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The CORRECT CHOICE is (a) True

To elaborate: Increase in pump speed do not change the OVERALL reaction rate. Therefore, if we can identify a liquid velocity u*L at which reaction rate becomes independent of liquid velocity, OPERATION at uL > u*L will ensure that ηC = 1.

The correct CHOICE is (b) Domestic refrigerator

Easy explanation: Air COOLED CONDENSERS are of two types: natural CONVECTION and forced convection. In the natural convection type, the air flows over it in natural a way depending upon the temperature of the condenser coil. In the forced air type, a FAN operated by a motor blows air over the condenser coil.

The correct choice is (B) False

Best explanation: In heterogeneous REACTORS external mass transport can be increased by a better mixing of the fluid. A higher flow rate also contributes to a better mixing. Under the better mixing a laminar film around the CATALYST particle is thinner and more REACTANTS can be transported to the surface. CONSEQUENTLY, the overall conversion of reactants can be increased in spite of lowering of the residence time.

The CORRECT CHOICE is (a) mass of catalyst remains unchanged

Explanation: Catalyst is defined as a substance, which alters the rate of a chemical reaction, itself remaining CHEMICALLY unchanged at the end of the reaction. The process is CALLED Catalysis.

Correct choice is (a) True

Easy explanation: If the reaction is endothermic, the temperature at the catalyst surface will be less than the bulk fluid temperature and the observed rate will be less than that determined at the bulk fluid temperature. If the reaction is exothermic, the temperature of catalyst surface will be more than the bulk fluid temperature. THEREFORE, the observed rate will be higher or LOWER than corresponding bulk fluid conditions, depending on both heat TRANSFER and mass transfer effects. Rate at the surface will be higher due to heat transfer limitations and lower due to mass transfer limitations. Depending on the relative MAGNITUDE, the overall rate will be INCREASED or decreased.

The correct OPTION is (a) Directly

Explanation: Concentration of the REACTANTS is directly proportional to the NUMBER of COLLISIONS and also directly proportional to the reaction RATE. The more the collision, more will be the reaction rate and hence more will be the concentration of reactants.

The correct option is (a) CAS = CAb

To ELABORATE: Ω is an OBSERVABLE modulus for EXTERNAL MASS transfer. If Ω << 1, CAS = CAb and external mass-transfer effects are insignificant. Otherwise, CAS < CAb and external mass-transfer effects are significant.

Correct ANSWER is (d) Ω

Explanation: The OVERALL effectiveness factor (BASED on CAB) is DEFINED as:

Correct choice is (b) 0.015 s^-1

The BEST explanation: K I = 3.11×10^5 s^-1kg^-1(4.83 x 10^-8 KG) = 0.015 s^-1.

The correct CHOICE is (C) The REACTANTS and catalyst are in the same rate

The EXPLANATION is: Homogeneous catalysis refers to catalytic reactions where the catalyst is in the same phase as the reactants. Homogeneous catalysis applies to reactions in the gas phase and even in solids.

The CORRECT CHOICE is (b) False

The best explanation: In large-scale reactors, external mass-transfer problems may be unavoidable if sufficiently HIGH liquid velocities cannot be achieved. However, when evaluating biocatalyst kinetics in the laboratory, it is advisable to eliminate fluid boundary LAYERS to simplify analysis of the DATA. Several laboratory reactor configurations allow almost complete elimination of interparticle and interphase concentration gradients. Operation with high liquid velocity through the bed reduces boundary-layer effects.

Correct answer is (C) INCREASE the RADIUS R

The best EXPLANATION: Internal diffusion limits the observed rate when decreasing dp increases –r’A . If the rate increases when dp decreases but does not change with FT0, then larger dp is LIMITED by internal diffusion. (where, FT0 is the particle size, dp is the diameter and –r’A is the reaction rate).

Correct OPTION is (b) External mass-transfer

For explanation: External mass transfer is more RAPID at high BULK substrate concentrations; the higher the concentration, the greater is the driving FORCE for mass transfer across the boundary layer.

The CORRECT choice is (b) Schmidt number

For explanation: Schmidt Number, Sc, is a dimensionless parameter representing the RATIO of diffusion of MOMENTUM to the diffusion of mass in a FLUID. It is defined as

Sc = v/δ

where ν is kinematic viscosity and &delta diffusivity.

Schmidt number is the mass transfer equivalent of Prandtl Number. For gases, Sc and Pr have similar values (≈0.7) and this is USED as the basis for simple heat and mass transfer analogies.

