Chapter 4

Question 1

based on material and energy balances, equilibria, and rates of heat and mass transfer.

Answer 1

Quantitative treatment of mass transfer

Question 2

involve a knowledge of the equilibrium relationships between phases

Answer 2

All mass transfer calculations

Question 3

A limit to mass transfer is reached if

Answer 3

the two phases come to equilibrium and the net transfer of material ceases.

Question 4

The degree to which a separation can be achieved depends on _____________ of the individual components of the mixture, with limits dictated by thermodynamic phase equilibrium.

Answer 4

differing rates of mass transfer

Question 5

The choice of a mass-transfer operation for use in separating a mixture depends upon the

Answer 5

phase characteristics, equilibrium relationships, and chemical properties of the material

Question 6

Many separation operations are designed on the basis of the limit of attaining

Answer 6

thermodynamic phase equilibrium

Question 7

Equilibrium data are determined ___________

Answer 7

experimentally

Question 7

An understanding of the various __________________ is necessary in the selection of the
mass-transfer operation and most appropriate for a given separation.

Answer 7

phase-equilibrium relationships

Question 8

To evaluate driving forces, a knowledge of ________ between phases is therefore a basic importance

Answer 8

equilibria

Question 9

In all situations, ________ are involved, and all combinations are found except ______ gas phases or
________ solid phases, and the controlling variables are
the intensive properties T, P, and concentrations.

Answer 9

two phases, two

Question 10

equality of P between phases

Answer 10

Mechanical Equilibrium

Question 11

equality of T between phases

Answer 11

Thermal Equilibrium

Question 12

equality of chemical potential for a component for all phases in equilibrium

Answer 12

Physicochemical Equilibrium

Question 13

may be defined as a physically distinct and homogeneous portion of a system

Answer 13

PHASE

Question 14

The description of a single-stage system at physical
equilibrium involves ________ and
_____________

Answer 14

intensive variables and extensive variables

Question 15

independent of total quantity or size of system

Answer 15

INTENSIVE VARIABLE

Question 16

depends upon the total quantity or size of system

Answer 16

EXTENSIVE VARIABLE

Question 17

Regardless of whether only intensive variables or both intensive and extensive variables are
considered, only a few of the variables are independent; when these are specified, all other
variables become fixed.

Answer 17

The phase rule

Question 18

The number of _________ , or variance F , is the number of independent intensive variables-temperature, pressure, and concentrations – that must be fixed to define the equilibrium state of the system

Answer 18

degrees of freedom

Question 19

If fewer than variables are fixed –

Answer 19

an infinite number of states fit the assumptions.

Question 20

If too many are arbitrarily chosen

Answer 20

– the system will be overspecified and will be unable to reach an
equilibrium.

Question 21

Used to classify equilibria and to establish the degrees of freedom in a specific situation, applicable only to the intensive variables at equilibrium

Answer 21

The Gibbs phase rule

Question 22

Who stated the Gibbs phase rule?

Answer 22

J. Willard Gibbs in 1875

Question 23

The Gibbs phase rule is limited because

Answer 23

it does not deal with feed streams sent to the equilibrium stage nor with extensive variable

Question 24

the phase rule can be extended for process applications by

Answer 24

- adding feed stream and extensive variables - giving additional independent equations

Question 25

phase equilibrium is expressed in terms of

Answer 25

vapor-liquid & liquid-liquid K-values

Question 25

vapor-liquid and liquid-liquid K-values are formulated in terms of

Answer 25

fugacity and activity coefficients

Question 26

is the starting point for the derivation of commonly used equations for expressing phase equilibria

Answer 26

Gibbs free energy

Question 27

at equilibriumm, total G for all phases is a

Answer 27

minimum

Question 28

methods for determining the minimum G are referred to as

Answer 28

free-energy minimization techniques

Question 29

ratio of mole fractions of a species present in two phases at equilibrium

Answer 29

phase-equilibrium ratio

Question 30

for vapor-liquid equilibrium systems, the constant is referred to as

Answer 30

K-value (vapor-liquid equilibrium ratio or K-factor)

Question 31

for liquid-liquid equilibrium systems, the ratio is referred to as

Answer 31

distribution coefficient, partition coefficient, or liquid-liquid equilibrium ratio

Question 32

forming ratios of equilibrium ratios

Answer 32

separation factors

Question 33

vapor-liquid case separation factor

Answer 33

relative volatility

Question 34

liquid-liquid case separation factor

Answer 34

relative selectivity

Question 35

a simple expression used to describe gas (or vapor) liquid equilibrium

Answer 35

Raoult's Law

Question 36

raoult's full name

Answer 36

francois marie raoult (1882)

Question 37

when is raoult's law not applicable?

Answer 37

for mixtures with components having similar structure and properties

Question 38

when is raoult's law accurate?

