Chemical Reaction Engineering Flashcards
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 -> , 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
A first order reaction requires two equal sized CSTR. The conversion is
more when they are connected in series.
A reactor is generally termed as an autoclave, when it is a
high pressure batch 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.
The rate constant of a chemical reaction decreases by decreasing the
temperature
Reaction rate equation for the reaction, . If S at is present in large excess, what is the order of this reaction?
1
Rate of a gaseous phase reaction is given by, . The unit of rate constant is
(atm)-1.(hr)-1
‘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
In an exothermic chemical reaction, the reactants compared to the products have
more energy
A batch reactor is suitable for
liquid phase reactions.
In a consecutive reaction system 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.
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.
‘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
For the irreversible elementary reactions in parallel viz , the rate of disappearance of ‘X’ is equal to
CA(K1+K2)
BET apparatus
none of these.
For an isothermal variable volume batch reactor, the following relation is applicable for a first order irreversible reaction.
For a solid catalysed 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.
Pick out the wrong statement.
Mixed reactor is always smaller than the plug flow reactor for all positive reaction orders for a particular duty.
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
__________ is the controlling step in a highly temperature sensitive fluid-solid non-catalytic reaction.
Chemical reaction
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
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
Conversion increases with increase in temperature in case of a an __________ reaction.
reversible endothermic
A photochemical reaction is __________ light.
initiated by
‘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
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
Which of the following is an independent variable for a batch tank reactor with uniform concentration and temperature ?
Time
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
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.
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.
Rate determining step in a reaction consisting of a number of steps in series is the __________ step.
slowest
A catalyst in a chemical reaction __________ free energy change in the reaction.
either (a) or (b); depends on the type of catalyst
When all the limiting reactant is consumed in the reaction, the operational yield __________ the relative yield.
equals
The catalyst in a second order reversible reaction increases the rate of the forward reaction
and backward reaction equally.
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.
0.60
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
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
∞
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
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
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.
To maximise the formation of R in the simultaneous reaction
A + B -> R , rR = 2CA0.5.CB2
A + B -> S , rS = 1.5 CA . CB
We should have
low CA, high CB
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
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 value of steric factor ‘P’ in the equation k = PZeE/RT usually ranges from
l.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
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 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
__________ 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
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
Pick out the wrong statement.
When the reaction rate is independent of temperature, the reaction is said to be of zero order.
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
In a semi-batch reactor,
velocity of reaction can be controlled.
In a chemical reaction , 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
In the gaseous phase ammonia formation reaction (N2 + 3H2 2NH3), the value of the equilibrium constant depends on the
temperature.
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
For an ideal gas mixture undergoing a reversible gaseous phase chemical reaction, the equilibrium constant
increases with pressure.
A batch reactor is
suitable for liquid phase reactions involving small production rate.
Pick the WRONG design guideline for a reactor in which the reactions, A -> R (desired) and A -> S (undesired) are to take place. The ratio of the reaction rates is .
avoid recycle, when a > b.
An elementary liquid phase decomposition reaction is to be carried out in a CSTR. The design equation is
kτ = XA/(1 - XA)
The order of the reaction, , is
0
The first order gas phase reaction is conducted isothermally in batch mode. The rate of change of conversion with time is given by
For the reaction , the rate of formation of Z is 0.2 gm mole/litre.hr. what is the rate of disappearance of X in gm mole/litre. hr ?
0.4
Volume change for unimolecular type first order reaction , increases __________ with time.
exponentially
.
Decomposition rate of a liquid ‘X’ which decomposes as per the reaction is given by
(K1 + K2)CX
For a __________ order chemical reaction, , the half life period is independent of the initial concentration of the reactant A.
1
A second order liquid phase reaction, A B, is carried out in a mixed flow reactor operated in semi batch mode (no exit stream). The reactant A at concentration CAF is fed to the reactor at a volumetric flow rate of F. The volume of the reacting mixture is V and the density of the liquid mixture is constant. The mass balance for A is
For a __________ order chemical reaction, , the fractional conversion of reactant ‘A’ is proportional to time.
zero
