Reaction Engineering (Set 2) Flashcards
Concepts necessary for reactor design, operation, and maintenance.
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.
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
The exit age distribution of a fluid leaving a vessel (denoted by E) is used to study the extent of non-ideal flow in the vessel. The value of https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/467-387-1.png is
1
A plug-flow reactor is characterised by
presence of lateral mixing.
Three plug flow reactors (PFR’s) of 4, 5 & 6 m3 volumes are arranged in two branches as shown below in the figure. https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/468-389-1.png If the total feed rate is 300 tons/hr, then for the same conversion in each branch, the feed rate through branch II should be ____ tons/hr.
100
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
Fluid flow in a real packed bed can be approximated as ____ model.
dispersion
For series reaction, the relative yield
both (a) and (c) hold good.
The ‘E’ curve for a non-ideal reactor defines the fraction of fluid having age between t and t + dt
at the outlet
To maximise the formation of R in the simultaneous reaction
A + B –> R , rR = 2CA^0.5.CB^2
A + B –> S , rS = 1.5 CA . CB
We should have
low CA, high CB
A reaction which is catalysed by an acid is also catalysed by any substance, which has a tendency to
lose a proton.
A stirred tank reactor compared to tubular-flow reactor provides
a. more uniform operating conditions.
b. permits operation at the optimum temperature for a long reaction time.
c. higher overall selectivity for a first order consecutive reaction.
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.
The conversion XA and residence time data are collected for zero order liquid phase reaction in a stirred tank reactor. Which of the following will be a straight line ?
XA Vs . τ
The rate of the reaction, X–> Y, quadruples when the concentration of ‘X’ is doubled. The rate expression for the reaction is, r = K Cx^n, the value of ‘n’ in this case will be
2
The value of steric factor ‘P’ in the equation k = PZe^E/RT usually ranges from
1.0 to 10^-8
For a zero order reaction, the concentration of product increases with the
increase of reaction time.
Pick out the wrong statement.
A batch reactor can not be used to study the kinetics of catalytic reaction.
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)
Given,
3H2 + CO = CH4 + H2O, KP = 101.84 and,
4H2 + CO2 = CH4 + 2H2O, KP = 101.17
the KP for the reaction CO + H2O = CO2 + H2 is
10^0.67
Differential method for analysing 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
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
A first order gaseous phase reaction is catalysed by a non-porous solid. The kinetic rate constant and the external mass transfer co-efficients are k and kg respectively. The effective rate constant (keff) is given by
1/keff = 1/k + 1/kg
Arrhenious equation represents graphically the variation between the ____ and temperature.
rate constant
____ catalytic reaction is involved in the thermal cracking of gas oil.
Homogeneous
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
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 batch adiabatic reactor at an initial temperature of 373°K is being used for the reaction, A–>B. Assume the heat of reaction is - 1kJ/mole at 373°K and heat capacity of both A and B to be constant and equal to 50J/mole.K. The temperature rise after a conversion of 0.5 will be
10°C
If CA is the quantity of reactants initially present, the quantity left after ‘n’ half periods will be equal to
(1/2)^n.CA
A photochemical reaction is
initiated by light.
The rate controlling step for the heterogeneous irreversible catalytic reaction A(g) + B(g)–> C(g) is the surface reaction of absorbed A with absorbed B to give adsorbed C. The rate expression for this reaction can then be written as (where, KA, KB and KC are the equilibrium constants and is the rate constant of the rate controlling step.)
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/470-420-4.png
The optimum performance for reactors operating in parallel is obtained when the feed stream is distributed in such a way, that the
space time for each parallel line is same.
A catalyst is said to be a negative catalyst, ifit
retards the rate of reaction.
For the non catalytic reaction of particles with surrounding fluid, the same needed to achive the same fractional conversion for particles of different unchanging sizes is proportional to the particle diameter, when the ____ is the controlling resistance.
chemical reaction
Pure ethanol vapor is fed to a reactor packed with alumina catalyst, at the rate of 100 kmole / hr. The reactor products comprise: ethylene :95 kmole / hr, water vapour: 97.5 k mole / hr and diethyl ether :2.5 kmole/hr. The reactions occuring can be represented by:
C2H5OH C2H4 + H2O
2C2H5OH C2H5 - O - C2H5 + H2O
The percent conversion of ethanol in the reactor is
100
The conversion for a second order, irreversible reaction (constant volume), https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-469-1.png , in batch mode is given by
https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/475-469-3.png
Pick out the wrong statement.
When the reaction rate is independent of temperature, the reaction is said to be of zero order.
A backmix reactor
is same as ideal stirred tank reactor.
Rate of a chemical reaction is not influenced by the
number of molecules of reactants taking part in a reaction
Pick out the wrong statement:
The residence time for all the elements of fluid in case of a P.F.R. need not be same.
