# Chemical Reaction Engineering

CRE

1. The dimension of the rate constant k for an n-th order reaction is
(a) (time)-(concentration)-1
(b) (time)1-n (concentration)-1
(c) (time)-1 (concentration)1-n
(d) (time)-1 (concentration)-n

3. Reactions in which the rate equation corresponds to a stoichiometric equation are called
(a) elementary reactions
(b) nonelementary reactions
(c) heterogeneous reactions
(d) none of the above

4. Rate of a reaction depends on
(a) temperature only
(b) pressure only
(c) composition only
(d) temperature and composition
5. The rate expression for the reaction between Hand Brto produce HBR (H+ Br= HBR) is given by The reaction is
(a) stochiometric
(b) fundamental
(c) elementary
(d) non-elementary

7. For an elementary reaction
(a) - r= r= k1CA
(b) - r= r= k1C
(c) - r= r= k1
(d) - r= r= k1CA1.5

8. Consider the rate expression
(a) 0.7              (b) 0.3             (c) 0.4             (d) 1.0

14. characterized by conducted in a batch reactor is
(a) linear
(c) parabolic

(b) exponential
(d) none of these

9. For a zero order reaction the fractional conversion of the reactant is
(a) directly proportional to the initial concentration
(b) inversely proportional to the initial concentration
(c) independent of the initial concentration
(d) directly proportional to the square root of the initial concentration

10. For a first order reaction the plot of ln (CA/CAO ) vs. time
(a) is linear and passes through the origin
(b) is exponential and passes through the origin
(c) is linear but does not pass through the origin
(d) is exponential but does not pass through the origin

11. For a zero order reaction the plot of fractional conversion vs. time is
(a) a straight line parallel to the time axis (X-axis)
(b) a straight line passing through the origin
(c) a straight line which does not pass through the origin and is not parallel to the time axis (d) none of these

12. For an auto catalytic reaction A + R ® R + R, the plot of fractional conversion of A vs. time is
(a) a straight line parallel to the time axis
(b) a straight line passing through the origin
(c) an S-shaped curve passing through the origin
(d) an S- shaped curve that does not pass through the origin.

16. An isothermal gas phase reaction, A ® 5B is being conducted initially with pure A. The expansion factor for this reaction, Î A=
(a) 1                 (b) 2                (c) 3                 (d) 4

17. An isothermal gas phase reaction, A ® 5B, is being conducted by taking 50% A and 50% inert at start. Î A
(a) 1                 (b) 2                (c) 3                 (d) 4

19. Half – life period for a first order reaction is
(a) t1⁄2 = 1/k
(b) t
1⁄2 = 0.393/k
(c) t
1⁄2 = 0.473/k
(d) t
1⁄2 = 0.693/k

21. An isothermal gas phase reaction, A ® 3B, is being conducted by starting with pure A in a variable volume batch reactor. Initially, the reactor volume is 1 L. When 50% conversion of A has been achieved, reactor volume is
(a) 1 L             (b) 1.5 L          (C) 2.L            (D) 3 L

22. A plot of lnk vs. 1/T is known as
(A) Bode diagram
(B) Van’t Hoff plot
(C) Arrhenius plot
(D) none of these

23. A homogeneous liquid phase reaction is conducted in a batch stirred reactor at a speed of agitation of 500 rpm. If the speed of agitation is doubled,
(A) the reaction rate will double
(B) the reaction rate will be halved
(C) the reaction rate will remain unaffected
(D) the reaction rate will decrease by a factor less than two

24. Batch reactors are industrially used
(a) for production of fine chemicals
(b) for production of heavy chemicals
(d) when relatively small amount of materials are to be treated (d) for conducting fermentation

25. In fermentation processes, batch reactors are traditionally preferred because
(a) the interval between batches provides an opportunity to clean the system thoroughly and ensure that no deleterious intermediates and foreign bacteria build up and spoil the product
(b) products on fermentation do not have much demand and are, therefore, produced only in small amounts for which the use of continuous flow reactors is not justified
(c) no temperature and concentration gradients exist in batch reactors and fermentation occurs under uniform conditions
(d) I do not agree with the statement that batch reactors are preferred for fermentation. Fermentation is always conducted in flow reactors. So answers (a), )b) and (c) are meaningless.

