CRE Flashcards by Franklin Yaun

Which of the following will give maximum gas conversion ?

Semi-fluidised bed reactor.

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The dimensions of rate constant for reaction 3A–>B are (l/gm mole)/min. Therefore the reaction order is

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

The rate of the reaction, X Y, quadruples when the concentration of ‘X’ is doubled. The rate expression for the reaction is, r = K Cxn, the value of ‘n’ in this case will be

The knowledge of initial concentration and rate constant is necessary to determine the half life time of a reaction of __________ order.

2 (Second)

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What is the order of a chemical reaction, A+2B–>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

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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.

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The most unsuitable reactor for carrying out reactions in which high reactant concentration favours high yields is

Which of the following is the most suitable for isothermal operation ?

backmix reactor

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A reactor is generally termed as an autoclave, when it is a

high pressure batch reactor.

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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%

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Which of the following is the most suitable for very high pressure gas phase reaction ?

Tubular flow reactor

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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

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The increase in the rate of reaction with temperature is due to

decrease in activation energy.

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Radioactive decay follows __________ order kinetics.

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

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 CA^n, then what is the value of n for this reaction ?

What is the order of a chemical reaction whose rate is determined by the variation of one concentration term only ?

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

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

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 ?

first

1 (First)

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

decreases the energy barrier for reaction.

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When the density of the reaction mixture is constant in a chemical reaction, the ratio of the mean residence time to space time is

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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

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__________ is the controlling step in a highly temperature sensitive fluid-solid non-catalytic 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

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The rate constant of a first order reaction depends on the

temperature

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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

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

Which one is the rate controlling step in a solid-gas non-catalytic reaction occurring at very high temperature?

film

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The units of frequency factor in Arhenious equation

are the same as those of the rate constant.

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

auto catalytic

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

stirred tank

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B.E.T. method can be used to determine the __________ of a porous catalyst.

surface area

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

Time

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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.

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In a reversible chemical reaction having two reactants in equilibrium, if the concentration of the reactants are doubled, then the equilibrium constant will The equilibrium constant of a catalytic chemical reaction __________ due to the presence of a catalyst. remain the same

remain the same/unaffected

The rate constant of a chemical reaction increases by increasing the temperature

temperature

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)

(1 + x)

When a catalyst increases the rate of forward reaction, the value of rate constant increases

increases

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

512

When all the limiting reactant is consumed in the reaction, the operational yield __________ the relative yield. equals

equals

The half life period of a first order reaction is independent on initial concentration of the reactants.

independent on initial concentration of the reactants.

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

0.60

The fractional volume change between no conversion and complete conversion, for the isothermal gas phase reaction, 2A-->R, is -0.5

-0.5

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.

τ = θ , for an isothermic tubular reactor in which the density of the process fluid is constant.

A plug-flow reactor is characterised by presence of lateral mixing.

presence of lateral mixing.

Which of the following curves shows the effect of temperature on the extent of gas-solid adsorption at a given pressure ? Adsorption isobar

Adsorption isobar

In chamber process of sulphuric acid manufacture in industry, the gas phase oxidation of SO2 to SO3 is accomplished by a __________ reaction. __________ catalytic reaction is involved in the thermal cracking of gas oil. catalytic homogenous

catalytic homogenous

Fluid flow in a real packed bed can be approximated as __________ model. dispersion

dispersion

If the rate of a chemical reaction becomes slower at a given temperature, then the free energy of activation is higher.

free energy of activation is higher.

For a zero order reaction, the concentration of product increases with the increase of reaction time.

increase of reaction time.

Effectiveness factor of a catalyst pellet is a measure of the __________ resistance. pore diffusion

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

same

The reaction in which the rate equation corresponds to a stoichiometric equation, is called a/an __________ reaction. elementary

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 What is the order of a chemical reaction in which doubling the initial concentration of the reactants doubles the half life time of the reaction ? For a __________ order reaction, the units of rate constant and rate of reaction are the same. For a __________ order chemical reaction, , the fractional conversion of reactant 'A' is proportional to time. Rate of a chemical reaction is independent of the concentration of the reactants for a __________ reaction. 0

0 (zero)

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

10°C

A backmix reactor is same as ideal stirred tank reactor.

is same as ideal stirred tank reactor.

