Chapter 3

Question 1

Is the net movement of a species in a mixture from one location to another

Answer 1

Mass Transfer

Question 2

_______ by a liquid of a solute from
a carrier gas involves transfer of the solute through the gas to the gas–liquid interface, across the interface, and into the liquid

Answer 2

Absorption

Question 3

transfer of the solute through the liquid to the liquid–liquid solvent interface, across the interface and into the solvent

Answer 3

Extraction

Question 4

Two mechanisms of mass transfer

Answer 4

molecular diffusion and
eddy (turbulent) diffusion

Question 5

-random and spontaneous microscopic movement of molecules as a result of thermal motion
-really slow

Answer 5

Molecular diffusion

Question 6

-random, macroscopic fluid motion
-rapid

Answer 6

eddy (turbulent) diffusion

Question 7

occurs in fluids when turbulent motion exist

Answer 7

eddy diffusion

Question 8

The total rate of mass transfer of individual species is increased or decreased by a ________

Answer 8

bulk flow

Question 9

-Third mechanism of mass transfer
-______alone does not provide a separation of the species in a mixture

Answer 9

bulk flow

Question 10

in _______, the extent of the separation is limited by phase equilibrium because with time, concentrations equilibrate by mass transfer

Answer 10

Multiphase systems

Question 11

When mass transfer is _______, equilibration takes seconds or minutes, and design of separation equipment can be based on phase equilibrium

Answer 11

rapid

Question 12

For separations involving barriers such as membranes, mass-transfer rates govern ________

Answer 12

Equipment design

Question 13

driven by composition gradients
(e.g., concentration, mole fraction,
activity, partial pressure), which is the most common type of diffusion in chemical separation processes

Answer 13

ordinary diffusion

Question 14

requires a large gradient, which is achieved for gas mixtures with a centrifuge

Answer 14

Pressure diffusion

Question 15

columns can be employed to
separate mixtures by establishing a
temperature gradient.

Answer 15

Thermal diffusion

Question 16

Widely applied is ________ of ions or charged particles in an electrical field

Answer 16

Forced diffusion

Question 17

Mass transfer by ordinary molecular diffusion in a binary mixture occurs because of a ___________; that is, a species diffuses in the direction of
decreasing concentration

Answer 17

Composition gradient

Question 18

The mass-transfer rate is ________ to the area normal to the direction of mass transfer. Thus, the rate can be expressed
as a ________.

Answer 18

Proportional, flux

Question 19

Net mass transfer stops when
concentrations are __________

Answer 19

uniform throughout

Question 20

He proposed an analogy to Fourier’s 1822 first law of heat conduction

Answer 20

Adolf Fick

Question 21

features a proportionality between a flux and a gradient.

Answer 21

Fick’s first law

Question 22

Driving potential for mass transfer

Answer 22

Concentration gradient

Question 23

Modes of mass transfer

Answer 23

Convection and diffusion

Question 24

occurs in solids and in fluids that
are stagnant or in laminar motion

Answer 24

Molecular diffusion

Question 25

occurs in fluids when turbulent motion exists

Answer 25

Eddy diffusion

Question 26

yields a mean-square distance of travel in a time interval but not in a direction interval

Answer 26

random-walk process

Question 27

is the molar flux (moles per unit perpendicular area and per unit time) of A by ordinary molecular diffusion relative to the molar-average velocity of the mixture in the z-direction

Answer 27

Ja (J sub A)

Question 28

is the mutual diffusion coefficient or diffusivity of A in B,

Answer 28

Dab

Question 29

Two cases are important for a binary mixture

Answer 29

(1) equimolar counter diffusion (EMD) and (2) unimolecular diffusion (UMD).

Question 30

takes place by mechanisms that depend on the diffusing atom, molecule, or ion

Answer 30

Diffusion in solids

Question 31

Mass transfer is characterized by Fick’s first law using a ________ mechanism involving the solubility, S, of the component at the polymer surface followed by diffusion throughout the polymer

Answer 31

solution-diffusion

Question 32

The distance, which increases with increasing distance x from the leading edge of the plate, is defined as the

Answer 32

velocity boundary-layer thickness

Question 33

Mass transfer occurs in

Answer 33

solids and in fluids that are stagnant or in laminar motion

Question 34

Molecular diffusion occurs by a number of different driving forces, including:

Answer 34

composition (ordinary), pressure, temperature, and external force fields

Question 35

two limiting cases of mass transfer in a binary mixture are:

Answer 35

equimolar counter diffusion (EMD) and unimolecular diffusion (UMD)

Question 36

a good approximation for distillation

Answer 36

equimolar counter diffusion (EMD)

Question 37

includes bulk-flow effects

Answer 37

unimolecular diffusion (UMD)

Question 38

what is anisotropic?

Answer 38

physical property that has a different value when measured in different directions; materials include fibrous and composite solids as well as noncubic crystals.

Question 39

diffusivity for ordinary molecular diffusion of solutes in a gas

Answer 39

0.10

Question 40

diffusivity for ordinary molecular diffusion of solutes in a liquid

Answer 40

1 x 10^(-5)

Question 41

diffusivity for ordinary molecular diffusion of solutes in an amorphous solid

Answer 41

1 x 10^(-9)

Question 42

Fick's second law for unsteady-state diffusion is readily applied to

Answer 42

semi-infinite and finite stagnant media, including anisotropic materials

Question 43

molecular diffusion under laminar-flow conditions is determined from

Answer 43

Fick's first and second laws, provided velocity profiles are available

Question 44

mass transfer flux is given by

Answer 44

the product of the mass transfer coefficient and a composition driving force

Question 45

mass transfer in turbulent flow can be predicted by

Answer 45

analogy to heat transfer

Question 46

utilizes empirical j-factor correlations with a Stanton number for mass transfer

Answer 46

Chilton-Colburn

Question 47

These predict mass-transfer coefficients proportional to the diffusivity raised to an exponent that varies from 0.5 to 1.0.

Answer 47

film theory, penetration theory, and surface-renewal theory

Question 48

is widely used to predict the mass-transfer flux from one fluid, across an interface, and into another fluid, assuming phase equilibrium at the interface

Answer 48

Whitman's two-film theory

Question 49

What does Whitman's two-film theory define

Answer 49

an overall mass-transfer coefficient determined from the separate coefficients for each of the phases and the equilibrium relationship at the interface