Practice Chemical Reaction Engineering Multiple Choice Questions with Answers Quiz-17

Q.1.

The rate constant of a chemical reaction increases bytimes when the temperature is increased from°K to°K. Assuming transition state theory is valid, the value of E/R is

8987°K
9210°K
8764°K
8621°K

Q.2.

A reaction which is catalysed by an acid is also catalysed by any substance, which has a tendency to

lose a proton.
gain a proton.
lose an electron
none of these.

Q.3.

A catalyst loses its activity due to

loss in surface area of the active component.
agglomeration of metal particles caused by thermal sintering of the solid surface.
covering of the catalytic active sites by a foregin substance.
all (a), (b) and (c).

Q.4.

'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.

first
second
third
any

Q.5.

With decrease in temperature, the equilibrium conversion of a reversible endother-mic reaction

decreases
increases
remains unaffected
increases linearly with temperature

Q.6.

Velocity of a reaction depends upon the

nature of the reactants.
concentration of the reactants.
temperature at which the reaction is carried.
all (a), (b) and (c).

Q.7.

Pick out the correct statement.

In catalytic reactions, the catalyst reacts with the reactants.
A catalyst initiates a chemical reaction.
A catalyst lowers the activation energy of the reacting molecules.
A catalyst can not be recovered chemi cally unchanged at the end of the chemical reaction.

Q.8.

Pick out the wrong statement.

The vessel dispersion number (D/UL) for plug flow and mixed flow approaches zero and infinity respectively.
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.
Mixed reactor is always smaller than the plug flow reactor for all positive reaction orders for a particular duty.
In an ideal tubular flow reactor, mixing takes place in radial direction and there is no mixing in logitudinal direction.

Q.9.

For a zero order chemical reaction, the

half life period is directly proportion to the initial concentration of the reac-tants.
plot of products concentration with time is a straight line through the origin.
products concentration increases linerarly with time.
all (a), (b) and (c).

Q.10.

__________ explains the mechanism of catalysis.

Activated complex theory
Collision theory
Thermodynamics
None of these

Q.11.

A stirred tank reactor compared to tubular-flow reactor provides

more uniform operating conditions.
permits operation at the optimum temperature for a long reaction time.
higher overall selectivity for a first order consecutive reaction.
all (a), (b) and (c)

Q.12.

Catalyst carriers

have very high selectivity.
increase the activity of a catalyst.
provide large surface area with a small amount of active material.
inhibit catalyst poisoning.

Q.13.

Rate of a chemical reaction is not influenced by the

catalyst
temperature
reactants concentration
number of molecules of reactants taking part in a reaction

Q.14.

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.15.

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 fromgm moles/litre togm 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

0
1
2
3

Q.16.

The equilibrium constant of a catalytic chemical reaction __________ due to the presence of a catalyst.

increases
decreases
remains unaffected
unpredictable from the data

Q.17.

Threshold energy in a reaction is equal to the

activation energy
normal energy of reactants
sum of (a) & (b)
neither (a) nor (b)

Q.18.

__________ is the response curve for a step input signal from a reactor.

S-curve
C-curve
I-curve
none of these

Q.19.

'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

pressure
temperature
both (a) & (b)
neither (a) nor (b)

Q.20.

A batch reactor is suitable for

achieving cent percent conversion of reactants into products.
large scale gaseous phase reactions.
liquid phase reactions.
obtaining uniform polymerisation products in highly exothermic reactions.

Q.21.

Specific rate constant for a second order reaction

is independent of temperature.
varies with temperature.
depends on the nature of the reactants.
both (b) and (c).

Q.22.

In an exothermic chemical reaction, the reactants compared to the products have

higher temperature
more energy
less energy
same energy.

Q.23.

The rate constant of a first order reaction depends on the

concentration of the reactant.
temperature.
concentration of the product.
time.

Q.24.

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 formto 100°C.

256
512
112
612

Q.25.

