Reaction Engineering (Set 5) Flashcards
Concepts necessary for reactor design, operation, and maintenance.
The following half life data are available for the irreversible liquid phase reaction A products.
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/470-419-1.png The overall order of reaction is
1.5
A non-catalytic chemical reaction of the type https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/457-279-1.png is called a ____ reaction.
series-parallel
The unit of frequency factor in Arhenious equation is
same as that of rate constant.
With increase in the order of reaction (for all positive reaction orders), the ratio of the volume of mixed reactor to the volume of plug flow reactor (for identical feed composition, flow rate and conversion)
increases
Reaction of benzene with chlorine gas to produce tri-chlorobenzene exemplifies a/an ____ reaction.
consecutive
For the gaseous reaction 2A –> B, where the feed consists of 50 mole % A and 50 mole % inerts, the expansion factor is
-0.25
The molecularity and the order of reaction respectively, for the hydrolysis of methyl acetate in presence of acids are
2 & 1
The irreversible reaction is a special case of reversible reaction, if the
reactant concentration at equilibrium condition is zero.
A pollutant P degrades according to first order kinetics. An aqueous stream containing P at 2 kmole/m3 and volumetric flow rate 1m3 /h requires a mixed flow reactor of volume V to bring down the pollutant level to 0.5 kmole/m3 . The inlet concentration of the pollutant is now doubled and the volumetric flow rate is tripled. If the pollutant level is to be brought down to the same level of 0.5 kmole/m3 , the volume of the mixed flow reactor should be increased by a factor of
7
For the liquid phase parallel reactions:
R, rR = K1.CA2; E1 = 80 KJ/mole
S, rs= K1.CA ; E2 = 120 KJ/mole
The desired product is R. A higher selectivity of R will be achieved, if the reaction is conducted at
high temperature in a PFR.
In an ideal mixed reactor (at steady state), the
all (a), (b) and (c).
The knowledge of initial concentration and rate constant is necessary to determine the half life time of a reaction of ____ order.
second
Which of the following factors control the design of a fluid-solid reactor ?
All (a), (b) and (c).
A Catalyst
shortens the time to reach the equilibrium.
The reaction rate constants at two different temperature T1 and T2 are related by
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/470-421-2.png
The synthesis of proteins and metabolism in biological objects occur in the presence of biocatalyst called
fungi
Pick out the wrong statement.
The intercept of the Arrhenious plot is called the ‘activation energy’.
Kinetics of a catalytic reaction can be best studied on a/an ____ reactor.
either (a), (b) and (c).
In case of a ____ reactor, the composition in the reactor and at the exit of the reactor is the same.
back-mix
Exothermic reactions are best carried out in
CSTR followed by a plug flow reactor.
What is the order of chemical reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-166-1.png , if itis found that the reaction rate doubles on doubling the concentration of B and also the reaction rate doubles when the concentrations of both A & B were doubled and quandrupled when the concentrations of both B & C were doubled ?
2
Reactions with high activation energy are
very temperature sensitive
If n = overall order of a chemical reaction. a = initial concentration of reactant. t = time required to complete a definite fraction of the reaction. Then pick out the correct relationship.
t ∝ 1/a^n-1
In case of a/an ____ chemical reaction, conversion increases with the rise in temperature.
reversible endothermic
A space velocity of 5 hr-1 means that
five reactor volumes of feed (at specified conditions) are being fed into the reactor per hour.
With increase in initial concentration, the fractional conversion of a first order reaction in a given time
remains constant
The rate of reaction of a/an ____ reaction is not affected by temperature rise.
photochemical
With an increase in pressure in gaseous phase chemical reactions, the fractional conversion ____ when the number of moles decreases.
increases
Half-life period for a first order reaction is ____ the initial concentration of the reactant.
independent of
Carbon particles accummulated on the catalyst used in the gas oil cracking lies in the category of ____ poison.
deposited
The order of the chemical reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/448-163-1.png , whose rate equation is given as -rA= KCA2. CB is
3
What is the dispersion number for a plug flow reactor ?
0
The decomposition of A into B is represented by the exothermic reaction, A <–> 2B. To achieve maximum decomposition, it is desirable to carry out the reaction.
at low P and low T.