26. An ideal plug flow reactor should have the following characteristics
(a) no back mixing of the reactants and products
(b) complete back mixing of the reactants and products
(c) uniform temperature, pressure and composition across any section normal to the fluid motion
(d) uniform temperature, pressure and composition at any location in the longitudinal direction

27. For efficient heat transfer to and from a jacketed reactor, the reactor configuration should have
(a) low surface-to-volume ratio
(b) high surface-to-volume ratio
(c) any surface-to-volume ratio because heat transfer does not depend on surface-to-volume ratio

28. A homogeneous liquid phase reaction A ® B occurs in a batch reactor and a conversion of 50% is achieved in one hour. If the same reaction is conducted in a plug flow reactor the space time necessary for 50% conversion is
(a) 1 s (b) 1 min (c) 1 hr (d) between 1 min and 1 hr

29. The dimension of "space velocity" is
(a) [ length ] [time-1
(b) [ time-1 ]

30. A “space time” of 5 minutes means
(a) 100% conversion of the reactant is achieved in 5 minutes
(b) One reactor volume of feed at specified conditions is processed in 5 minutes. (c) 5% conversion is achieved in one minute
(d) none of these

31. If "space time" is denoted by and "space velocity" by s, then(a) . s = 0 (b) . s = 1(c. s = 0.1 (d. s=any value greater than zero

32. One liter/min of liquid containing a reactant A at a concentration of 0.2 mol/l flows into a continuously operated ideal flow stirred tank reactor. The outflow from the reactor contains A at a concentration of 0.02 mol/l. If the volume of the reactor is 2 lit, the rate of reaction of A realized in the reactor is
(a) 0.02 mol/l. min (b) 0.09 mol/l. sec (c) 0.09 mol/ l. min (d) 0.18 mol/ l. min

33. A space velocity of 10 hr-1 means
(a) the linear velocity of the reactant through the reactor is 10 ft/hr
(b) it takes 10 hrs for complete conversion of the reactant to product
(c) ten reactor volumes of feed at specified conditions are being supplied to the reactor (d) none of these.

34. For a plug flow reactor,
(a) axial diffusivity is infinite, radial diffusivity is zero
(b) axial diffusivity is zero, radial diffusivity is zero
(c) axial diffusivity is zero, radial diffusivity is infinite
(d) axial diffusivity is infinite, radial diffusivity is infinite

35. In order to realize a specified conversion for a zero order reaction, volume of a CSTR is
(a) more than the volume of a PFR
(b) less than the volume of a PFR
(c) equal to the volume of a PFR
(d) twice the volume of a PFR

36. A second-order reaction is to be conducted in a battery of two mixed reactors of unequal volumes in series. Now, under otherwise uniform conditions of flow rates and temperature, etc., higher conversion of reactant can be realized if the battery is so arranged that
(a) the bigger reactor comes first and the smaller reactor comes next
(b) the smaller reactor comes first and the bigger reactor comes next
(c) either (a) or (b) holds because total volume in both cases is the same and it is the total reactor volume that matters in consideration related to conversion.

37. A first order reaction is to be conducted in a series of two mixed reactors. Total volume of the two reactors is minimum when
(a) the reactors are equal in size
(b) the ratio of volumes of the first and second reactor is 2 : 1. (c) the ratio of volumes of the first and second reactor is 1 : 2 (d) none of the above is true

38. A zero order reaction is conducted in a CSTR. If, under otherwise uniform conditions, the reactant concentration in the fluid entering the reactor is halves, the fractional conversion of the reactant will
(a) decrease by a factor of two
(b) increase by a factor of two
(c) remain unaffected because rate of a zero order reaction is independent of concentration
(d) I do not agree with the problem statement; a zero order reaction is never conducted in a CSTR. A PFR should be employed for this purpose.

