Chemical Reaction Engineering Flashcards
Which of the following will give maximum gas conversion ?
Semi-fluidised bed reactor
__________ explains the mechanism of catalysis.
Activated complex theory
From among the following, choose one which is not an exothermic process.
Catalytic cracking
The fractional volume change of the system for the isothermal gas phase reaction, A 3B , between no conversion and complete conversion is
2
A catalyst
lowers the activation energy of reacting molecules
For high conversion in a highly exothermic solid catalyzed reaction, use a __________ bed reactor.
fluidised bed reactor followed by a fixed
For every 10°C rise in temperature, the rate of chemical reaction doubles. When the temperature is increased from 30 to 70°C, the rate of reaction increases __________ times.
16
The single parameter model proposed for describing non-ideal flow is the __________ model.
both (a) & (b)
A first order reaction requires two equal sized CSTR. The conversion is
more when they are connected in series.
The most unsuitable reactor for carrying out reactions in which high reactant concentration favours high yields is
backmix reactor
Pick out the wrong statement pertaining to space velocity of flow reactors.
The space velocity of 3 hr-1 means that one third reactor volume of feed at specified conditions are being fed into the reactor.
A reactor is generally termed as an autoclave, when it is a
high pressure batch reactor.
6 gm of carbon is burnt with an amount of air containing 18 gm oxygen. The product contains 16.5 gms CO2 and 2.8 gms CO besides other constituents. What is the degree of conversion on the basis of disappearance of limiting reactant ?
95%
The rate constant of a chemical reaction decreases by decreasing the
temperature
__________ is the response curve for a step input signal from a reactor.
S-curve
‘If the catalyst pore size is small in comparison with the mean free path, collisions with the pore wall controls the process’. The diffusivity under this condition is called ‘Knudsen diffusivity’, which is affected by the
temperature
Which of the following is the most suitable for very high pressure gas phase reaction ?
Tubular flow reactor
The reaction between oxygen and organic material is a/an __________ reaction.
exothermic
With decrease in temperature, the equilibrium conversion of a reversible endother-mic reaction
decreases
In an exothermic chemical reaction, the reactants compared to the products have
more energy
A reversible liquid phase endothermic reaction is to be carried out in a plug flow reactor. For minimum reactor volume, it should be operated such that the temperature along the length
is at the highest allowable temperature throughout.
A batch reactor is suitable for
liquid phase reactions
For a heterogeneous catalytic reaction
free energy of activation is lowered in the presence of catalyst, which remains unchanged at the end of reaction
free energy of activation is lowered in the presence of catalyst, which remains unchanged at the end of reaction
decrease in activation energy.
A catalyst loses its activity due to
all (a), (b) and (c)
N’ plug flow reactors in series with a total volume ‘V’ gives the same conversion as a single plug flow reactor of volume ‘V’ for __________ order reactions.
any
Specific rate constant for a second order reaction
both (b) and (c).
For a zero order chemical reaction, the
all (a), (b) and (c).
Radioactive decay follows __________ order kinetics.
first
The excess energy of reactants in a chemical reaction required to dissociate into products is termed as the __________ energy.
activation
For a solid catalyzed chemical reaction, the effectiveness of solid catalyst depends upon the __________ adsorption.
chemical
Pick out the correct statement.
A catalyst lowers the activation energy of the reacting molecules.
The dimensions of rate constant for reaction 3A B are (l/gm mole)/min. Therefore the reaction order is
2
Pick out the correct statement
Reactions with high activation energies are very temperature sensitive.
If the time required to complete a definite fraction of reaction varies inversely as the concentration of the reactants, then the order of reaction is
2
Sulphuric acid is used as a catalyst in the
alkylation of hydrocarbons.
Fractional conversion __________ with increase in pressure for ammonia synthesis reaction i.e., N2 + 3H2 2NH3.
increases
Pick out the wrong statement.
Mixed reactor is always smaller than the plug flow reactor for all positive reaction orders for a particular duty.
The reason why a catalyst increases the rate of reaction is that, it
decreases the energy barrier for reaction.
A first order irreversible reaction, A B is carried out separately in a constant volume as well as in a variable volume reactor for a particular period. It signifies that __________ in the two reactors.
conversion in both will be the same but concentrations will be different
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
In an ideal tubular-flow reactor
all (a), (b) and (c).
__________ is the controlling step in a highly temperature sensitive fluid-solid non-catalytic reaction.
Chemical reaction
An autothermal reactor is
completely self-supporting in its thermal energy requirements.
The rate constant of a first order reaction depends on the
temperature.
A reaction in which one of the products of reaction acts as a catalyst is called a/an __________ reaction.
autocatalytic
Conversion increases with increase in temperature in case of a an __________ reaction.
reversible endothermic
A photochemical reaction is __________ light.
initiated by
Pick out the wrong statement.
