Reaction Engineering (Set 3) Flashcards
Concepts necessary for reactor design, operation, and maintenance.
An isothermal aqueous phase reversible reaction, P <–> R, is to be carried out in a mixed flow reactor. The reaction rate in k.mole/m3 .h is given by, r = 0.5CP - 0.125CR. A stream containing only P enters the reactor. The residence time required (in hours) for 40% conversion of P is
1.6
Design of heterogeous catalytic reactor involves consideration of ____ steps.
both (a) & (b)
chemical & physical
A consecutive reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/446-133.png (A (C1) → B (C2) → C), is characterised by
maxima in the concentration of B.
What is the unit of the rate constant in a chemical reaction in which 10% of the reactant decomposes in one hour, 20% in two hours, 30% in three hours and so on ?
Litre/mole.second
For a fluidised bed reactor, the most suitable/relevant model is a ____ model.
bubbling bed
The rate at which a chemical substance reacts is proportional to its
active mass
In a reaction, the threshold energy is equal to (where, A = activation energy N = normal energy of reactants)
A+N
Thermodynamic equilibrium constant in a system is affected by
temperature
The most suitable reactor for carrying out an auto-thermal reaction is a
CSTR
Which of the following chemical reactions will be favoured by low pressure ?
N2O2 <–> 2NO2
A catalyst in a chemical reaction
all (a), (b) and (c).
Slurry reactors are characterised by the
both (a) and (b).
Limiting reactant in a chemical reaction decides the
conversion
Consider the ‘n’ th order irreversible liquid phase reaction A –> B. Which one of the following plots involving half life of the reaction (t1/2) and the initial reactant concentration (CA0) gives a straight line plot ?
CA0 Vs ln t1/2
The rate of forward reaction, at chemical equilibrium is____the rate of backward reaction.
equal to
Pick the WRONG design guideline for a reactor in which the reactions, A –>R (desired) and A –> S (undesired) are to take place. The ratio of the reaction rates is https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/478-493-1.png .
avoid recycle, when a > b.
With increase in temperature, the equilibrium ____ rises in case of endothermic reaction.
conversion
In case of a consecutive unimolecular type first order reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-170-1.png , the concentration of component ____ increases continuously with time.
S
Enzymes (a protein) are catalysts found in organisms. Its efficiency of catalysing a reaction is due to its capacity to lower the activation energy of the reaction. The enzyme ptyalin used for food digestion is present in
saliva
Considering the endotheomic dissociation of CaCO3 in a closed vessel (CaCO3 <–>CaO + CO2), the pressure of CO2 increases, if
the temperature is increased.
The exit age distribution of fluid leaving a vessel is used to know the
extent of non-ideal flow in the vessel.
From Arhenius law, a plot of loge K versus 1/T gives a straight line with a slope of (-E/R). The unit of E/R is
°K
In the converter of the contact process for the manufacture of H2SO4 the equilibrium conversion of SO2 ____ (A) ____ with increase in temperature and ____ (B) ____ with increase in the mole ratio of SO2 to air.
(A) decreases (B) increases
For the irreversible elementary first order reaction in parallel viz. https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/455-248-1.png , a plot of Cy Vs. Cz will give a straight line having a slope of
K1/K2
The time needed to achieve the same fractional conversion for particles of different sizes (d) when chemical reaction controls, is proportional to
d
A balanced chemical reaction equation conforms to the law of
conservation of mass
An exothermic reaction takes place in an adiabatic reactor. The product temperature ____ reactor feed temperature.
is always greater than
Reverse reaction in a chemical equilibrium is favoured by the
increase in the concentration of oneof the products.
The equilibrium constant for the reversible reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-174-1.png , is affected by the
pressure of the system.
Sum of the powers of the concentration terms in the rate equation is called the ____ of the reaction.
overall order
During manufacture of H2SO4, the oxidation of SO2 to SO3 by oxygen is an en-dothermic reaction. The yield of SO3 will be maximised, if the
temperature is reduced and pressure is increased.
The role of a catalyst in a chemical reaction is to change the
activation energy
The vessel dispersion number (D/μL) for plug flow is
0
Molecularity of a reaction
both (b) and (c).
BET apparatus is used to determine the
specific surface of a porous catalyst.
Carrier in a catalyst increases its
surface area
When the reaction is dominated by in-traparticle diffusion, the apparent order of reaction (nD) as measured is related to the true order (n) as
nD = (n+1)/2
When the reaction occurs in the diffusion controlled region, the apparent activation energy as measured is only ____ the true value.
half
An isothermal irreversible reaction is being carried out in an ideal tubular flow reactor. The conversion in this case will ____ with decrease in space time.
decrease
An elementary liquid phase decomposition reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/476-479-1.png is to be carried out in a CSTR. The design equation is
kτ = XA/(1 - XA)
Kinetics of a solid catalysed reaction can best be studied in a ____ reactor.
mixed
According to Arhenious equation of temperature dependency of rate constant for an elementary reaction
k ∝ e^-E/RT
The reactions of high molecularity are rare, because
of low probability of many body collisions.
Which of the following is the most suitable for isothermal operation ?
Back-mix reactor
For a first order chemical reaction, the rate constant
has unit of time-1.
Which of the following is an autocatalytic reaction ?
Microbial fermentation reaction
The performance of a cascade of CSTR’s can be improved by adding
more CSTR’s in series.
A multiple reaction may be classified as a ____ reaction.
all (a), (b) and (c)
Holding time for flow reactors is ____ the space time, for constant fluid density
equal to
Pick out the wrong statement.
In general, the rate of a reaction becomes triple for every 10°C rise in temperature.
