cover:

• A dimensionless ratio of inertial forces to viscous forces
• Used to predict whether a flow will be laminar or turbulent
• With a critical value marking the transition

What is cavitation in a centrifugal pump, and what conditions promote it?

Key points to cover:

• Local pressure inside the pump drops below the fluid's vapor pressure
• Vapor bubbles form and then collapse violently
• Promoted by insufficient suction head or excessive pump speed