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.
For parallel reactions A→B and A→C, the selectivity of B over C is defined as:
Answer: A
Selectivity = rate of desired product formation/rate of undesired product formation
Q.303Easy
Which statement is correct about the residence time distribution (RTD) in an ideal plug flow reactor?
Answer: B
In ideal PFR, E(t) = δ(t-τ), meaning all molecules have identical residence time equal to τ
Q.304Medium
In a catalytic reaction, which parameter does NOT affect the rate of reaction?
Answer: C
Catalyst doesn't change ΔG or equilibrium position; it only lowers Eₐ. ΔG determines feasibility, not rate
Q.305Medium
For the reaction 2A → B, if initial concentration of A is 2 mol/L and concentration after 5 minutes is 1 mol/L, calculate rate constant (assuming second-order):
Answer: A
For 2nd order: 1/[A] = 1/[A]₀ + kt; 11 = 21 + k(5); k = 0.1 L/(mol·min)
Q.306Easy
What is the order of reaction if the rate law is: rate = k[A]^(21)[B]?
Answer: B
Order = sum of exponents = 21 + 1 = 1.5 (fractional order, common in enzyme kinetics)
Q.307Easy
In an isothermal CSTR, if feed concentration C_A0 = 10 mol/m³ and outlet concentration C_A = 2 mol/m³, conversion is:
In enzyme catalysis, what does the Michaelis-Menten constant (K_m) represent?
Answer: A
K_m represents substrate concentration [S] at which reaction velocity = V_max/2
Q.312Medium
For an exothermic reaction in an adiabatic reactor, what happens to the reaction rate as conversion increases?
Answer: C
Adiabatic reactor: no heat removal; exothermic reaction raises temperature, increasing k and hence rate
Q.313Hard
Which approximation is used in steady-state kinetics for enzyme reactions?
Answer: D
Both steady-state (d[ES]/dt = 0) and pre-equilibrium approximations are used in Michaelis-Menten derivation
Q.314Medium
For autocatalytic reactions, which reactor gives highest conversion at equilibrium?
Answer: D
Equilibrium conversion is thermodynamically determined and independent of reactor type
Q.315Easy
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.316Hard
For consecutive reactions A→B→C, the concentration of intermediate B is maximum at time t_max. This time depends on:
Answer: A
t_max = ln(k₂/k₁)/(k₂-k₁), depends only on rate constants, independent of [A]₀
Q.317Easy
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.319Easy
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.320Medium
For a second-order reaction A+B→C with equal initial concentrations of 1 mol/L, if the rate constant is 0.5 L/(mol·min), what is the time required for 50% conversion?
Answer: A
For second-order reaction with CA0 = CB0: 1/CA - 1/CA0 = kt. At 50% conversion, CA = 0.5. So (01.5 - 11) = 0.5×t gives t = 2 minutes
