Reaction Engineering (Set 4) Flashcards
Concepts necessary for reactor design, operation, and maintenance.
The minimum energy required to allow a chemical reaction to proceed is termed as the ‘threshold energy ‘. Chemical reaction with low activation energy are
insensitive to temperature changes.
If Thiele modulus is ____ , then the pore diffusion resistance in a catalyst may be considered as negligible.
< 0.5
From collison theory, the reaction rate constant is proportional to
T^rn.exp(-E/RT)
For a mixed flow reactor operating at steady state, the rate of reaction is given by
FAo/V . XA
Catalytic action in a catalytic chemical reaction follows from the ability of catalyst to change the
activation energy
In Langmuir treatment of adsorption,
whole surface of the catalyst is essentially uniform and the adsorbed molecule has no effect on the rate of adsorption per site.
Organic catalysts differ from the inorganic catalyst in the sense that the former is
proteinous in nature.
An endothermic aqueous phase first order irreversible reaction is carried out in an adiabatic plug flow reactor. The rate of reaction
is maximum at the inlet of the reactor.
Pick out the wrong statement.
A catalyst increases the potential energy barrier over which the reactants must pass to form products.
For an ideal plug flow reactor, the value of Peclet number is
0
An endothermic second order reaction is carried out in an adiabatic plug flow reactor. The rate of heat generation is
maximum at the inlet of the reactor.
Equilibrium of a chemical reaction as viewed by kinetics is a ____ state.
dynamic steady
The conversion in a mixed reactor/accomplishing a reaction A –>3R is 50% when gaseous reactant ‘A’ is introduced at the rate of 1 litre/second and the leaving flow rate is 2 litres/second. The holding time for this operation is ____ second.
0.5
The size of plug flow reactor (PFR) for all positive reaction orders and for any given duty, is ____ that of mixed reactor.
smaller than
A space time of 3 hours for a flow reactor means that
the time required to process one reactor volume of feed (measured at specified conditions) is 3 hours.
If the time required for half change is inversely proportional to the square of initial concentration and the velocity depends on the units in which the concentration term is expressed, then the order of reaction is
3
The experimentally determined overall order of the reaction, A + B –> C + D, is two. Then the
reaction is elementary with a molecularity of 2.
In a continuous flow stirred tank reactor, the composition of the exit stream
is same as that in the reactor.
Recycling back of outlet stream to the reactor from an ideal CSTR carrying out a first order liquid phase reaction will result in ____ in conversion.
no change
The energy balance equation over a tubular reactor under transient conditions is
a linear partial differential equation.
Which of the following factors control the deactivation of a porous catalyst pellet ?
All (a), (b) and (c).
For the reaction, A + B –>2B + C,
rA = -rB
Transition state theory gives the rate constant as
K α T . e^-E/RT
A liquid phase reaction is to be carried out under isothermal conditions. The reaction rate as a function of conversion has been determined experimentally and is shown in the figure given below. What choice of reactor or combination of reactors will require the minimum overall reactor volume, if a conversion of 0.9 is desired ?
PFR followed by a CSTR
Pick out the wrong statement.
Activation energy for a reaction is obtained from the intercept of the Ar-rhenious plot.
In a reversible reaction, a catalyst increases the rate of forward reaction
and the backward reaction equally.
Maximum equilibrium conversion for endothermic reaction is obtained at the ____ temperature.
highest possible
When an exothermic reversible reaction is conducted adiabatically, the rate of reaction
continuously decreases.
For a first order chemical reaction in a porous catalyst, the Thiele modulus is 10. The effectiveness factor is approximately equal to
0.1
The rate equation for the reaction represented by https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/455-245-1.png , is given by - rx = K1 . Cx/(1 + K2 Cx). At high value of Cx (i.e.., K2Cx > > 1), the order of the reaction and the rate constant are respectively
zero order & K1/K2
In solid catalysed reactions the diffusional effects are more likely to affect the overall rate of reaction for
fast reaction in catalyst of large pore diameter.
Helium-mercury method can be used to determine the ____ of the catalyst particle.
all (a), (b), & (c).