39. A first order reaction is conducted in a CSTR. If, under otherwise uniform conditions, the reactant concentration in the fluid entering the reactor is doubled, the fractional conversion of the reactant will
(a) increase by a factor of two
(b) decrease by a factor of two
(c) remain unaffected because fractional conversion of the reactant is independent of concentration for a first order reaction

40. At present a zero order reaction is being conducted in a PFR of volume V and a fractional conversion of 0.50 is realized. If a 2nd PF reactor of volume V is now added to the first reactor, the reactant concentration in the fluid exiting the battery of two PFRs will be
(a) zero
(b) 25% of the reactant concentration in the fluid entering the first reactor
(c) 50% of the reactant concentration in the fluid entering the second reactor
(d) either (a) or (b)

41. In a recycle reactor the recycle ratio is zero. This means the reactor is basically a
(a) PFR
(b) CSTR
(c) PFR with zero radial mixing
(d) PFR with substantial axial dispersion

42. An autocatalytic reaction A + R ® R + R is best conducted in a CSTR provided (a) the level of conversion is high
(b) the level of conversion is low (c) the feed flow rate is low
(d) the feed flow rate is high

43. An autocatalytic reaction A + R ® R + R is to be conducted in a CSTR. Now minimum CSTR volume results when the fractional conversion of A is
(a) 0.25            (b) 0.50           (c) 0.75            (d) 0.90

44. For a zero order reaction volume of a CSTR is equal to the volume of a PFR for the same conversion level of the reactant. Identify from the following the case where CSTR volume is equal to PFR volume :
(a) solid catalyzed vapour phase reaction of any order (b) homogeneous reactions of fractional order
(c) autocatalytic reaction
(d) gas-liquid reaction

45. For an autocatalytic reaction A + R ® R + R a fractional conversion (of A) of 90% is desired. Which of the following will give minimum total reactor volume so as to achieve the desired conversion level?
(a) a PFR up to a conversion level of 50% and subsequently a CSTR to achieve final conversion
(b) a single PFR
(c) a CSTR up to a conversion level of 50% and subsequently a PFR to achieve final conversion
(d) two CSTRs in series; the conversion level in the first reactor is 50%

46. Combustion of a fuel gas in an adiabatic furnace with cool reactants being fed into the system is an example of an autocatalytic reaction. Which of the following sustains the combustion process and hence, may be called product having autocatalytic behaviour ?
(a) Carbon dioxide
(b) Water vapour
(c) Fuel gas itself
(d) Air supplied for combustion

47. For an autocatalytic reaction A + R ® R + R, maximum rate is realized at a conversion level of (a) 25%           (b) 50%           (c) 75%           (d) none of the above

48. A certain process employs a recycle reactor and the recycle ratio is set at a value of one. This suggests volume of fluid returned to the reactor inlet is equal to
(a) volume of fluid entering the reactor
(b) volume of fluid leaving the system
(c) half of the volume of fluid leaving the system (d) zero

49. A zero order reaction is to be conducted in a battery of three reactors in series. The battery consists of one small CSTR of Volume V/4 lit, a large CSTR of volume V lit, and a PFR of volume V/2 lit. Which of the following arrangements will give highest conversion of the reactant under otherwise uniform conditions ?
(a) PFR!Small CSTR!Large CSTR
(b) PFR
!Large CSTR!Small CSTR
(c) Large CSTR
!PFR!Small CSTR
(d) All arrangements shown above will give the same conversion

50. In question no. 49, if the order of the reaction is 0.5, which one of the arrangements (a) to (d) will give highest conversion ?
(a) PFR!Small CSTR!Large CSTR
(b) PFR
!Large CSTR!Small CSTR
(c) Large CSTR
!PFR!Small CSTR
(d) All arrangements shown above will give the same conversion

51. A first order reaction is being conducted in a battery of N-mixed reactors of equal volume in series and the following result is known for the ratio of concentration of A in the stream leaving the N-th reactor in the battery and concentration of A in the stream entering the first reactor in the battery : What happens to the behaviour of the battery when N ® ¥ ?
(a) behaves like a single CSTR of volume V( V= volume of single reactor)
(b) behaves like a single CSTR of volume NV
I(c) behaves like a PFR of volume Vi(d) behaves like a PFR of volume NV