The correct option is (b) False

For EXPLANATION: K1 is the intrinsic first-order rate constant with dimensions T^-1, whereas, k0 is the intrinsic zero-order rate constant with units of, for EXAMPLE, g mol s^-1 m^-3particle.

Correct OPTION is (a) Sherwood number

The explanation: The Sherwood number (Sh) (also called the mass transfer NUSSELT number) is a dimensionless number USED in mass-transfer operation. It represents the ratio of the CONVECTIVE mass transfer to the rate of diffusive mass transport.

The CORRECT choice is (c) m/min

The explanation: The rate, EXPRESSED in FEET (meters) per minute, at which a given size and shape of rock particle will descend or SETTLE in WATER; e.g., the slip velocity in water of a round, flat particle of rock, 1/2 in (1.27 cm) in diameter, is about 54 ft/min (16.5 m/min).

The correct answer is (d) Grashof number

The BEST explanation: The Grashof number (Gr) is a DIMENSIONLESS number in fluid dynamics and HEAT TRANSFER which approximates the ratio of the buoyancy to viscous force acting on a fluid. It frequently arises in the study of situations involving natural convection and is analogous to the Reynolds number.

Correct choice is (d) Reynolds number

The best I can EXPLAIN: The Reynolds number is the ratio of inertial forces to viscous forces and is a convenient PARAMETER for predicting if a flow CONDITION will be laminar or TURBULENT. It can be interpreted that when the viscous forces are dominant (slow flow, low Re) they are sufficient enough to keep all the fluid PARTICLES in line, and then the flow is laminar. Even very low Re indicates viscous creeping motion, where inertia effects are negligible. When the inertial forces dominate over the viscous forces (when the fluid is flowing faster and Re is larger) then the flow is turbulent.

The correct option is (C) Change in mass

The explanation: A CATALYST is a species that SPEEDS up a CHEMICAL reaction without being CHEMICALLY changed upon completion of the reaction. In other words, the mass of a catalyst is the same before and after a reaction occurs.

Correct choice is (a) True

The best EXPLANATION: When the catalyst is very active with a high demand for substrate, mass TRANSFER is likely to be slow relative to reaction so that steep CONCENTRATION gradients are produced. However, limiting the reaction rate by operating at sub-optimum conditions or using an organism or enzyme with low intrinsic ACTIVITY does not achieve the overall goal of higher conversion rates. Because rA,obs is the reaction rate per volume of catalyst, another WAY of reducing rA,obs is to reduce the cell or enzyme loading in the solid. This reduces the demand for substrate per particle so that mass transfer has a better chance of supplying it at a sufficient rate. Therefore, if the same mass of cells or enzyme is distributed between more particles, the rate of conversion will increase.

The correct OPTION is (c) Pressure

The explanation is: Increasing the pressure of a reaction improves the likelihood REACTANTS will INTERACT with each other, thus increases the rate of the reaction. As you would expect, this factor is important for reactions involving GASES, and not a significant factor with LIQUIDS and solids.

Right option is (d) CAs > CAb

The best I can explain: The term CAs is the concentration of substrate A at the external surface of the catalyst. This term made its WAY into the analysis in the BOUNDARY conditions used for solution of the shell mass balance.

Reduction in substrate concentration from CAb in the bulk liquid to CAs at the catalyst surface occurs ACROSS the boundary layer surrounding the solid. In the absence of the boundary layer, CAS = CAb, which is easily measured. When the boundary layer is present, CAs takes some value less than CAb.

The correct option is (a) True

Explanation: There are many factors that can either slow or speed up the RATE of a chemical reaction such as TEMPERATURE, pressure, concentration, and CATALYSTS. The Rate of a Chemical Reaction is always positive. It can be confusing since the Rate of Disappearance is negative, however when you think about it, a rate should NEVER be negative since the rate is describing how fast the concentration CHANGES with time. The units for the rate is Molarity per Seconds (M/s).

Correct CHOICE is (a) True

Explanation: A CATALYST provides an ALTERNATIVE pathway with a lower activation energy. Therefore, more PARTICLES have ENOUGH energy to overcome the new activation energy requirement.

Right answer is (b) False

To elaborate: RATE of catalytic surface reactions is proportional to the catalyst surface AREA. However, accessibility of that surface area is typically limiting, as most of it is INNER surface area inside the porous catalyst structure. Essentially all the surface area of most typical technical CATALYSTS is internal surface area. HENCE, a catalyst can only be used at its maximum potential, if diffusion inside the pore structure is not limiting.