For the chemical reaction X –> Y, it is observed that, on doubling the concentration of ‘X’, the reaction rate quadruples. If the reaction rate is proportional to Cxn, then what is the value of ‘n’ ?
4
Chemical reaction rate of a component depends upon the
all (a), (b) and (c).
In a semi-batch reactor
velocity of reaction can be controlled.
A trickle bed reactor is the one, which
employs all the three phases (i.e.. .solid, liquid and gas).
What is the order of a chemical reaction in which doubling the initial concentration of the reactants doubles the half life time of the reaction ?
0
The excess energy of the reactants required to dissociate into products is known as the ____ energy.
activation
In a/an ____ vessel, the fluid enters and leaves following plug flow.
closed
Shift conversion reaction
converts CO to CO2 with steam.
The importance of diffusion in a catalyst are increased by
all (a), (b) and (c).
A back mix reactor is
same as ideal stirred tank reactor.
Which one is the rate controlling step in a solid-gas non-catalytic reaction occurring at very high temperature?
Film diffusion
The rate of the heterogenous catalytic reaction A(g) + B(g) –>C(g) is given by -rA = k.KA.pA.PB/(1 + KA.PA + Kc.pc), where KA and Kc are the adsorption equilibrium constants. The rate controlling step for this reaction is
surface reaction between absorbed A and B in the gas phase.
For a ____ order chemical reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-168-1.png , the half life period is independent of the initial concentration of the reactant A.
first
The ratio of moles of a reactant converted into the desired product to that converted into unwanted product is called
selectivity
The response curve for a step input signal from a reactor is called C-curve. The variance of C-curve in a ‘tanks in series model’ comprising of ‘m’ tanks is equal to
1/m
The eddy diffusivity for a liquid in plug flow must be
0
For multiple reactions, the flow pattern within the vessel affects the
both (a) and (b)
The rate expression for the gaseous phase reaction, CO + 2H2 –> CH3OH, is given by, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/477-488-1.png . Which of the following is not possible ?
α = 1, β = 1, γ =1
For the same residence time, which one will give the maximum conversion ?
Single tubular flow reactor (v = 5 litres).
____ gas is normally employed in B.E.T.method of finding out the surface area of catalyst.
N2
The exit age distribution curve E(t) for an ideal CSTR with the average residence time, τ, is given by
[(e^-t/τ)/T]
The rate constant of a reaction depends on the
temperature of the system.
For the reversible reaction A <–>2B, if the equilibrium constant K is 0.05 mole/litre; starting from initially 2 moles of A and zero moles of B, how many moles will be formed at equilibrium ?
0.338
For identical flow rate and feed composition, X plug flow reactors (PER) in series with a total volume V gives the same conversion as single
PFR of volume V
Time required for 50% decomposition of a liquid in an isothermal batch reactor following first order kinetics is 2 minutes. The time required for 75% decomposition will be about ____ minutes.
4
For a ____ order reaction, the units of rate constant and rate of reaction are the same.
zero
In case of staged packed bed reactors carrying out exothermic reaction, use
all (a), (b) and (c).
Vegetable oils are hydrogenated in a ____ reactor.
slurry
Pure A in gas phase enters a reactor 50% of this A is converted to B through the reaction, A –> 3B. Mole fraction of A in the exit stream is
45294
The rate of reaction does not decrease appreciably as the reaction proceeds in case of ____ reactions.
autocatalytic
For all positive reaction orders for a particular duty,
mixed reactor is always larger than the plug-flow reactor.
The heat of reaction
is independent of the mechanism of reaction.
Which of the following does not produce a change in the value of rate constant of a reaction ?
Concentration and catalyst
With increase in temperature, the equilibrium conversion of a reversible exothermic reaction
decreases
In a CSTR ____ varies with time.
a. reaction rate
b. concentration
c. both (a) & (b)
d. neither (a) nor (b)
neither (a) nor (b)
The following gas phase reactions are carried out isothermally in a CSTR.