52. A homogeneous zero-order reaction is conducted in a PFR at 1000C and a reactor volume of V lit is required for realizing a specified conversion. If the same reaction is conducted at1100C, what will be the required reactor volume for the same conversion level as above under otherwise uniform conditions? The activation energy of the reaction is 84 KJ/mole.
(a) V L            (b) V/2 L         (c) V/4 L        (d) V/6 L

53. For multiple reactions 2A ® R, 2R ® S,the number of moles of S present when the number of moles of A and R are 0.4 and 0.5 respectively (initially 2 moles of A are present only) are
(a) 0.125          (b) 0.150         (c) 0.200          (d) 0.400

54. Consider a homogeneous reaction of the type and also . R is the desired product and its concentration is to be maximized by selection of a proper reactor. Which reactor system will you choose in order to get the highest R – concentration (under otherwise uniform conditions)?
(a) Batch reactor
(b) PFR
(c) single CSTR
(d) Five CSTRs in series

57. Consider the following reaction scheme :A + B ® R; R + B ® S. If A is added drop wise into a batch stirred reactor containing only B, the products formed will contain
(a) only R
(b)
only S
(c) a mixture of R and S. R will form and its concentration will rise to a maximum and then will decrease. S concentration will increase slowly. In the final product 50% R and 50% S will be present.
(d) a mixture of R and S. Both concentrations will steadily rise right from the beginning until an equimolar mixture results.

58. A series reaction is conducted in a batch reactor and Cas a
function of time is given by the following equations : . If k= k2, then CR/CAO is equal to

59. A series reaction, is being conducted in a PFR. To maximize the production of R, the optimum space time should be equal to

60. Suppose the reaction in question is conducted in a CSTR . The optimum space time for the production of R for this case is

61. For the reaction type, A!R and A!S ,the fractional yield of the desired product, R, is not influenced by the reactor type ( i. e. the same fractional yield of R is realized whether the reaction is conducted in a batch reactor, CSTR or PFR ) . From this information what idea do you get about the kinetics of the reaction ?
(a) both reaction A to R and A to S are of the same order
(b) A
® R is zero order, but A ® S is first order
(c) A
® R is first order, but A ® S is zero order
(d) A ® R is 2nd order, but A ® S is zero order

68. An exothermic homogeneous reaction is being conducted in an isothermal batch reactor and for a specified conversion the batch time required is t. If the reaction is now conducted in an adiabatic batch reactor, the batch time will be
(a) more than t
(b) less than tB(c) equal to tB(d) data insufficient, so nothing can be said about the batch time in the adiabatic reactor

I69. f the total enthalpy of products is less than the total enthalpy of the reactants, the reaction is
(a) endothermic
(b) exothermic
(c) either (a) or (b)

74. Consider a reversible gas-phase reaction is increased, equilibrium conversion of the reactant. The reaction is exothermic. If the system pressure
(a) decreases
(b) increases
(c) remains unaffected by pressure changes
(d) may increase or decrease, depending on the magnitude of heat of reaction.

75. For a gas-phase reaction , if some inerts are added into the system under otherwise uniform conditions, conversion of A will
(a) decrease     (b) increase     (c) remain unaffected

76. For a reversible endothermic reaction, with increase in temperature,
(a) rate of reaction increases
(b) equilibrium conversion increases
(c) both rate and equilibrium conversion increase
(d) neither rate nor equilibrium conversion increases

77. A reversible endothermic reaction is to be conducted in a flow reactor. Now in order to achieve a specified conversion in a reactor of minimum volume, what operating temperature will you select ?
(a) temperature as low as possible
(b) highest possible temperature
(c)the material of construction of the reactor vessel must withstand the temperature
(d) varying temperatures; along the locus of maximum rates known as optimum temperature progression