In a continuous flow reactor, uniform concentration can not be maintained throughout the vessel even in a well agitated system.
In a/an __________ reactor, there is exchange of heat with the surroundings with sizeable temperature variation.
non-adiabatic
‘Unreacted core model’ represents the reaction involving
roasting of sulphide ores.
If a solid-gas non-catalytic reaction occurs at very high temperature, the rate controlling step is the __________ diffusion.
film
The units of frequency factor in Arhenious equation
are the same as those of the rate constant.
Which of the following is not a chemical step in a fluid solid catalytic reaction
none of these
In case of __________ reactions, the reaction rate does not decrease appreciably as the reaction proceeds.
auto catalytic
For nearly isothermal operation involving large reaction time in a liquid-phase reaction, the most suitable reactor is a __________ reactor.
stirred tank
B.E.T. method can be used to determine the __________ of a porous catalyst.
surface area
Which of the following is an independent variable for a batch tank reactor with uniform concentration and temperature ?
Time
For reactions in parallel viz A P (desired product) and A Q (unwanted product), if the order of the desired reaction is higher than that of the undesired reaction, a
both (a) and (b).
In a reversible chemical reaction having two reactants in equilibrium, if the concentration of the reactants are doubled, then the equilibrium constant will
remain the same
The equilibrium constant of a catalytic chemical reaction __________ due to the presence of a catalyst
remains unaffected
The rate constant of a chemical reaction increases by increasing the
temperature
The catalytic activity of enzymes is due to their capacity to lower the __________ energy.
activation
A first order reaction requires two unequal sized CSTR. Which of the following gives higher yield ?
Either of the arrangement (a) or (b) will give the same yield.
Pick out the correct statement.
A lower temperature favours the reaction of lower activation energy
A batch reactor is characterized by
variation in extent of reaction and properties of the reaction mixture with time.
When a catalyst increases the rate of forward reaction, the value of rate constant
increases
Rate determining step in a reaction consisting of a number of steps in series is the __________ step.
slowest
The rate of a chemical reaction is almost doubled for every 10°C rise in temperature. The rate will increase __________ times, if the temperature rises form 10 to 100°C.
512
A catalyst in a chemical reaction __________ free energy change in the reaction
either (a) or (b); depends on the type of catalyst
Signal normally used to study non-ideal flow by stimulus response technique is __________ input.
both (a) & (b)
When all the limiting reactant is consumed in the reaction, the operational yield __________ the relative yield.
equals
The half life period of a first order reaction is
independent on initial concentration of the reactants.
The catalyst in a second order reversible reaction increases the rate of the forward reaction
and backward reaction equally.
Catalyst carriers
provide large surface area with a small amount of active material.
For the liquid phase zero order irreversible reaction A B, the conversion of A in a CSTR is found to be 0.3 at a space velocity of 0.1min-1 . What will be the conversion for a PFR with a space velocity of 0.2 min-1? Assume that all the other operating conditions are the same for CSTR and PF
0.60
A high space velocity means that a given
both (a) and (b)
In flow reactors, the performance equations interrelate the rate of reaction to the
all (a), (b) and (c).
Space velocity
all (a), (b) and (c)
The rate of the chemical reaction A B doubles as the concentration of A i.e.., CA is doubled. If rate of reaction is proportional to CAn, then what is the value of n for this reaction ?
1
A reaction which is catalysed by a base is catalysed by all substances which have a tendency to
gain a proton
For a homogeneous reaction of nth order, the dimension of the rate constant is given by
(concentration)1 - n/(time)
The fractional volume change between no conversion and complete conversion, for the isothermal gas phase reaction, 2A R, is
-0.5
The reaction in which one of the products of reaction acts as a catalyst is called a/an __________ reaction.
A typical example of an exothermic reversible reaction conducted at high pressure in industry is
autocatalytic
A typical example of an exothermic reversible reaction conducted at high pressure in industry is
dehydration of ethanol.
Study of chemical kinetics is the easiest in the case of __________ reactions.
irreversible
In autocatalytic reactions,
one of the products acts as a catalyst.
Semibatch reactor is preferred, when a/an
all (a), (b), and (c).
Exposure of a photographic plate to produce a latent image is an example of __________ reaction.
both (b) and (c)
For identical flow rate, feed composition and for elementary first order reactions, ‘N’ equal sized mixed reactors in series with a total volume ‘V’ gives the same conversion as a single plug flow reactor of volume ‘V’ for constant density systems. This is true, when the value of ‘N’ is
∞
Helium-mercury method is used for the measurement of the __________ of the catalyst.
both (b) & (c).
What is the order of a chemical reaction whose rate is deter-mined by the variation of one concentration term only ?
first
Pick out the wrong statement.
The order and molecularity of a complex reaction may not be the same.