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

600

In a semi-batch reactor, velocity of reaction can be controlled.

velocity of reaction can be controlled.

Which of the following is a controlling factor in very fast heterogeneous reaction ? Heat and mass transfer effects

Heat and mass transfer effects

In a chemical reaction X+Y+Z --> P, 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? If the time required for half change is inversely proportional to the square of initial concentration and the velocity depends on the units in which the concentration term is expressed, then the order of reaction is The value of 'n' for a chemical reaction A-->B, whose reaction rate is CA^n, will be __________ if the rate of the reaction increases by a factor of 8, when the concentration of is doubled. Third order

3 (Third)

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

5/3 kW

For an ideal gas mixture undergoing a reversible gaseous phase chemical reaction, the equilibrium constant increases with pressure.

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.

the combination reaction will be exothermic, while the dissociation reaction will be endothermic.

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

Second order consecutive irreversible reactions A-->B --> C 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)? 1/4

1/4

There is no correspondence between stoichiometry and the rate equation in case of a/an __________ reaction. non-elementary

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.

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

Moving bed reactor

An isothermal aqueous phase reversible reaction, P-->R, is to be carried out in a mixed flow reactor. The reaction rate in k.mole/m3 .h is given by, r = 0.5CP - 0.125CR. A stream containing only P enters the reactor. The residence time required (in hours) for 40% conversion of P is 1.60

1.60

What is the unit of the rate constant in a chemical reaction in which 10% of the reactant decomposes in one hour, 20% in two hours, 30% in three hours and so on ? Litre/mole.second

Litre/mole.second

The most suitable reactor for carrying out an auto-thermal reaction is a CSTR

CSTR

With increase in temperature, the equilibrium __________ rises in case of endothermic reaction. conversion

conversion

Enzymes (a protein) are catalysts found in organisms. Its efficiency of catalysing a reaction is due to its capacity to lower the activation energy of the reaction. The enzyme ptyalin used for food digestion is present in saliva

saliva

In the converter of the contact process for the manufacture of H2SO4 the equilibrium conversion of SO2 __________ (A) __________ with increase in temperature and __________ (B) __________ with increase in the mole ratio of SO2 to air. (A) decreases (B) increases

(A) decreases (B) increases

During manufacture of H2SO4, the oxidation of SO2 to SO3 by oxygen is an en-dothermic reaction. The yield of SO3 will be maximised, if the temperature is reduced and pressure is increased.

temperature is reduced and pressure is increased.

Carrier in a catalyst increases its surface area

surface area

When the reaction occurs in the diffusion controlled region, the apparent activation energy as measured is only __________ the true value. half

half

An isothermal irreversible reaction is being carried out in an ideal tubular flow reactor. The conversion in this case will __________ with decrease in space time. decrease

decrease

Kinetics of a solid catalysed reaction can best be studied in a __________ reactor. mixed

mixed

Which of the following is an autocatalytic reaction ? Microbial fermentation reaction

Microbial fermentation reaction

Holding time for flow reactors is __________ the space time, for constant fluid density equal to

equal to

Oil is hydrogenated using nickel catalyst in a __________ reactor. Vegetable oils are hydrogenated in a __________ reactor. slurry

slurry

The performance equations for constant density systems are identical for P.F.R. and batch reactor.

P.F.R. and batch reactor.

In the fluid catalytic cracker (FCC), the cracking reaction is __________ (A) and the regeneration is___(B) __________ (A) endothermic (B) exothermic

(A) endothermic (B) exothermic

An irreversible first order reaction is being carried out in a CSTR and PFR of same volume. The liquid flow rates are same. The relative conversion will be more in PFR than in CSTR.

be more in PFR than in CSTR.

When a high liquid hold up is required in a reactor for gas liquid reaction, use __________ coloumn. bubble

bubble

Higher free energy of activation of a chemical reaction (at a given temperature) implies slower rate of reaction.

slower rate of reaction.

