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Chemical Engineering
Chemical Reaction Engineering
Quiz 6
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Q.1
For any reaction, we may write conversion as a function of
Concentration
Time
Temperature
All of the above
Q.2
In flow reactors, the performance equations interrelate the rate of reaction to the
Feed rate
Reactor volume
Extent of reaction
All of the above
Q.3
The space time is equivalent to the holding time in a steady state mixed reactor for
Non-isothermal gas reaction
Variable fluid density systems
Constant fluid density systems
Gas reactions with changing no. of moles
Q.4
Maximum equilibrium conversion for endothermic reaction is obtained at the __________ temperature.
Highest possible
Lowest possible
Intermediate
Room
Q.5
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 C
A
/C
A
0
at the outlet of the reactor is
2/3
5/8
1/3
3/8
Q.6
The molecularity and the order of reaction respectively, for the hydrolysis of methyl acetate in presence of acids are
2 & 1
11 & 2
2 && 2
1 & 1
Q.7
Pick out the wrong statement.
Exit age description function (E) and internal age distribution function (I) are related as,E = - dI/d0 .#
Chmisorption studies are useful in the determination of catalyst surface area and pore size distribution
A higher temperature favours the reaction of higher activation energy
A catalyst increases the potential energy barrier over which the reactants must pass to form products
Q.8
The effectiveness factor for large value of Thiele modulus (L√(K/D1)) of a solid catalysed first order reaction is equal to (where, L = length of the reactor, cm, D1 = diffusion co-efficient, cm²/second)
L√(K/D1)
1/(L√(K/D1))
1
∞
Q.9
Exothermic reactions are best carried out in
A CSTR
CSTR in series
A plug flow reactor followed by CSTR
CSTR followed by a plug flow reactor
Q.10
The residence time distribution of an ideal CSTR is
1/τ exp (-t/τ)
Τ exp (-t/τ)
Exp(-t/τ)
1/τ (-t/τ)
Q.11
To maximise the formation of R in the simultaneous reaction
A + B → R , r
R
= 2C
A
0.5
.C
B
2
A + B → S , r
S
= 1.5 C
A
. C
B
We should have
Low C
A
, low C
B
Low C
A
, high C
B
High C
A
, low C
B
High C
A
, high C
B
Q.12
For a heterogeneous catalytic reaction
Free energy of activation is lowered in the presence of catalyst, which remains unchanged at the end of reaction
A relatively small amount of catalyst can cause the conversion of large amount of reactants which does not mean that catalyst concentration is important
The catalyst does not form an intermediate complex with the reactant
The surface of the catalyst does not play an important role during reaction
Q.13
The performance equations for constant density systems are identical for
P.F.R. and backmix reactor
P.F.R. and batch reactor
P.F.R, batch reactor and backmix reactor
Batch reactor and backmix reactor
Q.14
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 increased
Pressure is reduced
Temperature is increased and pressure is reduced
Temperature is reduced and pressure is increased
Q.15
__________ is the controlling step in a highly temperature sensitive fluid-solid non-catalytic reaction.
Gas film diffusion
Ash diffusion
Chemical reaction
None of these
Q.16
For series reaction, the relative yield
Is always greater for plug-flow reactor than for the single CSTR of the same volume
Statement in A is wrong
Decreases with increasing conversion
Both A and C hold good
Q.17
In a reversible reaction, a catalyst increases the rate of forward reaction
Only
To a greater extent than that of the backward reaction
And decreases that of the backward reaction
And the backward reaction equally
Q.18
A batch reactor suffers from following disadvantage.
Poor product quality control
High labour and handling cost
High shutdown time requirement for emptying, cleaning and refilling
All of the above
Q.19
The reaction rate almost gets doubled for 10°C rise in temperature. This is due to the fact that the
Increased temperature reduces the activation energy
Fraction of molecules having threshold energy increases
Collision frequency increases
Value of threshold energy decreases
Q.20
Participation of __________ is involved in the occurrence of a chemical reaction.
Protons
Neutrons
Electrons
None of these
Q.21
With decrease in temperature, the equilibrium conversion of a reversible endother- mic reaction
Decreases
Increases
Remains unaffected
Increases linearly with temperature
Q.22
The irreversible reaction, X → Y, is the special case of the reversible reaction, X ⇋ Y, in which the
Equilibrium constant is infinite
Fractional conversion of
Concentration of
All of the above
Q.23
Photo-chemical reactions occur in presence of
Sunlight
Darkness
Solid catalysts
Monochromatic radiation only
Q.24
The order of a chemical reaction is
An experimentally determined quantity
Always equal to the total stoichiometric number of reactants
Never fractional
None of these
Q.25
With increase in initial concentration, the fractional conversion of a first order reaction in a given time
Increases
Decreases
Remains constant
Unpredictable
Q.26
'Unreacted core model' represents the reaction involving
Combustion of coal particles
Roasting of sulphide ores
Manufacture of carbon disulphide from elements
None of these
Q.27
If the pore diffusion controls in a catalytic reaction, the apparent activation energy E
a
is equal to
The intrinsic activation energy E
(E + E
D
) where E
D
is activation due to diffusion
(E + E
D
)/2
E
D
/2
Q.28
The rate constant of a reaction depends on the
Initial concentration of reactants
Time of reaction
Temperature of the system
Extent of reaction
Q.29
Shift conversion reaction
Converts N₂ and H₂ into NH₃
Converts CO to CO₂ with steam
Is non-catalytic
Is highly exothermic
Q.30
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.) ?
