The Knudsen diffusivity is dependent on the (A) Molecular velocity only (B) Pore radius of the catalyst only (C) Molecular mean free path only (D) Molecular velocity and pore radius of the catalyst

The Knudsen diffusivity is dependent on the
(A) Molecular velocity only
(B) Pore radius of the catalyst only
(C) Molecular mean free path only
(D) Molecular velocity and pore radius of the catalyst
by

1 Answer

Answer :

(D) Molecular velocity and pore radius of the catalyst
by

Related questions

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 (A) Pressure (B) Temperature (C) Both (A) & (B) (D) Neither (A) nor (B)

Description : 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 (A) Pressure (B) Temperature (C) Both (A) & (B) (D) Neither (A) nor (B)

Last Answer : (B) Temperature

Effective diffusivity (DE) in a catalyst pellet is related to molecular diffusivity (DN) and Knudsen diffusivity (DK) as (A) DE = DM + DK (B) 1/DE = 1/DN + DK (C) DE = DM . DE (D) DE = DN/DE

Description : Effective diffusivity (DE) in a catalyst pellet is related to molecular diffusivity (DN) and Knudsen diffusivity (DK) as (A) DE = DM + DK (B) 1/DE = 1/DN + DK (C) DE = DM . DE (D) DE = DN/DE

Last Answer : (B) 1/DE = 1/DN + DK

The Knudsen diffusivity is proportional to (where, T = absolute temperature) (A) √T (B) T 2 (C) T (D) T 4

Description : The Knudsen diffusivity is proportional to (where, T = absolute temperature) (A) √T (B) T 2 (C) T (D) T 4

Last Answer : (A) √T

As per Gilliland's equation, the diffusivity is (A) Directly proportional to 'T 1.5 ' (B) Inversely proportional to 'P' (C) Dependent on the molecular volume & molecular weight of components (D) All 'a', 'b' & 'c'

Description : As per Gilliland's equation, the diffusivity is (A) Directly proportional to 'T 1.5 ' (B) Inversely proportional to 'P' (C) Dependent on the molecular volume & molecular weight of components (D) All 'a', 'b' & 'c'

Last Answer : (D) All 'a', 'b' & 'c'

The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which ‘D’ is the diffusivity of solute, is (A) D/a (B) D/2a (C) Proportional to √D (D) Dependent on the Reynolds number

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Last Answer : (D) Dependent on the Reynolds number

In fluid flow, and heat and mass transfer, one encounters (i) kinematic velocity (μ), (ii) molecular diffusivity (θ) and thermal diffusivity (α). The units of these quantities are. (A) μ , α and θ all have units of m/s (B) μ , α and θ all have units of m2/s (C) α and θ have units of m2/s, while μ has unit of m/s (D) α and θ have units of m/s, while μ has unit of m2/s

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Last Answer : Option C

For a first order isothermal chemical reaction in a porous catalyst, the effectiveness factor is 0.3. The effectiveness factor will increase if the (A) Catalyst size is reduced or the catalyst diffusivity is reduced (B) Catalyst size is reduced or the catalyst diffusivity is increased (C) Catalyst size is increased or the catalyst diffusivity is reduced(D) Catalyst size is increased or the catalyst diffusivity is increased

Description : For a first order isothermal chemical reaction in a porous catalyst, the effectiveness factor is 0.3. The effectiveness factor will increase if the (A) Catalyst size is reduced or the ... the catalyst diffusivity is reduced (D) Catalyst size is increased or the catalyst diffusivity is increased

Last Answer : (B) Catalyst size is reduced or the catalyst diffusivity is increased

Pick out the correct statement. (A) A lower temperature favours the reaction of lower activation energy (B) The dispersion number for a reactor/vessel is uL/D (C) The rate controlling step in a reaction involving many steps is the fastest step (D) Pore volume and porosity of a catalyst is measured by Brunauer￾Emmett-Teller (BET) technique

Description : Pick out the correct statement. (A) A lower temperature favours the reaction of lower activation energy (B) The dispersion number for a reactor/vessel is uL/D (C) The rate controlling step in ... step (D) Pore volume and porosity of a catalyst is measured by Brunauer￾Emmett-Teller (BET) technique