78. For a reversible exothermic reaction, with increase in temperature,
(a) rate of reaction increases
(b) equilibrium conversion increases © rate of reaction decreases
(d) equilibrium conversion decreases

79. A reversible exothermic reaction is to be conducted in a flow reactor. In order that a specified conversion is realized in a reactor of minimum volume, the reaction should be conducted
(a) at the lowest possible temperature
(b) at the highest possible temperature
(c) at varying temperatures; along the locus of maximum rates, known as optimum temperature progression

82. For a consecutive reaction the activation energies are Eand Erespectively and E>> E2. Now maximum selectivity for B can be realized by conducting the reaction at
(a) the highest allowable temperature
(b) the lowest allowable temperature
(c) an intermediate temperature
(d) any temperature because selectivity is independent of temperature

83. A high temperature favours the reaction of .............(i) activation energy ; low temperature favours the reaction of ............(ii) activation energy
(a) higher        (b) lower

84. For a consecutive reaction the activation energies are Eand Erespectively If E= E2, increase in temperature
(a) will increase the selectivity for B
(b) will increase the selectivity for C
(c) will have no influence on the selectivities for B and C

(d) will cause a reduction in selectivity for B

85. Consider the reaction; R is the desire product. Step (1) has an activation energy of 20 kcal/mol and Step (2) has an activation energy to 10 kcal/mol. In order to promote the production of R, the reaction should be conducted
(a) at the lowest possible temperature
(b) at the highest possible temperature
(c) at an intermediate temperature (between the highest and the lowest temperature)
(d) in accordance with a temperature progression; low temperature followed by high temperature.

86. Statement is sometimes made " a reaction doubles in velocity for each 10rise in temperature". If this is true for temperatures 300 K and 310 K, the activation energy of the reaction in cal/mol is
(a) 1000           (b) 5000          (c) 12806         (d) 18772        (e) 25000

87. If the statement given in question (86) is true for temperatures 373 K and 383 K, the activation energy of the reaction in Cal/mol is
(a) 10 000        (b) 12 689       (c) 19 671        (d) 33 481       (e)none of these

88. By what factor will the rate constant be increased between 298K and 308 K if the activation energy is 35 000 cal/mol?
(a) by a factor 1.35 (b) by a factor 1.92 (c) by a factor 2.79 (d) none of the above

89. Consider the reaction given below. In order to promote the formation of B, the reaction should be conducted
(a) at the highest possible temperature
(b) at the lowest possible temperature
(c) at an intermediate temperature
(d) in accordance with a falling temperature progression : high temperature followed by low temperature.

90. Knowledge of fluid dynamics is important for reactor design.
(a) This is because frequency factor and hence, the rate constant depends strongly on the fluid flow pattern
(b) If the complete velocity distribution map is known, the residence time of the reactant within the reactor will be known correctly and conversion can be accurately predicted

(c) Fluid dynamics and reactor design are two entirely different areas. Reactor design, therefore, does not require any information about fluid flow patterns, etc. I, therefore, do not agree with the statement of the question.

100. Conversion of the reactant can be accurately predicted by knowing the residence time distribution for
(a) first – order reaction (b) second – order reaction (c) half – order reaction (d) all of the foregoing

101. Which of the following models (for predicting conversion from RTD data) contains (s) zero adjustable parameters?
(a) Tanks- in – series model
(b) dispersion model (c)Segregation model
(d) Maximum mixed ness model

102. Which of the following models contains (s) one adjustable parameter?
(a) Dispersion model
(b) Segregation model
(c) Maximum mixed ness model

103. In RTD studies the differential equation is well-known. The equation occurs in
(a) Tanks-in-series model
(b) Segregation model

(c) Axial dispersed plug flow model (d) Maximum mixed ness model
104. Which of the following dimensionless groups is called Peclet
number (: momentum diffusivity ; : thermal diffusivity)

105. For an ideal plug flow reactor the dispersion number, , is
(a) 1 (b) 0 (c) infinity (d) none of the foregoing

106. A fluid is flowing laminarly through a pipe. If, under otherwise uniform conditions, packing particles re introduced in the pipe,
(a) flow will approach plug flow more closely
(b) flow will still be laminar with non improvement in mixing characteristics