1/3
1/2
2/3
2
Q.31
When the density of the reaction mixture is constant in a chemical reaction, the ratio of the mean residence time to space time is
> 1
< 1
1
0
Q.32
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
Time for half change is independent of the initial concentration
Time for completion of the reaction is independent of the initial concentration
Reaction rate is trebled when the initial concentration is trebled
Q.33
Pick out the wrong statement.
Autocatalytic reactions are exemplified by microbial fermentation reactions
The slowest step has the greatest influence on the overall reaction rate in case of an irreversible series reaction
He fractional conversion at any time is same for both the constant as well as the variable volume system in case of an irreversible unimolecular type first order reaction
Ydrolysis of ester in presence of alkali or acid is a zero order reaction
Q.34
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/n
V
V.n
1/V
Q.35
For a first order isothermal chemical reaction in a porous catalyst, the effectiveness factor is 0.3. The effectiveness factor will increase if the
Catalyst size is reduced or the catalyst diffusivity is reduced
Catalyst size is reduced or the catalyst diffusivity is increased
Catalyst size is increased or the catalyst diffusivity is reduced
Catalyst size is increased or the catalyst diffusivity is increased
Q.36
In an ideal mixed reactor (at steady state), the
Space time is equivalent to holding time for constant density systems
Composition throughout the reactor remains same
Exit stream has the same composition as the fluid within the reactor
All of the above
Q.37
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
Goes through a maximum along the length of the reactor
Goes through a minimum along the length of the reactor
Is maximum at the exit of the reactor
Q.38
Pick out the wrong statement:
Chemical reactions with high activation energy are very temperature sensitive
A flat velocity profile exists in a plug flow reactor
The residence time for all the elements of fluid in case of a P.F.R. need not be same
Half life of a reaction increases with increased initial concentration for reaction orders more than one
Q.39
The rate of the heterogenous catalytic reaction A(g) + B(g) ? C(g) is given by -r
A
= k.K
A
.p
A
.P
B
/(1 + K
A
.P
A
+ K
c
.p
c
), where K
A
and K
c
are the adsorption equilibrium constants. The rate controlling step for this reaction isA. absorption of A.
Absorption of A
Surface reaction between absorbed A and absorbed B
Surface reaction between absorbed A and B in the gas phase
Surface reaction between A in the gas phase and absorbed B
Q.40
Pick out the wrong statement.
In a multistep reaction, the slowest step is the rate determining step
In general, the rate of a reaction becomes triple for every 10°C rise in temperature
Slow chemical reactions have generally high values of activation energy
Molecularity of a reaction can not be zero but the order of a reaction can be zero
Q.41
Half life period of a chemical reaction is
The time required to reduce the concentration of the reacting substance to half its initial value
Half of the space time of a reaction
Half of the residence time of a reaction
None of these
Q.42
Non-catalytic fluid-solid reactions are represented by __________ model.
Continuous reaction
Unreacted core
Both A and B
Neither A and B
Q.43
On application of pressure to the equilibrium system, ice ⇋ water; which of the following phenomenon will occur?
Water will evaporate
Equilibrium will not be attained
More ice will be formed
More water will be formed
Q.44
"A spherical porous catalyst particle of radius R is subjected to reactant A which reacts to form B by a zero order surface reaction A → B. Film mass transfer resistance is negligible and pore diffusion of A is rate controlling. The effectiveness factor of the catalyst is reported as 7/8. Which of the following statement is true?A. Inner catalyst core of radius R/8 does not participate in reaction."
Inner catalyst core of radius R/8 does not participate in reaction
Inner catalyst core of radius R/2 does not participate in reaction
Inner catalyst core of radius 7R/8 does not participate in reaction
Ffectiveness factor for a zero order reaction can not be 7/8 as it must always be 1
Q.45
Pick out the wrong statement.
Or a first order consecutive reaction, a tubular flow reactor as compared to a stirred tank reactor provides higher overall selectivity
Or an ideal mixed reactor at steady state, the exit stream has the same composition as fluid within the reactor and the space time is equivalent to holding time for constant density system
Lug flow reactor (PFR) is always smaller than mixed reactor for all positive reaction orders for a particular duty
Eaction rate does not decrease appreciably as the reaction proceeds in case of an autocatalytic reaction
Q.46
The synthesis of proteins and metabolism in biological objects occur in the presence of biocatalyst called
A ferment or an enzyme
Haemoglobin
Fungi
None of these
Q.47
The knowledge of initial concentration and rate constant is necessary to determine the half life time of a reaction of __________ order.
Zero
First
Second
None of these
Q.48
The rate of a gas phase reaction is given by K . C
A
. C
B
. If the volume of the reaction vessel is reduced to l/4th of its initial volume, then the reaction rate compared to the original rate will be __________ times.
4
16
8
2
Q.49
Batch process is preferred over continuous process, when the
Product yields and quality can not be achieved in continuous process, because of long residence time
Sales demand of product is not steady
Same equipment can not be used for several processes of the same nature
All of the above
Q.50
Fluid flow in a real packed bed can be approximated as __________ model.
Plug flow
Dispersion
Mixed flow
Tank in series
0 h : 0 m : 1 s
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