The dispersion number of perfect mixed flow is ∞

∞

An irreversible aqueous phase reaction, A + B-->P, is carried out in an adiabatic mixed flow reactor. A feed containing 4kmole/m3 of each A and B enters the reactor at 8m3 /hr. If the temperature of the exit stream is never to exceed 390 K, what is the maximum inlet feed temperature allowed? Data: Heat of reaction = - 50 kJ/mole Density of the reacting mixture = 1000kg/m3 Specific heat of reacting mixture = 2kJ/kg.K The above data can be assumed to be independent of temperature and composition. 290

290

Volume change for A--> 4R unimolecular type first order reaction , increases __________ with time.

exponentially

Half life period of decomposition of a liquid 'A' by irreversible first order reaction is 12 minutes. The time required for 75% conversion of 'A' is __________ minutes. 24

With increase in the space time of an irreversible isothermal reaction being carried out in a P.F. reactor, the conversion will increase

increase

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

diffusion through ash layer

If ΔG (free energy change) for a chemical reaction is very large and negative, then the reaction is very much feasible.

very much feasible.

In a zero order reaction, reactants concentration does not change with time and the time for half change is half the time taken for completion of the reaction.

time for half change is half the time taken for completion of the reaction.

The minimum energy required to allow a chemical reaction to proceed is termed as the 'threshold energy '. Chemical reaction with low activation energy are insensitive to temperature changes.

insensitive to temperature changes.

For an ideal plug flow reactor, the value of Peclet number is 0

An endothermic aqueous phase first order irreversible reaction is carried out in an adiabatic plug flow reactor. The rate of reaction is maximum at the inlet of the reactor.

is maximum at the inlet of the reactor.

An endothermic second order reaction is carried out in an adiabatic plug flow reactor. The rate of heat generation is maximum at the inlet of the reactor.

maximum at the inlet of the reactor.

The size of plug flow reactor (PFR) for all positive reaction orders and for any given duty, is __________ that of mixed reactor. smaller than

smaller than

When an exothermic reversible reaction is conducted adiabatically, the rate of reaction passes through a maximum.

passes through a maximum.

In a semi-batch reactor velocity of reaction can be controlled.

velocity of reaction can be controlled.

The ratio of moles of a reactant converted into the desired product to that converted into unwanted product is called selectivity

selectivity

The response curve for a step input signal from a reactor is called C-curve. The variance of C-curve in a 'tanks in series model' comprising of 'm' tanks is equal to 1/m

1/m

The eddy diffusivity for a liquid in plug flow must be 0

For the same residence time, which one will give the maximum conversion ? Single tubular flow reactor (v = 5 litres).

Single tubular flow reactor (v = 5 litres).

For the reversible reaction A=2B, if the equilibrium constant K is 0.05 mole/litre; starting from initially 2 moles of A and zero moles of B, how many moles will be formed at equilibrium ? 0.338

0.338

For identical flow rate and feed composition, X plug flow reactors (PER) in series with a total volume V gives the same conversion as single PFR of volume V

PFR of volume V

Pure A in gas phase enters a reactor 50% of this A is converted to B through the reaction, A-->3B. Mole fraction of A in the exit stream is 1/3

1/3

The heat of reaction is independent of the mechanism of reaction.

is independent of the mechanism of reaction.

Which of the following does not produce a change in the value of rate constant of a reaction ? Concentration and catalyst

Concentration and catalyst

With increase in temperature, the equilibrium conversion of a reversible exothermic reaction decreases

decreases

As the chemical reaction proceeds, the rate of reaction decreases.

decreases.

In a first order reaction, the time required to reduce the concentration of reactant from 1 mole/litre to 0.5 mole/litre will be __________ that required to reduce it from 10 moles/litre to 5 moles/litre in the same volume. same as

same as

Knudsen diffusion is directly proportional to sqrt T

sqrt T

Fractional conversion __________ for an exothermic reversible chemical reaction, when the temperature is maximum. decreases

decreases

A pulse tracer is introduced in an ideal CSTR (with a mean residence time ι) at time, t = 0. The time taken for the exit concentration of the tracer to reach half of its initial value will be 2τ

2τ

Promoter. increases the number of active centres by increasing the unevenness of catalyst surface and by creating discontinuities in the crystals.

increases the number of active centres by increasing the unevenness of catalyst surface and by creating discontinuities in the crystals.