(c) fluid backmixing will increase

108. In residence time distribution studies of chemical reactors, terms like macrofluid and microfluid find wide usage. Now a macrofluid is basically(a) a large volume of fluid
(b) a fluid in which molecules are free to more everywhere

(c) a fluid in which the elements of a given age do not mix with other elements
(d) none of the foregoing

109. The basic difference between macromixing and micromixing is that
(a) macromixing does not specify how fluid molecules of different ages encounter one another in the reactor
(b) macromixing describes how fluid molecules of different ages encounter one another in the reactor

110. The segregation model will give the highest conversion for reaction order
(a) less than one
(b) equal to one
(c) greater than one
(d) equal to zero

111. The complete mixing model will give the highest conversion for reaction order
(a) <1 (b) 1 (c) >1 (d) none of the foregoing

112. A solid-catalyzed vapour phase reaction is irreversible and intrinsically second –order with respect to the reactant concentration. Laboratory experiments, however, show that the reaction is first-order with respect to the reactant concentration. What can you conclude from such experimental results ?
(a) The reaction is kinetically – controlled (surface – reaction controlling)
(b) Possibly the catalyst is porous and under reaction-conditions employed, diffusion and reaction might occur simultaneously. Because of strong pore-diffusion limitation a 2nd order reaction appears as if it is a first-order reaction.
(c) Possibly the reaction is controlled by transport of reactant from the bulk gas phase to the catalyst surface, or in other words, the reaction is external film-resistance controlled.
(d) Nothing can be concluded and new experiments should be conducted. One should remember that an intrinsically 2
nd – order heterogeneous reaction, under no conditions, can show first-order dependence with respect to the reactant concentration. The experimenter has collected wrong data and should not be relied upon.

113. A solid – catalyzed vapour phase reaction has been conducted in the laboratory. A highly porous catalyst has been employed and it has been proved beyond doubt that, under reaction – conditions employed, only the external surface area of the catalyst is active. If, under otherwise uniform conditions, reaction temperature is increased further,
(a) more active surface area ( actually taking part in reaction) will be utilized for reaction (b) less active surface area will be utilized for reaction
(c) same active surface area will be utilized, but still global reaction rates in kmol/m .s may be different
(d) same active surface area will be utilized and global reaction rate will reach a constant value. There after increase in temperature will have absolutely no effect on reaction rates.

114. For a certain gas-solid reaction occurring in presence of a nonporous catalyst particle global reaction rate at steady state is given by. what is the "intrinsic" order of the reaction (a) 0     (b) 1    (c) 2     (d) 0.5

115. For the rate equation given in question (114), which of the following is appropriate ?
(a) the reaction is kinetically – controlled (surface-reaction controlling)
(b) the reaction is controlled by mass transfer of reactant from the bulk gas phase to the catalyst surface
(c) both mass transfer and chemical reaction on the surface are important and they are steps in series
(d) both mass transfer and chemical reaction on the surface are important and they are steps in parallel

116. For a certain gas-solid reaction occurring in presence of a nonporous catalyst particle, the global reaction rate at steady state is given by
the intrinsic order of the reaction is
(a) 0.5              (b) 1                (c) 2                 (d) 0

119. For low values of Thiele modules, effectiveness factor tends to
(a) 0 (b) 1 (c) 2 (d) -1

120. In order to realize high effectiveness factor of a catalyst particle, one should employ
(a) small catalyst particles (b) low reaction temperature
(c) catalyst having large pores (d) all of the above

121. A plot of effectiveness factor (h) vs. Thiele modulus (f) on a log-log graph paper looks like the one given below:
(a) 1 (b) -1 (c) 2 (d) -2

122. For a porous catalyst particle where reaction and diffusion occur simultaneously, which of the following statements is/are appropriate?
(a) Diffusion and reaction occur in series
(b) Diffusion and reaction occur in parallel
(c) Reaction may be controlled by diffusion

