21 + Interview Questions in Elements Of Reaction Kinetics in Chemical Reaction Engineering Page 1 InterviewSolution

1.	The rate determining step of a series of reactions is the one ____(a) That is fastest(b) That is slowest(c) That does not contribute to the reaction(d) That does not occurThis question was posed to me by my school teacher while I was bunking the class.My query is from Reducing the Size of Kinetic Models in portion Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Right option is (b) That is SLOWEST To elaborate: Rate DETERMINING step is the slowest of all the reaction steps. The rate determining step is important in DERIVING the rate EQUATION of a CHEMICAL reaction.

Discussion

2.	The unit of activation energy is ____(a) mol(b) mol.K(c) K(d) J/ molThis question was posed to me in quiz.The query is from Reaction Kinetics Elements topic in chapter Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» RIGHT choice is (d) J/ mol Easiest explanation: Activation ENERGY is expressed in J/ mol or KJ/ mol. Activation energy is the energy required for a CHEMICAL reaction to occur.

Discussion

3.	State true or false.Decomposition of nitrogen pentoxide follows second order mechanism, assuming that the kinetics is controlled by a single step mechanism.(a) Decomposition of nitrogen pentoxide follows second order mechanism, assuming that the kinetics is controlled by a single step mechanism.(b) True(c) FalseThis question was addressed to me in an online interview.Query is from Reducing the Size of Kinetic Models in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct option is (B) True The explanation: The rate of N2O5 DECOMPOSITION is given by, r = K[N2O5]. Hence, the reaction follows FIRST order.

Discussion

4.	State true or false.The value of frequency factor affects the temperature sensitivity of reaction.(a) The value of frequency factor affects the temperature sensitivity of reaction.(b) True(c) FalseI got this question in my homework.The question is from Reaction Kinetics Elements topic in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct answer is (b) True For explanation I would say: Frequency factor in ARRHENIUS equation does not affect the temperature sensitivity of the REACTION. Frequency factor is independent of temperature. It takes the units of RATE CONSTANT.

Discussion

5.	For a reaction with negative order n, which one of the following is true about reaction rate constant?(a) k = (-rA)(b) k = 1(c) k = \(\frac{-r_A}{C_A^n} \)(d) k =(-rA) × CA^nI have been asked this question during an interview.The origin of the question is Reaction Kinetics Elements in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct ANSWER is (d) k =(-RA) × CA^n Best EXPLANATION: For n<0, (-rA) = kCA^n Hence, k = (-rA) × CA^n

Discussion

6.	The order of the reaction involving the conversion of ozone to oxygen is ____(a) Zero order(b) First order(c) Second order(d) Third orderI got this question by my college professor while I was bunking the class.My doubt is from Reducing the Size of Kinetic Models in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Correct answer is (B) First order To EXPLAIN: The rate of decomposition of ozone is: -rO3= k[O3]^2[O2]^-1 Order = 2-1 = 1

Discussion

7.	At very low concentrations of azomethane, its decomposition follows which order?(a) First order(b) Zero order(c) Third order(d) Second orderThis question was posed to me by my school principal while I was bunking the class.The origin of the question is Reducing the Size of Kinetic Models topic in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct answer is (d) Second order Explanation: The RATE expression for decomposition of AZOMETHANE is: rN2 = \(\frac{k_1 k_3 C_{Azo}^2}{k_3+k_2 C_{Azo}} \) Where, K1, k2 and k3 are rate CONSTANTS of the 3 intermediate reactions involved in azomethane formation. At low concentration, k2 CAzo << k3 Hence, rN2=k1CAzo^2.

Discussion

8.	If rate of a zero order reaction is 10 \(\frac{mol}{m^3×s}\) and reaction time is 5s, then the value of rate constant is ____(a) 1 s^-1(b) 2 s^-1(c) 5 s^-1(d) 10 s^-1The question was asked in my homework.Question is taken from Reaction Kinetics Elements in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Correct option is (B) 2 s^-1 To explain I would SAY: (-RA) = kCA^n 10 = K (5) HENCE, k = 2 s^-1.