Pick out the correct statement

Reactions with high activation energies are very temperature sensitive.
Chemical equilibrium is a static state.
A photochemical reaction is catalysed by light.
A chemical reaction occurs when the energy of the reacting molecule is less than the activation energy of the reaction.

Q.26.

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.27.

The reason why a catalyst increases the rate of reaction is that, it

decreases the energy barrier for reaction.
increases the activation energy.
decreases the molecular collision diameter.
none of these.

Q.28.

BET apparatus

measures the catalyst surface area directly.
operates at very high pressure.
is made entirely of stainless steel.
none of these.

Q.29.

From among the following, choose one which is not an exothermic process.

Methanol synthesis
Catalytic cracking
Ammonia synthesis
Oxidation of sulphur

Q.30.

A high space velocity means that a given

reaction can be accomplished with small reactor.
conversion can be obtained with a high feed rate.
both (a) and (b).
none of these.

Q.31.

In case of __________ reactions, the reaction rate does not decrease appreciably as the reaction proceeds.

catalytic
parallel
series
auto catalytic

Q.32.

For nearly isothermal operation involving large reaction time in a liquid-phase reaction, the most suitable reactor is a __________ reactor.

stirred tank
tubular flow
batch
fixed bed

Q.33.

Pick out the correct statement

Reactions with high activation energies are very temperature sensitive.
Chemical equilibrium is a static state.
A photochemical reaction is catalysed by light.
A chemical reaction occurs when the energy of the reacting molecule is less than the activation energy of the reaction.

Q.34.

The reason why a catalyst increases the rate of reaction is that, it

decreases the energy barrier for reaction.
increases the activation energy.
decreases the molecular collision diameter.
none of these.

Q.35.

Which of the following is an independent variable for a batch tank reactor with uniform concentration and temperature ?

Time
Useful volume of the tank
Diameter of the reactor
None of these

Q.36.

The rate constant of a chemical reaction increases by increasing the

temperature
pressure
reactant's concentration
none of these

Q.37.

The catalytic activity of enzymes is due to their capacity to lower the __________ energy.

activation
potential
kinetic
none of these

Q.38.

A chemical reaction is of zero order, when the reaction rate is (where, C_A = concentration of reactant)

∝ C_A.
∝ 1/C_A.
independent of temperature.
none of these.

Q.39.

A high space velocity means that a given

reaction can be accomplished with small reactor.
conversion can be obtained with a high feed rate.
both (a) and (b).
none of these.

Q.40.

For nearly isothermal operation involving large reaction time in a liquid-phase reaction, the most suitable reactor is a __________ reactor.

stirred tank
tubular flow
batch
fixed bed

Q.41.

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.42.

A chemical reaction is of zero order, when the reaction rate is (where, C_A = concentration of reactant)

∝ C_A.
∝ 1/C_A.
independent of temperature.
none of these.

Q.43.

A reaction in which one of the products of reaction acts as a catalyst is called a/an __________ reaction.

catalytic
autocatalytic
photochemical
none of these

Q.44.

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

∞
0
1
> 1

Q.45.

If a solid-gas non-catalytic reaction occurs at very high temperature, the rate controlling step is the __________ diffusion.

film
ash layer
pore
none of these

Q.46.

A photochemical reaction is __________ light.

initiated by
accompanied with emission of
catalysed by
used to convert heat energy into

Q.47.

Pick out the wrong statement.

In a batch reactor, which is exclusively used for liquid phase reactions; temperature pressure and composition may vary with time.
In a semi-batch reactor, one reactant is charged batchwise, while the other reactant is fed continuously.
In a continuous flow reactor, uniform concentration can not be maintained throughout the vessel even in a well agitated system.
In a continuous flow reactor, both the reactants and the products flow out continuously.

Q.48.

A catalyst in a chemical reaction __________ free energy change in the reaction.

increases
decreases
either (a) or (b); depends on the type of catalyst
neither (a) nor (b).

Q.49.

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

0
1
2
3

Q.50.

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.

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