123. An intrinsically second – order reaction, when conducted in presence of a porous catalyst particle under conditions of strong pore diffusion limitation, appears to be a(a) first order reaction
(b) one and a –half order reaction
(c) second order reaction
(d) two and a –half order reaction

124. Consider a gas-solid reaction being conducted in presence of a porous catalyst particle under conditions of strong pore diffusion limitation. The intrinsic activation energy of the reaction is 16 Kcal/mol. Under conditions of strong pore diffusion limitation the apparent activation energy (kcal/mol) is
(a) 4     (b) 8    (c) 12   (d) 16

125. An irreversible first order reaction occurs in presence of a spherical porous catalyst particle. The expression for effectiveness factor for a spherical catalyst particle is given by
Note R is the radius of the catalyst particle

126. For intrinsic reaction order equal to one, the effectiveness factor, corresponding to large values of Thiele modules,
(a) decreases with increasing reactant concentration at the external catalyst surface
(b) in independent of the reactant concentration at the external catalyst surface
(c) increases with increasing reactant concentration at the external catalyst surface.

127. The effectiveness factor (for large values of thick modules) decreases with increasing reactant concentration at the external catalyst surface for intrinsic reaction order equal to
(a) 0 (b) 1 (c) <1 (d) >1

128. The effectiveness factor can be significantly greater than one for a reaction which is
(a) exothermic and isothermal (b) endothermic and isothermal
(c) exothermic and non-isothermal (d) endothermic and non-isothermal

133. The reaction A ® B occurs in an isothermal catalyst pellet under steady state conditions. If the diffusion of A into the pellet is the rate-limiting step, the rate of diffusion of A is
(a) faster than the rate of reaction
(b) equal to the rate of reaction
(c) slower than the rate of reaction
(d) may be faster or slower, depending on the kinetics

135. When internal diffusion limits the overall rate of reaction, the reaction rate , the reaction rate
(a) Varies inversely with particle diameter, d
(b) Is independent of the gas velocity
(c) Exhibits an exponential temperature dependence which is not as strong as that for the surface reaction controlling reactions
(d) All of above

136. When external mass transfer controls the overall rate of a gas-solid reaction, the rate of reaction
(a) Varies inversely with dp3/2(b) is directly proportional to the square root of the velocity (c) increases approximately linearly with temperature
The mass transfer correlation for mass transfer coefficient for gas flow around a spherical catalyst particle is

137. The "Weisz – Prater criterion" enables us to obtain quick estimates from observed or measured quantities, which give an idea about the rate-limiting step in a heterogeneous reaction. The Weisz-Prater parameter is
defined by the dimensionless group , when the parameter value is much greater than one,
(a) intraparticle diffusion severely limits the reaction
(b) there are no intraparticle diffusion limitation
(c) external mass transfer controls the overall rate of reaction
(d) nothing can be concluded about the rate-limiting step

138. In order that no intraparticle diffusional limitations exist in case of a gas-solid reaction, the value of Weisz-Prater parameter should be
(a) >> 1
(b) =1

(c) << 1
(d) between 1 and 2

140. Consider a reaction scheme
reaction occurs in the presence of a solid catalyst. Under conditions of no pore diffusional limitation, selectivity for the desired product, B, is "S". If the reaction is now conducted under conditions of strong pore diffusional limitation, the selectivity for B will be
(a) greater than S
(b) less than S
(c) equal to S
(d) any of the foregoing, depending on the rate constants of the parallel steps

142. Consider a solid-catalyzed vapour phase reaction scheme . Reaction occurs in presence of a porous catalyst and a certain selectivity for the desired product B is obtained under conditions of no pore diffusional limitation. Assume that this selectivity is . If the reaction is now conducted under conditions of strong pore diffusion limitation, selectivity for B
(a) > (b) < (c) = (d) cannot be predicted, more information required

