Chemical Engineering questions for GATE and PSU exams are built on a handful of core subjects applied in many ways. Practice spans fluid mechanics, heat transfer, mass transfer, chemical reaction engineering, thermodynamics, process control and instrumentation, and plant design economics. Numerical solutions carry the assumptions written out, because the assumption is usually what separates a correct answer from a plausible one.
In a fluidized bed reactor (FBR), particles exhibit properties of both solids and fluids. What is this phenomenon called?
Answer: B
Fluidization: particles suspended in gas/liquid flow with properties intermediate between fixed bed and fluid
Q.87Easy
In a batch reactor operating at constant volume, the rate of reaction for a first-order reaction A→B is -rA = kCA. If the initial concentration is 2 mol/L and k = 0.1 min⁻¹, what will be the concentration after 10 minutes?
What is the primary advantage of a plug flow reactor (PFR) over a continuous stirred-tank reactor (CSTR) for reactions with high activation energy?
Answer: C
PFR provides higher conversion than CSTR for the same volume because of better concentration gradient utilization and no back-mixing of unreacted material
Q.89Easy
In the context of reaction kinetics, which statement best describes the rate-determining step (RDS) in a multi-step reaction mechanism?
Answer: B
The rate-determining step is the slowest elementary step in the reaction mechanism, which governs the overall rate of the reaction regardless of its position in the sequence
Q.90Easy
What does the selectivity parameter in a competing reaction system measure?
Answer: B
Selectivity S = rate of desired product formation / rate of undesired product formation, used to optimize reactor conditions for maximum desired product yield
Q.91Easy
In a batch reactor operating at constant temperature, the reaction A → B follows second-order kinetics with rate constant k = 0.05 L/(mol·min). If initial concentration of A is 2 M, what is the time required to reduce the concentration to 0.5 M?
Answer: A
For second-order reaction: 1/[A]t - 1/[A]0 = kt. Therefore, 01.5 - 21 = 0.05×t gives 2 - 0.5 = 0.05t, so t = 30 minutes.
Q.92Easy
For a reversible reaction A ⇌ B with forward rate constant k_f = 0.3 s⁻¹ and reverse rate constant k_r = 0.1 s⁻¹, what is the equilibrium constant K_c?
Answer: B
At equilibrium, K_c = k_f/k_r = 0.03.1 = 3.0. This represents the ratio of forward to reverse rate constants at equilibrium.
Q.93Easy
For the decomposition of N₂O₅ following first-order kinetics with k = 0.0074 s⁻¹, what fraction of reactant remains after 300 seconds?
Which of the following statements about residence time distribution (RTD) is correct?
Answer: B
RTD characterizes how long different fluid elements spend in a reactor and is fundamental to reactor design, independent of whether flow is laminar or turbulent.
Q.95Easy
The Damköhler number (Da) for a chemical reaction is defined as the ratio of:
Answer: B
Da = (residence time)/(characteristic reaction time) = kτC^(n-1). When Da >> 1, reaction is fast; Da << 1, reaction is slow.
Q.96Easy
The conversion in a batch reactor at any time can be found by integrating the rate equation. For a first-order reaction, the half-life is:
Answer: D
For first-order: t₁/₂ = ln(2)/k = 0.693/k, which is independent of C₀ and inversely proportional to k.
Q.97Easy
For the reaction 2A + B → Products, if the reaction is 2nd order in A and 1st order in B, the rate equation is:
Answer: A
Reaction order is determined by experimental data, not stoichiometry. The given orders are 2nd in A and 1st in B, so rate law is r = k[A]²[B].
Q.98Easy
What is the order of reaction if the half-life period is independent of initial concentration?
Answer: B
For first-order reactions, t₁/₂ = 0.693/k, which is independent of initial concentration C₀.
Q.99Easy
For the reaction A + B → C, the rate law is r = kC_A²C_B. What is the overall order of reaction?
Answer: C
Overall order = sum of individual orders = 2 + 1 = 3.
Q.100Easy
For a reversible reaction at equilibrium, which statement is true?
Answer: B
At equilibrium, the net rate is zero because forward and reverse reaction rates are equal.