The order of the reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/448-162-1.png , is
0
Arhenious equation shows the variation of ____ with temperature.
rate constant
When a catalyst increases the rate of chemical reaction, the rate constant
increases
In which of the following reactions, the equilibrium will shift to the right, if the total pressure is increased?
N2 + O2 <–> 2NO
The catalyst in a first order chemical reaction changes the
activation energy
Oil is hydrogenated using nickel catalyst in a ____ reactor.
slurry
The performance equations for constant density systems are identical for
P.F.R. and batch reactor.
Reaction rate of a first order reaction, which is half completed in 23 minutes will be
0.03 min-1
Which of the following is the optimum operating condition for an exothermic reversible reaction taking place in a plug-flow reactor ?
Temperature should be high in the beginning and decreased towards the end of the reaction.
The half life period ‘t’ of a zero order reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-168-1.png , is equal to
CA0/2K
The point selectivity of the product ‘Y’ in the reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/458-295-1.png is equal to
K1/K2
In case of calcination of limestone, CaCO3 CaO + CO2, the addition of more of CaO will result in ____ in the concentration of CO2.
no change
The rate of a homogeneous reaction is a function of
all temperature, pressure and composition.
In the fluid catalytic cracker (FCC), the cracking reaction is ____ (A) and the regeneration is___(B) ____
(A) endothermic (B) exothermic
Pick out the correct statement.
A catalyst does not change AH of the reaction.
Promoter is added to the catalyst to improve its
sensitivity
An irreversible first order reaction is being carried out in a CSTR and PFR of same volume. The liquid flow rates are same. The relative conversion will
be more in PFR than in CSTR.
When a high liquid hold up is required in a reactor for gas liquid reaction, use ____ coloumn.
bubble
In an exothermic reaction, the energy of the reacting substances as compared to that of products is
more
For a tubular flow reactor with uniform concentration and temperature, the independent variable is
length
Pick out the wrong statement.
For a first order consecutive reaction, a tubular flow reactor as compared to a stirred tank reactor provides higher overall selectivity.
The first order gas phase reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-470-1.png is conducted isothermally in batch mode. The rate of change of conversion with time is given by
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-470-4.png
The extent of a reaction is
all of the above.
Higher free energy of activation of a chemical reaction (at a given temperature) implies
slower rate of reaction.
Calcination reaction of limestone (CaCO3 –> CaO + CO2) goes to completion in the rotary kiln, because
CO2 escapes continuously.
The reactions with low activation energy are
fast
Molecularity of an elementary reaction, P + Q –> R + S is
4
Which of the following is not endothermic in nature ?
Combustion of sulphur.
The rate of an autocatalytic reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/467-388-1.png , is given by -rA = k . CA . CB. In this case, the
both ‘b’ & ‘c’
The space time is equivalent to the holding time in a steady state mixed reactor for
constant fluid density systems.
The dispersion number of perfect mixed flow is
∞
For the reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/454-239-1.png , the rate of formation of Z is 0.2 gm mole/litre.hr. what is the rate of disappearance of X in gm mole/litre. hr ?
0.4
An irreversible aqueous phase reaction, A + B –> P, is carried out in an adiabatic mixed flow reactor. A feed containing 4kmole/m3 of each A and B enters the reactor at 8m3 /hr. If the temperature of the exit stream is never to exceed 390 K, what is the maximum inlet feed temperature allowed?
Data: Heat of reaction = - 50 kJ/mole
Density of the reacting mixture = 1000kg/m3
Specific heat of reacting mixture = 2kJ/kg.K
The above data can be assumed to be independent of temperature and composition.
290
For a heterogenous catalytic reaction, A + B –> C, with equimole feed of A and B, the initial rate - rA0 is invariant with total pressure. The rate controlling step is
desorption of C.
Half life period of a first order irreversible reaction A B is
ln 2/k
Pick out the wrong statement.
Hydrolysis of ester in presence of alkali or acid is a zero order reaction.
Which of the following is not a dimension-less group used in catalysis ? (where, D = dispersion co-efficient, cm2 /sec.D1 = diffusion co-efficient; cm2/sec L = length of the reactor, cm t = time, sec, v = volumetric flow rate, cm3/sec . V = volume, cm3.)
None of these
Pick out the wrong statement
The mechanism for the decomposition of CH3CHO into CH4 and CO in presence of I2 is:
CH3CHO +I2 –> CH3I + HI + CO; slow
CH3I + HI –> CH4 + I2; fast
Then the rate of disappearance of CH3CHO is equal to K.CCH3I.CHI and acts as a catalyst.
The energy of activation of a chemical reaction
is the minimum energy which the molecules must have before the reaction can take place.
Chemical kinetics can predict the ____ of a chemical reaction.
rate
Which of the following fixes the volume of a batch reactor for a particular conversion and production rate?
Density of mixture
Volume change for unimolecular type first order reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-172-1.png , increases ____ with time.
exponentially
Half life period of decomposition of a liquid ‘A’ by irreversible first order reaction is 12 minutes. The time required for 75% conversion of ‘A’ is ____ minutes.
24
Decomposition rate of a liquid ‘X’ which decomposes as per the reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/456-270-1.png is given by
(K1 + K2)CX
With increase in the space time of an irreversible isothermal reaction being carried out in a P.F. reactor, the conversion will
increase
A catalyst promoter
improves the activity of a catalyst.
In case of a P.F.R., there
both (a) and (b).
For the non-catalytic reaction of particles with surrounding fluid, the time needed to achieve the same fractional conversion for particles of different but unchanging sizes is proportional to the square of particle diameter, when the ____ is the controlling resistance.
diffusion through ash layer
If ΔG (free energy change) for a chemical reaction is very large and negative, then the reaction is
very much feasible.
In a zero order reaction, reactants concentration does not change with time and the
time for half change is half the time taken for completion of the reaction.