143. A porous solid catalyst has the following characteristics: particle density = 0.98 g/cm3; particle diameter = 0.6 mm; total surface area = 50 m2/g. The external surface area of the catalyst is(a) 50 m2/g
(b) 102.04 m
2/g
(c) 102.04 cm2/g
(d) 102.04 x 10
-4 cm2/g

144. A first-order irreversible gas-phase reaction is carried out on a catalyst of characteristic dimension (defined as volume of the catalyst particle divided by the external surface area) of 0.24 cm. The effective diffusivity of the reactant is 0.012 cm2/sec. The intrinsic rate constant at 100 0C is 1.0 s-1 and the intrinsic activation energy is 20 kcal/mole. The Thiele modulus for the catalyst at 100 0C is
(a) 0.57            (b) 1.19           (c) 1.74            (d) 2.19

145. For the problem in question no. (144), assume that the effective diffusivity is independent of temper            ture. Now Thiele modulus at 200 0C is
(a) 1.19            (b) 3.58           (c) 20.83          (d) 38.57

146. For a certain solid-catalyzed gas-phase irreversible first-order reaction, rate with very fine catalyst particle is 0.0302 mol/L. s. and that in presence of porous catalyst particle having characteristic dimension of 0.20 cm is 9.966 x 10-3 mol/L. s. The effectiveness factor of the porous catalyst is , therefore,
(a) 0.25            (b) 0.33           (c) 0.49            (d) 0.68

149. The Thiele modulus for a gas-phase first-order isothermal reaction for a spherical catalyst particle is found to be 2. The catalyst effectiveness factor is(a) 0.33 (b) 0.49 (c) 0.80 (d) 0.91150. Consider question number (149). Suppose the reaction is 2nd order instead of being first-order. For Thiele modulus equal to 2, the catalyst effectiveness factor
(a) < 0.80
(b) > 0.80
(c) = 0.80

151. For a certain gas-solid reaction Thiele modulus for a catalyst particle of slab geometry, based on the characteristic dimension, is equal to one. Under otherwise uniform conditions, Thele modulus for a spherical catalyst having the same characteristic dimension is equal to
(a) 1 (b) 2 (c) 3 (d) none of the foregoing

152. A gaseous reactant diffuses through a gas film and reacts on the surface of a nonporous spherical catalyst particle. The rate of surface reaction is k1CAs where CAs is the reactant concentration on the catalyst surface. The reaction rate constant k= 0.93 x 10-4 m/s and the gas-film mass transfer coefficient k= 1.53 x 10-4 m/s. If the rate expression in terms of bulk gas phase concentration CAg is written as k CAg, the value of k is
(a) 0.31 x 10-4 m/s (b) 0.578 x 10-4 m/s (c) 1.21 x 10-4 m/s (d) 1.59 x 10-4 m/s

153. Consider problem no. (152) suppose the reaction is gas film mass transfer controlled for a gas phase reactant concentration of 3.2 x 10-2 mol/L. If now the reactant concentration is reduced by a factor of 2 (under otherwise uniform conditions), the reaction(a) will still be gas-film mass transfer controlled
(b) will be surface – reaction controlled
(c) will be controlled by both gas-film and surface-reaction resistances
(d) rate will drop to zero

154. For the same characteristic dimension and under otherwise uniform operating conditions, the effectiveness factor for a spherical catalyst particle(a) is always higher than that for a flat plate
(b) is always lower than that for a flat plate
(c) is always equal to that for a flat plate
(d) may be any one of the foregoing depending on the molecularity of the reaction.

155. Consider a gas-phase exothermic reversible reaction being conducted in a non-isothermal packed bed reaction. The gas enters the reactor at 300 0C and a fractional conversion (close to equilibrium conversion) of 0.40 is achieved at the exit. A young Chemical engineer suggests that conversion can be markedly increased if the gas is preheated to 400 0C before it enters the reactor. Do you agree with the suggestion ? State with fractional conversion vs. temperature profile.(a) Yes, I agree.
(b) No, I don’t

(c) Yes, if the reaction is accompanied by an increase in number of moles from reactants to products.
(d) Yes, if the reaction is accompanied by a decrease in number of moles from reactants to products.