Discussion

9.	In the formation of phosgene from carbon monoxide and chlorine, which of the following is rate determining?(a) Decomposition of chlorine(b) Formation of COCl.(c) Reaction of COCl. with Cl2(d) Decomposition of CO2The question was posed to me by my school teacher while I was bunking the class.I'm obligated to ask this question of Reducing the Size of Kinetic Models topic in chapter Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The CORRECT option is (c) Reaction of COCl. with Cl2 Easy explanation: Reaction of COCl. with Cl2 is the SLOW reaction. Hence, it is the RATE determining STEP.

Discussion

10.	The reaction rate constant is related to reaction rate as ____(a) k α (-rA)(b) k α \(\frac{1}{(-r_A)} \)(c) k α e^(-rA)(d) k is independent of (-rA)I got this question in an interview for internship.My doubt stems from Reaction Kinetics Elements in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Right answer is (a) k α (-rA) To explain I WOULD SAY: The rate of reaction, (-rA) = kCA^N Where, n is the reaction order. The rate INCREASES as the VALUE of k increases.

Discussion

11.	An assumption of Steady State Approximation is ____(a) Reaction occurs without the formation of intermediates(b) Catalyst does not accelerate reaction rate(c) One of the intermediates in the reaction is consumed as quickly as it is generated(d) Equilibrium state is attained at the end of a reactionThe question was asked in an internship interview.This intriguing question originated from Reducing the Size of Kinetic Models in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct option is (c) One of the INTERMEDIATES in the REACTION is consumed as quickly as it is generated Explanation: The steady-state approximation is a method used to derive the rate expression. It is based on the ASSUMPTION that one INTERMEDIATE in the reaction mechanism is consumed as fast as it is generated.

Discussion

12.	The rate constant is a ____(a) Linear function of frequency factor(b) Exponential function of frequency factor(c) Logarithmic function of frequency factor(d) Sinusoidal function of frequency factorThe question was posed to me in an interview for internship.The origin of the question is Reaction Kinetics Elements in portion Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Right choice is (a) Linear FUNCTION of frequency factor For EXPLANATION: By ARRHENIUS equation, k = \(Ae^{\frac{-E_a}{RT}}\) K varies directly with respect to the frequency factor, A.

Discussion

13.	Formation of hydrogen iodide from the corresponding elements is a ____(a) Single step mechanism(b) Two step mechanism(c) Three step mechanism(d) Four step mechanismThis question was posed to me in an interview for job.Asked question is from Reducing the Size of Kinetic Models topic in chapter Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct option is (B) TWO step mechanism Easiest EXPLANATION: In the SLOW step, iodine decomposes to give 2[I]. In the consequent step, hydrogen REACTS with 2[I] to give hydrogen iodide.

Discussion

14.	Which among the following is true for liquid phase reactions of order n?(a) ln(\(\frac{-dC}{dt}\)) = lnk + n(lnC)(b) ln(\(\frac{-dC}{dt}\)) = lnk + lnC(c) ln(\(\frac{-dC}{dt}\)) = nlnk + lnC(d) ln(\(\frac{-dC}{dt}\)) = lnk + \(\frac{lnC}{n} \)I got this question by my college director while I was bunking the class.I want to ask this question from Reaction Kinetics Elements topic in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Right answer is (a) LN(\(\FRAC{-dC}{DT}\)) = lnk + n(LNC) To elaborate: (\(\frac{-dC}{dt}\)) = kC^n Taking natural logarithm on both sides, ln(\(\frac{-dC}{dt}\)) = lnk + n(lnC)

Discussion

15.	The reaction involving oxidation of nitric oxide to nitrous oxide follows the mechanism ____(a) \(\frac{-dO_2}{dt}\) = k[NO2]^2[O2](b) \(\frac{-dO_2}{dt}\) = k[NO2][O2](c) \(\frac{-dO_2}{dt}\) = k[NO2]^2[O2]^2(d) \(\frac{-dO_2}{dt}\) = k[NO2][O2]^2This question was posed to me in final exam.This interesting question is from Reducing the Size of Kinetic Models topic in portion Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The CORRECT OPTION is (a) \(\frac{-dO_2}{dt}\) = k[NO2]^2[O2] Explanation: In the FIRST STEP, 2 molecules of NO form N2O2. Further oxidation of N2O2 is the slowest step and it is the RATE determining step.