Correct option is (a) 1.9 g m^-3

Easiest EXPLANATION: CAs/CAB= 1 – Ω = 0.63

CAs = 0.63 CAb = 0.63 (3 gm^-3) = 1.9 g m^-3.

Correct CHOICE is (B) The rate of reaction will decrease

The explanation is: Increasing the temperature increases reaction rates because of the DISPROPORTIONATELY LARGE increase in the number of high ENERGY collisions. It is only these collisions (possessing at least the activation energy for the reaction) which result in a reaction.

The CORRECT option is (c) Watt / m^2 k

Explanation: Heat flux form a bulk fluid at T∞ to the surface of a SPHERICAL particle of diameter dp at TS: Newtons law of COOLING:

q = h (T∞ – TS)

Where, q (Heat flux) = Watt / m^2

h (Heat transfer coefficient) = Watt / m^2K.

The correct OPTION is (B) Total flux = bulk motion + diffusion

The best explanation: Molar flux consists of two parts:

– Bulk motion of the fluid, BA

– MOLECULAR diffusion flux relative to the bulk motion of the fluid produced by a concentration gradient, JA

– WA = BA + JA (total flux = bulk motion + diffusion).

The correct answer is (a) True

To EXPLAIN: Concentration at the pore mouth will be higher than that INSIDE the pore, .i.e., internal diffusion which is diffusion of REACTANTS or products from particle surface (pore mouth) to pellet interior. And Mole balance over the SHELL THICKNESS Δr is: IN – OUT + GEN = ACCUM.

Correct option is (c) RAPID

To explain I would say: If a reaction PROCEEDS slowly even in the presence of adequate substrate, it is likely that mass transfer will be rapid enough to meet the reaction demand. In this case, the observed rate would be determined more directly by the reaction PROCESS than mass transfer. Conversely, if the reaction TENDS to be very rapid, it is likely that mass transfer will be too SLOW to supply substrate at the rate required.

Right choice is (a) Prandtl number

The explanation: The Prandtl number (Pr) or Prandtl group is a dimensionless number, It is defined as the RATIO of momentum diffusivity to thermal diffusivity. That is, the Prandtl number is given as:

where:

v : momentum diffusivity (KINEMATIC viscosity), v = μ/ρ, (SI UNITS: m^2/s)

α : thermal diffusivity, α = k/(cp ρ), (SI units: m^2/s)

μ : dynamic viscosity, (SI units: PA s = N s/m^2)

k : thermal conductivity, (SI units: W/m-K)

cp : specific heat, (SI units: J/kg-K)

ρ : density, (SI units: kg/m^3).

Correct answer is (B) False

Easiest explanation: In absence of mass transfer there is no difference in concentration of reactant at bulk and near the catalyst SURFACE. However, presence of significant mass transfer resistance results in a DECREASE in the concentration of reactants at the catalyst surface compared to that in the bulk fluid. Consequently, the observed RATE is less than the intrinsic rate evaluated at bulk fluid reactant concentration.

The correct choice is (b) False

To ELABORATE: The value of \(\mathcal{D}_{Ac}\) is a complex function of the molecular – diffusion characteristics of the SUBSTRATE, the tortuousness of the diffusion path within the solid, and the fraction of the particle volume available for diffusion. \(\mathcal{D}_{Ac}\) is CONSTANT and independent of substrate CONCENTRATION in the particle; this MEANS that \(\mathcal{D}_{Ac}\) does not change with position.

Correct choice is (b) False

For explanation I would say: Thiele MODULUS (Φ) is proportional to the square of catalyst size (R^2 for spheres or b^2 for flat PLATES), reducing the catalyst size has a more dramatic effect on Φ than changes in any other VARIABLE. It is therefore a good way to improve the reaction rate. In PRINCIPLE, mass-transfer limitations can be completely overcome if the particle size is decreased SUFFICIENTLY.

The correct option is (a) True

Explanation: The TERM advection SOMETIMES serves as a synonym for convection, but technically, convection covers the sum of transport both by diffusion and by advection. Advective transport describes the movement of some quantity VIA the bulk flow of a fluid (as in a RIVER or pipeline).

Correct answer is (b) False

Easy EXPLANATION: Removing the boundary LAYER would increase the value of CAS, thus establishing a greater driving force for internal mass-transfer and reducing the LIKELIHOOD of CA falling to zero inside the particle.