The rate at which a chemical substance reacts is proportional to its
active mass
A plug-flow reactor is characterized by
presence of lateral mixing.
For a tubular reactor with space time ‘τ’ and residence time ‘θ’, the following statement holds good.
τ = θ , for an isothermic tubular reactor in which the density of the process fluid is constant.
Rate of an autocatalytic chemical reaction is a function of
all (a), (b) and (c).
Which of the following curves shows the effect of temperature on the extent of gas-solid adsorption at a given pressure ?
Adsorption isobar
For an ideal mixed flow reactor (CSTR), the exit age distribution E(t) is given by
none of the above
For series reaction, the relative yield
both (a) and (c) hold good.
Fluid flow in a real packed bed can be approximated as __________ model
dispersion
The ‘E’ curve for a non-ideal reactor defines the fraction of fluid having age between t and t + dt
at the outlet
A reaction which is catalysed by an acid is also catalysed by any substance, which has a tendency to
lose a proton.
lose a proton.
A stirred tank reactor compared to tubular-flow reactor provides
all (a), (b) and (c)
A chemical reaction, A 3B, is conducted in a constant pressure vessel. Starting with pure A, the volume of the reaction mixture increases 3 times in 6 minutes. The fractional conversion is
1
A catalyst inhibitor
all(a), (b) and (c)
In chamber process of sulphuric acid manufacture in industry, the gas phase oxidation of SO2 to SO3 is accomplished by a __________ reaction.
catalytic homogenous
If the rate of a chemical reaction becomes slower at a given temperature, then the
free energy of activation is higher.
Pick out the wrong statement.
A batch reactor can not be used to study the kinetics of catalytic reaction.
For a zero order reaction, the concentration of product increases with the
increase of reaction time.
Effectiveness factor of a catalyst pellet is a measure of the __________ resistance.
pore diffusion
The rate expression for a heterogenous catalytic reaction is given by, - rA = K.KA PA(1 + KA.PA + KR.PR), where K is surface reaction rate constant and KA and KR are absorption equilibrium constants of A and R respectively. If KR PR»_space; (1 + KA PA), the apparent activation energy EA is equal to (given E is the activation energy for the reaction and ΔHR and ΔHA are the activation energies of adsorption of R and A)
E + ΔHA - ΔHR)
Differential method for analyzing the kinetic data is used
for testing complicated mechanisms.
In case of the irreversible unimolecular type, first order reaction, the fractional conversion at any time for constant volume system as compared to variable volume system is
same
The reaction in which the rate equation corresponds to a stoichiometric equation, is called a/an __________ reaction.
elementary
__________ catalytic reaction is involved in the thermal cracking of gas oil.
Homogeneous
The reaction A B is conducted in an isothermal batch reactor. If the conversion of A increases linearly with holding time, then the order of the reaction is
0
Arrhenious equation represents graphically the variation between the __________ and temperature.
rate constant
Variables affecting the rate of homogeneous reactions are
pressure, temperature and composition.
A chemical reaction occurs when the energy of the reacting molecules is __________ the activation energy of the reaction
equal to or more than
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
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
With increase in temperature, the rate constant obeying Arrhenius 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 rise in temperature
all (a), (b) and (c).
The enzyme which can catalyze the conversion of glucose to ethyl alcohol is
zymase
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
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 ?
1/2
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.
Inversion of cane sugar is an example of
bimolecular reaction with first order.
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.
Pick out the correct statement.
Pressure changes do not change the equilibrium concentrations.
Integral method for analyzing the kinetic data is used
both (a) and (b).
__________ resistance is not involved in the combustion of a carbon particle.
Ash
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
B.E.T. method of finding out surface area of a catalyst, uses the extension of __________ isotherm.
Langmuir
An example of autothermal reactor operation is
ethylene oxidation
In an ideal P.F.R. at steady state conditions
the conversion of the reactant varies from point to point along a flow path.
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 preferred reacting system for oxidation of o-xylene to phthalic anhydride is
jacketted liquid phase CSTR.
Arhenious equation shows the variation of __________ with temperature.
rate constant
When a catalyst increases the rate of chemical reaction, the rate constant
increases
The catalyst in a first order chemical reaction changes the
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.
The rate of a homogeneous reaction is a function of
all temperature, pressure and composition.
Pick out the correct statement.
A catalyst does not change AH of the reaction.
A catalyst promoter
improves the activity of a catalyst.
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
For the same residence time, which one will give the maximum conversion ?
Single tubular flow reactor (v = 5 litres).
The rate constant of a reaction depends on the
temperature of the system.
The equilibrium constant K of a chemical reaction depends on
temperature only.
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
Which of the following resistances is not involved in a gas phase catalytic (gas-solid) reaction ?
Ash resistance.
If the time required to change the concentration of reactant to half its original value is independent of the initial concentration, the order of reaction is
one
A photochemical reaction is
initiated by light.