Discussion

16.	The rate constant and half life for reactions are related as ____(a) k α t0.5(b) k α \(\frac{1}{(t_{0.5})} \)(c) k α e^(-t0.5)(d) k is independent of t0.5The question was posed to me by my school principal while I was bunking the class.My question is taken from Reaction Kinetics Elements topic in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» CORRECT answer is (b) k α \(\frac{1}{(t_{0.5})} \) To ELABORATE: For 1^st order REACTION, t0.5 = \(\frac{0.6931}{k}.\) For all REACTIONS of order other than 1, t0.5 = \(\frac{(0.5^{(1-n)}-1)×C_{A0}^{1-n}}{k(1-n)}. \)

Discussion

17.	For the parallel reaction A → B and A → C, of rate constants k1 and k2 respectively, both reactions of order 1, the rate expression is given as ____(a) (-rA) = k1CA + k2CA(b) (-rA) = k1CA – k2CA(c) (-rA) = k2CA(d) (-rA) = k1CAThe question was asked by my college director while I was bunking the class.Origin of the question is Reducing the Size of Kinetic Models topic in portion Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Correct OPTION is (a) (-rA) = k1CA + k2CA For EXPLANATION I would say: For a zero order reaction, \(\frac{-dC_A}{DT}\) = k1CA + k2CA A forms two products: B and C. The CONCENTRATION of A decreases as the reaction progresses.

Discussion

18.	For a first order reaction, the rate constant is expressed in terms of initial concentration CAo and final concentration CA as ____(a) CA = CAo × k(b) CA = CAo × e^-kt(c) CA = CAo × kt(d) CA = CAo × e^ktThis question was posed to me in an online interview.My question is taken from Reaction Kinetics Elements in section Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The CORRECT choice is (B) CA = CAo × e^-kt The EXPLANATION: (\(\frac{-DC}{dt}\)) = kCA ln(\(\frac{CAo}{CA}\)) = kt CA = CAo × e^-kt

Discussion

19.	State true or false.Gas phase decomposition of N2O follows first order mechanism for low concentrations of N2O and second order mechanism for high concentrations of N2O.(a) Gas phase decomposition of N2O follows first order mechanism for low concentrations of N2O and second order mechanism for high concentrations of N2O.(b) True(c) FalseThis question was addressed to me during an interview for a job.I need to ask this question from Reducing the Size of Kinetic Models topic in division Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» The correct CHOICE is (a) Gas phase decomposition of N2O FOLLOWS first order mechanism for LOW concentrations of N2O and second order mechanism for high concentrations of N2O. The explanation: The rate expression is, rN2 = \(\frac{k_1 NO_2^2}{1+kNO_2} \) At low concentrations of N2O, kNO2 << 1 and the REACTIONS follows second order. At high concentrations of N2O, kNO2 >> 1 and the reaction follows first order.

Discussion

20.	State true or false.The Arrhenius law plot of lnk vs 1/ T gives a straight line with large slope for large activation energy.(a) True(b) FalseI have been asked this question during an interview.This intriguing question originated from Reaction Kinetics Elements in portion Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» RIGHT CHOICE is (a) True For EXPLANATION: The plot of lnk VS 1/ T gives a straight line of slope –\(\FRAC{E_a}{(R×T)}\). As Ea increases, slope increases.

Discussion

21.	For any order n, the rate constant is expressed as ____(a) (-rA)(b) (-rA) × CA^n(c) (-rA) × CA(d) \(\frac{-r_A}{C_A^n} \)I have been asked this question during an online exam.I'm obligated to ask this question of Reaction Kinetics Elements topic in chapter Elements of Reaction Kinetics of Chemical Reaction Engineering
Answer» Right option is (d) \(\frac{-r_A}{C_A^n} \) For explanation I would SAY: For any order n, (-RA) = kCA^n. Hence, K = \(\frac{-r_A}{C_A^n}. \)

Discussion

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The unit of activation energy is ____(a) mol(b) mol.K(c) K(d) J/ molThis question was posed to me in quiz.The query is from Reaction Kinetics Elements topic in chapter Elements of Reaction Kinetics of Chemical Reaction Engineering