The catalytic converter for conversion of SO2 to SO3 by contact process should have a feed with SO2 content between
7-10%
If the pore diffusion controls in a catalytic reaction, the apparent activation energy Ea is equal to
ED/2
With increase in K2/K1 in case of a unimolecular type elementary reactions https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-170-1.png , the fractional yield of ‘R’ in mixed reactor (for a given conversion of ‘A’)
decreases
Collision theory gives the rate constant for bimolecular reaction as
K α e^-E/RT
Find a mechanism that is consistent with the rate equation and reaction given below:
2A + B –> A2B, ( - rA) = k.CA.CB
A + A <–> AA;AA + B –> A2B
A gaseous reactant is introduced in a mixed reactor of 3 litres volume at the rate of 1 litre/second. The space time is ____ seconds.
3
The temperature dependence of reaction rate constant (K) by Arhenius law is given by
K α e^-E/RT
For a ____ order chemical reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-169-1.png , the fractional conversion of reactant ‘A’ is proportional to time.
zero
Velocity of a chemical reaction
a. decreases with increase in temperature.
b. increases with increase of pressure of reactants for all reactions.
c. decreases with increase of reactant concentration.
none of these.
Backmixing is most predominant in
a single CSTR.
If helium is introduced in a reactor containing O2, SO2 and SO3 at equilibrium, so that total pressure increases while volume and temperature remains constant. In this case the dissociation of SO3 (as per Le Chatlier principle)
decreases
Consider a reversible exothermic reaction in a plug flow reactor. The maximum and minimum permissible temperatures are Tmax and Tmin respectively. Which of the following temperature (T) profiles will require the shortest residence time to achieve the desired conversion.
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/478-497-2.png
Fluidised bed reactor is characterised by
uniformity of temperature.
In which of the following gaseous phase reversible reactions, the product yield can not be increased by the application of high pressure ?
N2 + O2 <–> 2NO
Space time equals the mean residence time
when the density of the reaction mixture is constant.
A liquid decomposes by irreversible first order kinetics and the half life period of this reaction is 8 minutes. The time required for 75% conversion of the liquid will be ____ minutes.
16
Rate constant ‘k’ and absolute temperature ‘T’ are related by collision theory (for bimolecular) as
k ∝ sqrt(T)
The conversion for a first order liquid phase reaction. A –> B in a CSTR is 50%. If another CSTR of the same volume is connected in series, then the % conversion at the exit of the second reactor will be
75
What is the dispersion number for a CSTR?
∞
Rate of a chemical reaction is independent of the concentration of the reactants for a ____ reaction.
zero order
With increase in temperature, the rate constant obeying Arhenious equation
increases.
Bulk diffusion in catalyst pore ____ with increase in pressure.
decreases
Pick out the correct statement.
The rate constant for a first order reaction does not change on changing the concentration units.
The concentration of A in a first order reaction, A –> B, decreases
exponentially with time.
The equilibrium constant of chemical reaction ____ in the presence of catalyst.
remains unaffected
The order of a chemical reaction is
an experimentally determined quantity.
A chemical reaction occurs, when the energy of the reacting molecules is ____ the activation energy of reaction.
equal to or more than
In the hydrodealkylation of toluene to benzene, the following reactions occur:
C7H8 + H2 –> C6H6 + CH4
2C6H6 <–> C12H10 + H2
Toluene and hydrogen are fed to a reactor in a molar ratio 1:5.80% of the toluene gets converted and the selectivity of benzene(defined as moles of benzene formed/moles of toluene converted) is 90%. The fractional conversion of hydrogen is
0.144
Catalyst is a substance, which ____ chemical reaction.
can either increase or decrease the speed of a
The residence time distribution of an ideal CSTR is
exp (-t/τ)
A rise in temperature
all (a), (b) and (c).
The enzyme which can catalyse the conversion of glucose to ethyl alcohol is
zymase
For reaction, P + 2 –>3R, molar rate of consumption of P is
half of that of Q.
If pore diffusion is the controlling step in a solid catalysed reaction, the catalyst
porosity is of less importance.