Last Answer : (A) A lower temperature favours the reaction of lower activation energy

Which of the following factors control the deactivation of a porous catalyst pellet? (A) Decay reactions (B) Pore diffusion (C) Form of surface attack by poison (D) All (A), (B) and (C)

Description : Which of the following factors control the deactivation of a porous catalyst pellet? (A) Decay reactions (B) Pore diffusion (C) Form of surface attack by poison (D) All (A), (B) and (C)

Last Answer : (D) All (A), (B) and (C)

The importance of diffusion in a catalyst are increased by (A) Large catalyst particle size (B) An active surface of the catalyst (C) Small pore diameter (D) All (A), (B) and (C)

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Last Answer : (D) All (A), (B) and (C)

In solid catalysed reactions the diffusional effects are more likely to affect the overall rate of reaction for (A) Fast reactions in catalyst of small pore diameter (B) Fast reaction in catalyst of large pore diameter (C) Slow reactions in catalyst of small pore diameter (D) Slow reactions in catalyst of large pore diameter

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Last Answer : (C) Slow reactions in catalyst of small pore diameter

Pick out the wrong statement. (A) Exit age description function (E) and internal age distribution function (I) are related as, E = -(dI/dθ) (B) Chemisorption studies are useful in the determination of catalyst surface area and pore size distribution (C) A higher temperature favours the reaction of higher activation energy (D) A catalyst increases the potential energy barrier over which the reactants must pass to form products

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Last Answer : (D) A catalyst increases the potential energy barrier over which the reactants must pass to form products

If Thiele modulus is __________, then the pore diffusion resistance in a catalyst may be considered as negligible. (A) 0 (B) ∞ (C) < 0.5 (D) > 0.5

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Last Answer : (C) < 0.5

Helium-mercury method can be used to determine the __________ of the catalyst particle. (A) Pore volume (B) Solid density (C) Porosity (D) All (A), (B), & (C)

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Last Answer : (D) All (A), (B), & (C)

Helium-mercury method is used for the measurement of the __________ of the catalyst. (A) Surface area (B) Porosity (C) Pore volume (D) Both (B) & (C)

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Last Answer : (D) Both (B) & (C)

If pore diffusion is the controlling step in a solid catalysed reaction, the catalyst (A) Porosity is very important (B) Porosity is of less importance (C) Internal surface area is utilised efficiently (D) None of these

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BET apparatus is used to determine the (A) Specific surface of a porous catalyst (B) Pore size distribution (C) Pore diameter (D) Porosity of the catalyst bed

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Effectiveness factor of a catalyst pellet is a measure of the __________ resistance. (A) Pore diffusion (B) Gas film (C) Chemical reaction (D) None of these

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Bulk diffusion in catalyst pore __________ with increase in pressure. (A) Increases (B) Decreases (C) Remains unchanged (D) Increases exponentially

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. B.E.T. method can be used to determine the __________ of a porous catalyst. (A) Solid density (B) Pore volume (C) Surface area (D) All (A), (B) and (C)

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Effectiveness factor (E) of a catalyst pellet is defined as, E = (actual rate within pore of the catalyst)/(rate if not snowed by pore diffusion), Effectiveness factor for a first order reaction is given by (where, T = Thiele modulus) (A) tan hT/T (B) tan T/T(C) tan hT/tan T(D) None of these

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In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the (A) Temperature and pressure (B) Concentration (C) Nature of the constituents (D) None of these

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Pick out the correct statement. (A) Diffusivity decreases with increase in temperature (B) Diffusivity increases with increase in molecular weight (C) Diffusivity increases with the size of the individual molecule (D) None of these

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According to the film theory of mass transfer, the mass transfer co￾efficient is proportional to (where, D = molecular diffusivity). (A) D (B) D2 (C) D0.5 (D) 1/D

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Molecular diffusivity of a liquid (A) Increases with temperature (B) Decreases with temperature (C) May increase or decrease with temperature (D) Is independent of temperature

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