If 'n' is the order of reaction, then unit of rate constant is 1/(time)(concentration)n - 1

1/(time)(concentration)n - 1

The use of space time is preferred over the mean residence time in the design of a/an ideal tubular-flow reactor

ideal tubular-flow reactor

The fractional volume change of the system for the isothermal gas phase reaction, A-->3B , between no conversion and complete conversion is 2

Autocatalytic reactions are best carried out in a recycle reactor

recycle reactor

The gas phase reaction 2A -->B is carried out in an isothermal plug flow reactor. The feed consists of 80 mole % A and 20 mole % inerts. If the conversion of A at the reactor exit is 50%, then CA/CA0 at the outlet of the reactor is 5/8

5/8

The reaction rate almost gets doubled for 10°C rise in temperature. This is due to the fact that the fraction of molecules having threshold energy increases.

fraction of molecules having threshold energy increases.

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

15, 10, 5

The molecularity and the order of reaction respectively, for the hydrolysis of methyl acetate in presence of acids are 2 & 1

2 & 1

The irreversible reaction is a special case of reversible reaction, if the reactant concentration at equilibrium condition is zero.

reactant concentration at equilibrium condition is zero.

A pollutant P degrades according to first order kinetics. An aqueous stream containing P at 2 kmole/m3 and volumetric flow rate 1m3 /h requires a mixed flow reactor of volume V to bring down the pollutant level to 0.5 kmole/m3 . The inlet concentration of the pollutant is now doubled and the volumetric flow rate is tripled. If the pollutant level is to be brought down to the same level of 0.5 kmole/m3 , the volume of the mixed flow reactor should be increased by a factor of 7

Exothermic reactions are best carried out in CSTR followed by a plug flow reactor.

CSTR followed by a plug flow reactor.

Reactions with high activation energy are very temperature sensitive

very temperature sensitive

In case of a/an __________ chemical reaction, conversion increases with the rise in temperature. reversible endothermic

reversible endothermic

What is the dispersion number for a plug flow reactor ? 0

The rate of reaction of a/an __________ reaction is not affected by temperature rise. photochemical

photochemical

The catalytic converter for conversion of SO2 to SO3 by contact process should have a feed with SO2 content between 7-10%

7-10%

A gaseous reactant is introduced in a mixed reactor of 3 litres volume at the rate of 1 litre/second. The space time is __________ seconds. 3

Backmixing is most predominant in a single CSTR.

a single CSTR.

Rate constant 'k' and absolute temperature 'T' are related by collision theory (for bimolecular) as k ∝ sqrt T

k ∝ sqrt T

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

What is the dispersion number for a CSTR? ∞

∞

Bulk diffusion in catalyst pore __________ with increase in pressure. decreases

decreases

Toluene and hydrogen are fed to a reactor in a molar ratio 1:5.80% of the toluene gets converted and the selectivity of benzene(defined as moles of benzene formed/moles of toluene converted) is 90%. The fractional conversion of hydrogen is 0.144

0.144

The enzyme which can catalyse the conversion of glucose to ethyl alcohol is zymase

zymase

A second order reaction of the form A + B C is called a pseudo-first order reaction, when CB0 ≥ CB0

CB0 ≥ CB0

Inversion of cane sugar is an example of bimolecular reaction with first order.

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

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

proportional to

An example of autothermal reactor operation is ethylene oxidation

ethylene oxidation

__________ resistance is not involved in the combustion of a carbon particle. Ash

Ash

For a packed bed reactor; the presence of a long tail in the residence time distribution curve is an indication of dead zone

dead zone

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.

catalyst size is reduced or the catalyst diffusivity is increased.

CRE Flashcards

(143 cards)