The conversion of a reactant, undergoing a first order reaction, at a time equal to three times the half life of the reaction is
0.875
In case of unimolecular type elementary reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/449-176-1.png , plug flow reactor as compared to mixed reactor is
more
What is the value of ‘n’ if the reaction rate of the chemical reaction A –> B, is proportional to CAn and it is found that the reaction rate triples, when the concentration of ‘A’ is increased 9 times ?
45293
The first order series reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/473-457-1.png is conducted in a batch reactor. The initial concentrations of A, B and C (CA0, CB0, CC0 respectively) are all non-zero. The variation of CB with reaction time will not show a maximum, if
k2 CB0 > k1 CA0
A second order reaction of the form A + B –> C is called a pseudo-first order reaction, when
CB0 ≥ CB0
Pick out the wrong statement.
According to the penetration theory, the mass transfer co-efficient decreases, if the exposure time of an eddy to the solute decreases.
Effectiveness factor (E) of a catalyst pellet is defined as https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/458-294-1.png , Effectiveness factor for a first order reaction is given by (where, T = Thiele modulus)
tan hT/T
Inversion of cane sugar is an example of
bimolecular reaction with first order.
Pick out the correct statement.
Pressure changes do not change the equilibrium concentrations.
In which of the following gaseous phase reactions, the equilibrium of the reaction remains unaffacted by pressure changes ?
N2 + O2 <–> 2NO
The mean conversion in the exit stream, for a second order, liquid phase reaction in a non-ideal flow reactor is given by
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-471-1.png
Integral method for analysing the kinetic data is used
both (a) and (b).
Concentration of the limiting reactant (with initial concentration of a moles/litre) after time t is (a-x). Then ‘t’ for a first order reaction is given by
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/437-12-1.png
The rate of a gas phase reaction is given by K . CA . CB. 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.
16
Rate of a chemical reaction is not affected by the
number of molecules of reactants taking part in the reaction.
Overall rate of reaction in a heterogenous catalytic reaction depends upon the mass and energy transfer from the fluid to solid surface and its rate of reaction is usually ____ the concentration of catalyst, if it does not entail a chain mechanism.
proportional to
____ resistance is not involved in the combustion of a carbon particle.
Ash
In an ideal P.F.R. at steady state conditions
the conversion of the reactant varies from point to point along a flow path.
B.E.T. method of finding out surface area of a catalyst, uses the extension of ____ isotherm.
Langmuir
In a chemical reaction, repesented by, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/454-241-1.png , it is observed that the
(i) rate of reaction increases by a factor of 4 on doubling the concentration of the reactant.
(ii) rate of reaction increases by a factor of 9 on trebling the concentration of the reactant.
Then the rate of the reaction is proportional to(where, CA = contentration of the reactant)
CA^2
Which of the following holds good for an elementary reaction,https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/455-249-1.png ?
Three times the rate of disappearance of ‘X’ is equal to the rate of appearance of ‘Z’.
An example of autothermal reactor operation is
ethylene oxidation
For a packed bed reactor; the presence of a long tail in the residence time distribution curve is an indication of
dead zone
Space time in flow reactor is
both (a) and (b).
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 increased.
Cold shot cooling is only practical when the feed temperature is ____ than the reaction temperature.
much lower
The following gas phase reaction is taking place in a plug flow reactor. https:/ /www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/478-498-1.png
A stoichiometric mixture of A and B at 300 K is fed to the reactor. At 1 m along the length of the reactor, the temperature is 360 K. The pressure drop is negligible and an ideal gas behaviour can be assumed. Identify the correct expression relating the concentration of A at the inlet (CA0), concentration of A at 1m (CA) and the corresponding conversion of A (X).
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/479-498-3.png
The preferred reacting system for oxidation of o-xylene to phthalic anhydride is
jacketted liquid phase CSTR.
The effectiveness factor for large value of Thiele modulus (L.sqrt(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)
1/L(sqrt(K/D1))
A first order reaction A B occurs in an isothermal porous catalyst pellet of spherical shape. If the concentration of A at the centre of the pellet is much less than at the external surface, the process is limited by
diffusion within the pellet.
Following isothermal kinetic data are obtained in a basket type of mixed flow reactor for a porous catalyst. Determine the role of pore diffusion and external mass transfer processes. https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/477-486-1.png
Strong pore diffusion control and mass transfer not controlling.