A –> 2R ; r1 = k1pA ;
k1 = 20mole/(sec.m3 bar)
A –> 3S ; r2 = k2 pA ;
k2 = 40mole/(sec.m3 .bar)
What is the maximum possible value of FR(mole/sec.) ?
45325
As the chemical reaction proceeds, the rate of reaction
decreases.
Pick out the wrong statement.
A catalyst initiates a reaction.
In a first order reaction, the time required to reduce the concentration of reactant from 1 mole/litre to 0.5 mole/litre will be ____ that required to reduce it from 10 moles/litre to 5 moles/litre in the same volume.
same as
Photo-chemical reactions occur in presence of
sunlight.
n’ number of plug flow reactors (P.F.R) in series with a total volume ‘V’ gives the same conversion as one P.F.R. of volume
V
Knudsen diffusion is directly proportional to
sqrt(T)
Fractional conversion ____ for an exothermic reversible chemical reaction, when the temperature is maximum.
decreases
Non-catalytic fluid-solid reactions are represented by ____ model.
both (a) and (b)
continuous reaction & unreacted core
A pulse tracer is introduced in an ideal CSTR (with a mean residence time ι) at time, t = 0. The time taken for the exit concentration of the tracer to reach half of its initial value will be
2τ
On application of pressure to the equilibrium system, ice <–> water ; which of the following phenomenon will occur ?
More water will be formed.
Participation of ____ is involved in the occurrence of a chemical reaction.
electrons
Promoter.
increases the number of active centres by increasing the unevenness of catalyst surface and by creating discontinuities in the crystals.
The rate constant of a reaction is a function of the
temperature of the system.
Mean residence time is equal to the space time, when
all (a), (b) and (c).
If ‘n’ is the order of reaction, then unit of rate constant is
1/(time)(concentration)^n - 1
Batch process is preferred over continuous process, when the
all (a), (b) & (c)
The value of ‘n’ for a chemical reaction A –> B, whose reaction rate is –>CAn, will be ____ if the rate of the reaction increases by a factor of 8, when the concentration of is doubled.
3
With the same reaction time, initial concentration and feed rate, the reaction 2A –>B is carried out separately in CSTR and P.F. reactor of equal volumes. The conversion will be
higher in P.F. reactor
For any reaction, we may write conversion as a function of
all (a), (b) & (c)
The use of space time is preferred over the mean residence time in the design of a/an
ideal tubular-flow reactor
Autocatalytic reactions are best carried out in a
recycle reactor
The gas phase reaction 2A <–> B is carried out in an isothermal plug flow reactor. The feed consists of 80 mole % A and 20 mole % inerts. If the conversion of A at the reactor exit is 50%, then CA/CA0 at the outlet of the reactor is
45420
A batch reactor suffers from following disadvantage.
All (a), (b)and(c).
A first order reaction is to be treated in a series of two mixed reactors. The total volume of the two reactors is minimum, when the reactors are
equal in size.
A second order liquid phase reaction, A –>B, is carried out in a mixed flow reactor operated in semi batch mode (no exit stream). The reactant A at concentration CAF is fed to the reactor at a volumetric flow rate of F. The volume of the reacting mixture is V and the density of the liquid mixture is constant. The mass balance for A is
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/479-499-4.png
Half life period of a chemical reaction is proportional to CA0-1 , if the reaction is of ____ order.
second
The irreversible reaction, X –> Y, is the special case of the reversible reaction, X <–>Y, in which the
all (a), (b) and (c).
The equilibrium constant K of a chemical reaction depends on
temperature only.
The reaction rate almost gets doubled for 10°C rise in temperature. This is due to the fact that the
fraction of molecules having threshold energy increases.
Which of the following is not a unit of reaction rate ?
None of these
Brunaur, Emmet and Teller (BET) equation is used to determine the specific surface area of a porous particle but not the pore volume & the porosity of the catalyst bed. Which of the following postulates is not used to derive BET equation ?
There is no dynamic equilibrium between successive layer.
The sequence in which three CSTR’s of volumes 5, 10 and 15 m3 will be connected in series to obtain the maximum production in a second order irreversible reaction is
15, 10, 5
