Reaction Engineering (Set 1) Flashcards
Concepts necessary for reactor design, operation, and maintenance.
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.
What is the order of a chemical reaction, A + 2B (K)→ C, if the rate of formation of ‘C’, increases by a factor of 2.82 on doubling the concentration of ‘A’ and increases by a factor of 9 on trebling the concentration of ‘B’?
7/2
For high conversion in a highly exothermic solid catalysed 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.
a. tank in series
b. dispersion
both (a) & (b)
A first order reaction requires two equal sized CSTR. The conversion is
more when they are connected in series.
In case of physical adsorption, the heat of adsorption is of the order of ____ kcal/kg.mole.
1000
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.
a. The unit of space velocity is (time)-1 .
b. The space velocity of 3 hr-1 means that three reactor volumes of feed at specified conditions are being fed into the reactor every hour.
c. The space velocity of 3 hr-1 means that one third reactor volume of feed at specified conditions are being fed into the reactor.
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 ?
0.95
The rate constant of a chemical reaction decreases by decreasing the
temperature
Reaction rate equation for the reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/448-153-1.png . If S at is present in large excess, what is the order of this reaction?
one
Rate of a gaseous phase reaction is given by, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/460-311-1.png . The unit of rate constant is
(atm)-1.(hr)-1
____ 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
For a reaction of the type, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/458-286-1.png , the rate of reaction (- rx) is given by
K1CV - K2CX
In a consecutive reaction system https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/446-134-1.png when E1 is much greater than E2, the yield of B increases with the
increase of temperature.
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.
The rate constant of a chemical reaction increases by 100 times when the temperature is increased from 400 °K to 500 °K. Assuming transition state theory is valid, the value of E/R is
9210°K
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.
The increase in the rate of reaction with temperature is due to
decrease in activation energy.
A catalyst loses its activity due to
a. loss in surface area of the active component.
b. agglomeration of metal particles caused by thermal sintering of the solid surface.
c. covering of the catalytic active sites by a foregin substance.
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
a. is independent of temperature.
b. varies with temperature.
c. depends on the nature of the reactants.
both (b) and (c).
For the irreversible elementary reactions in parallel viz https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/455-247-1.png , the rate of disappearance of ‘X’ is equal to
CA(K1+K2)
For an isothermal variable volume batch reactor, the following relation is applicable for a first order irreversible reaction.
CAo/(1+εAXA)(dXA/dt) = k
For a zero order chemical reaction, the
all (a), (b) and (c).
BET apparatus
a. measures the catalyst surface area directly.
b. operates at very high pressure.
c. is made entirely of stainless steel.
none of these.
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 catalysed chemical reaction, the effectiveness of solid catalyst depends upon the ____ adsorption.
chemical
Pick out the correct statement.
a. In catalytic reactions, the catalyst reacts with the reactants.
b. A catalyst initiates a chemical reaction.
c. A catalyst lowers the activation energy of the reacting molecules.
d. A catalyst can not be recovered chemi cally unchanged at the end of the chemical reaction.
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.
a. The vessel dispersion number (D/UL) for plug flow and mixed flow approaches zero and infinity respectively.
b. Space time in a flow reactor is a measure of its capacity and is equal to the residence time when the density of reaction mixture is constant.
c. Mixed reactor is always smaller than the plug flow reactor for all positive reaction orders for a particular duty.
d. In an ideal tubular flow reactor, mixing takes place in radial direction and there is no mixing in logitudinal direction.
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).
At a given value of E/R (ratio of activation energy and gas constant), the ratio of the rate constants at 500°K and 400°K is 2, if Arrhenious law is used. What will be this ratio, if transition state theory is used with the same value of E/R?
2.5
____ 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
The ratio of volume of mixed reactor to the volume of P.F.R. (for identical flow rate, feed composition and conversion) for zero order reaction is
1
Which of the following will favour the reverse reaction in a chemical equilibrium reaction ?
a. Increasing the concentration of one of the reactants.
b. Increasing the concentration of one or more of the products.
c. Removal of at least one of the products at regular interval.
Increasing the concentration of one or more of the products.
Conversion increases with increase in temperature in case of a an ____ reaction.
reversible endothermic
Effective diffusivity (DE) in a catalyst pellet is related to molecular diffusivity (DN) and Knudsen diffusivity (DK) as
1/DE = 1/DN + 1/DK
A photochemical reaction is ____ light.
initiated by
Pick out the wrong statement.
a. In a batch reactor, which is exclusively used for liquid phase reactions; temperature pressure and composition may vary with time.
b. In a semi-batch reactor, one reactant is charged batchwise, while the other reactant is fed continuously.
c. In a continuous flow reactor, uniform concentration can not be maintained throughout the vessel even in a well agitated system.
d. In a continuous flow reactor, both the reactants and the products flow out continuously.
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.
For a vapour phase catalytic reaction (A + B –> P) which follows the Ridel mechanism and the reaction step is rate controlling, the rate of reaction is given by (reaction rate is irreversible, product also absorbs).
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-472-1.png
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
For a series of reactions https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/473-457-1.png having k1 «_space;k2, the reaction system can be approximated as
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/476-478-1u.png
At a given temperature, K1, K2 and K3 are equilibrium constants for the following reactions 1, 2, 3 respectively.
CH4(g) + H2O(g) CO(g) + 3H2(g),
CO(g) + H2O(g) CO2(g) + H2(g)
CH4(g) + 2H2O(g) CO2(g) + 4H2(g)
Then K1, K2 and K3 are related as:
K3 = K1.K2
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
What is the Thiele modulus of the solid catalysed first order reaction, https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/448-154-1.png , if the pore diffusion offers negligible resistance to reaction ?
< 0.5
B.E.T. method can be used to determine the ____ of a porous catalyst.
surface area
Rate constant for a first order reaction does not depend upon reaction time, extent of reaction and the initial concentration of reactants ; but it is a function of reaction temperature. In a chemical reaction, the time required to reduce the concentration of reactant from 100 gm moles/litre to 50 gm moles/litre is same as that required to reduce it from 2 gm moles/litre to 1 gm mole/litre in the same volume. Then the order of this reaction is
1
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).
For a gaseous phase reaction, rate of reaction is equal to K. CA . CB. If the volume of the reactor is suddenly reduced to l/4th of its initial volume, then the rate of reaction compared to the original rate will be ____ times.
16
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.
The effect of increasing pressure on the gaseous equilibrium of the reaction 2X+3Y <–>3X+2Y indicates that
pressure has no effect.
If in the gaseous phase reaction, N2O4 <–> 2NO2, x is the part of N2O4 which dissociates, then the number of molecules at equilibrium will be
(1 + x)
A batch reactor is characterised 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.
a. increases
b. decreases
either (a) or (b); depends on the type of catalyst
Signal normally used to study non-ideal flow by stimulus response technique is ____ input.
a. pulse
b. step
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 PFR.
0.6
A high space velocity means that a given
a. reaction can be accomplished with small reactor.
b. conversion can be obtained with a high feed rate.
both (a) and (b).
In flow reactors, the performance equations interrelate the rate of reaction to the
all (a), (b) and (c).