The reaction A B is conducted in an adiabatic plug flow reactor (PFR). Pure A at a concentration of 2 kmol/m3 is fed to the reactor at the rate of 0.01 m3 /s and at a temperature of 500 K. If the exit conversion is 20%, then the exit temperature (in k)is (Data: Heat of reaction at 298 K = - 50000 kJ/ kmole of A reacted Heat capacities CPA = CPB = 100kJ/kmole. K (may be assumed to be independent of temperature))
600
Which of the following is not a theory of homogeneous reaction?
None of these
A first order homogeneous reaction of the type X Y Z (consecutive reaction) is carried out in a CSTR. Which of the following curves respectively show the variation of the concentration of X, Y and Z with time? https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/446-129-1.png
III, II, I
In a semi-batch reactor,
velocity of reaction can be controlled.
Most important characteristics of gas-liquid reactors are the
both (a) and (b)
Which of the following is a controlling factor in very fast heterogeneous reaction?
Heat and mass transfer effects
Enzymes are destroyed, when the
temperature is very high,
For an autocatalytic reactor, the suitable reactor set up is
CSTR followed by P.F. reactor.
Ionic reactions occur in
solutions
Sometimes, batch process is preferred over continuous process, when the product
both (a) & (b).
In a chemical reaction https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/454-240-1.png , it is observed that the
(i) rate of formation of ‘P’ is doubled on doubling the concentration of ‘X’.
(ii) rate of formation of ‘P’ is quadrupled on doubling the concentration of ‘Y’.
(iii) doubling the concentration of ‘Z’ does not affect the rate of formation of ‘P’.
What is the order of the above chemical reaction?
Third order
The half life period of a first order reaction is given by (where, K = rate constant. )
0.693/K
Half life period of a chemical reaction is
the time required to reduce the concentration of the reacting substance to half its initial value.
In the gaseous phase ammonia formation reaction (N2 + 3H2<–>2NH3), the value of the equilibrium constant depends on the
temperature.
Transition state theory relates the above quantities as
k ∝ T.e^E/RT
Photochemical reaction rate does not depend significantly on temperature, because
the energy of reacting molecules exceeds the activation energy by absorption of light.
A CSTR is to be designed in which an exothermic liquid phase first order reaction of the type, A–>R, is taking place. The reactor is to be provided with a jacket in which coolant is flowing. Following data is given: CA0= 5 kmole/m3 ; XA = 0.5; Feed temperature = reactor temperature = 40°C. Rate constant at 40°C = 1 min-1 ; (ΔH) = - 40kJ/mole; ρ = 1000kg/m3 CP = 4 J/gm.°C ; q = 10-3 m3/min (ρ and CP are same for the reactant and product streams). The amount of heat to be removed is
5/3 kW
According to the ‘law of mass action’, the rate of reaction is directly proportional to the
molar concentration of the reactants.
In a chemical reaction, ____ are conserved.
both(b) & (c)
For an ideal gas mixture undergoing a reversible gaseous phase chemical reaction, the equilibrium constant
increases with pressure.
In the reversible reaction of the type, A + B <–> AB, in general
the combination reaction will be exothermic, while the dissociation reaction will be endothermic.
A batch reactor is
suitable for liquid phase reactions involving small production rate.
For a first order reaction carried out in a plug flow reactor, the space time is
1/K ln Co/C
For an isothermal second order aqueous phase reaction, A –> B, the ratio of the time required for 90% conversion to the time required for 45% conversion is
11
A chemical reaction is of zero order, when the reaction rate is (where, CA = concentration of reactant)
none of these.
Second order consecutive irreversible reactions https://www.indiabix.com/_files/images/chemical-engineering/chemical-reaction-engineering/473-457-1.png were carried out in a constant volume isothermal batch reactor with different initial feed compositions. Reactor temperature was same in all the cases. In experiments where the ratio of concentration of B to that of A in the initial feed was less than 0.5, the concentration of B increased first, reached a maximum and then declined with time. However, for all experiments where this concentration ratio was 0.5 or above, concentration of B decreased monotonically with time right from the beginning. What is the ratio of the two rate constants (k1/k2)?
45295
Pick out the wrong statement.
Enzymes help in increasing the activation energy of the reaction.
There is no correspondence between stoichiometry and the rate equation in case of a/an ____ reaction.
non-elementary
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?
Inner catalyst core of radius R/8 does not participate in reaction.
Which of the following is used for calcination of limestone and dolomite in industrial practice ?
Moving bed reactor
An imbalanced chemical reaction equation is against the law of
conservation of mass
For the chemical reaction P Q, it is found that the rate of reaction doubles as the concentration of ‘P’ is doubled. If the reaction rate is proportional to Cpn, then what is the value of ‘n’ for this chemical reaction ?
1
Which of the following is a characteristic of an ideal plug flow reactor ?
Flat velocity profile
Velocity of a reaction depends upon the
all (a), (b) and (c).
Threshold energy in a reaction is equal to the
sum of (a) & (b)