Answer 38

only for an ideal solution in equilibrium with an ideal gas mixture

Question 39

in certain systems where raoult's law does not apply the phase composition can be predicted by

Answer 39

henry's law

Question 40

full name of henry from henry's law

Answer 40

william henry (1803)

Question 41

for ________, simple graphical representations of vapor-liquid equilibria data do not exist

Answer 41

multicomponent mixtures

Question 42

most often, data for multicomponent mixtures (including binary systems) is represented in terms of

Answer 42

K values

Question 43

K values are correlated _______ in terms of temperature, pressure, and composition

Answer 43

empirically or theoretically

Question 44

indicates the relative ease or difficulty of separating components

Answer 44

ratio of two K-values or relative volatility

Question 45

when relative volatility is ___, no separation by distillation is possible

Answer 45

1

Question 46

when is the compositions of the vapor and liquid identical and the two phases become one phase?

Answer 46

when relative volatility is 1, no separation by distillation is possible

Question 47

in the industry, distillation columns operate at _______ to be separated to _______

Answer 47

pressures well below the critical pressure of the mixture; to avoid relative volatilities that approach a value of 1

Question 48

for determining the effects of temperature and pressure on the K-values of hydrocarbons and light gases

Answer 48

nomographs

Question 49

are formed by liquid mixtures exhibiting maximum or minimum boiling points

Answer 49

azeotropes

Question 50

what does azeotropes represent

Answer 50

negative or positive deviations from raoult's law

Question 51

vapor and liquid compositions are identical at the

Answer 51

azeotropic composition

Question 52

at azeotropic composition, all K-values are ___ and _____

Answer 52

1; no separation of species can take place

Question 53

in azeotropic mixtures, if one liquid phase exists, the mixture forms a

Answer 53

homogeneous azeotrope

Question 54

in azeotropic mixtures, if more than one liquid phase is present, the azeotrope is

Answer 54

heterogeneous

Question 55

three types of azeotropes that are commonly encountered with binary mixtures

Answer 55

1. minimum-boiling homogeneous azeotrope 2. maximum-boiling homogeneous azeotrope 3. heterogeneous azeotropes (minimum boiling mixtures)

Question 56

azeotropes limit the separation achievable by

Answer 56

ordinary distillation

Question 57

How to shift the equilibrium in azeotropic mixtures?

Answer 57

1. by changing the pressure sufficiently 2. move it away from the region where the required separation must be made

Question 58

what will happen by changing the pressure sufficiently in azeotropic mixtures?

Answer 58

"break" the azeotrope

Question 59

high K-values favor

Answer 59

the vapor phase

Question 60

low K-values favor

Answer 60

the liquid phase.

Question 61

What two types of equations or data are used for single equilibrium stage calculations?

Answer 61

The two types of equations or data used for single equilibrium stage calculations are component material balances and K-value expressions.

Question 62

How do intensive and extensive variables differ?

Answer 62

Intensive variables are independent of mass, while extensive variables are related to the amount of mass or flow.

Question 63

What is meant by the number of degrees of freedom?

Answer 63

The number of degrees of freedom is the number of variables that must be specified so that the remaining variables can be determined from the independent equations.

Question 64

When a liquid and a vapor are in physical equilibrium, why is the vapor at its dew point and the liquid at its bubble point?

Answer 64

When a liquid and a vapor are in physical equilibrium, the vapor is at its dew point because that is the temperature at which the vapor starts to condense. The liquid is at its bubble point because that is the temperature at which the first bubble of vapor appears.

Question 65

What is the difference between a homogeneous and a heterogeneous azeotrope?

Answer 65

A homogeneous azeotrope is one where, at equilibrium, there is only one liquid phase. A heterogeneous azeotrope is one where, at equilibrium, there are two liquid phases.

Question 66

Why do azeotropes limit the degree of separation achievable in a distillation operation?

Answer 66

Azeotropes limit the degree of separation achievable in a distillation operation because at the azeotropic composition, the vapor and liquid phases have the same composition. This prevents further separation by distillation.

Question 67

three separation operations for relative volatility of a binary mixture

Answer 67

1. partial vaporization of the mixture when a liquid 2. partial condensation of the mixture when a vapor 3. multistage distillation

Question 68

binary azeotropic mixtures exhibit mainly ___________, where, under isobaric conditions, the azeotrope boils at a temperature below the boiling point of either of the pure components

Answer 68

minimum-boiling azeotropes

Question 69

where azeotropes boils at a temperature greater than the pure-component boiling points

Answer 69

maximum-boiling azeotropes

Question 70

a mixture of two or more components that forms a unique composition at which the liquid and vapor phases have identical compositions during boiling or condensation at a specific pressure.

Answer 70

azeotrope

Question 71

an example for minimum-boiling azeotrope

Answer 71

ethanol-water mixture

Question 72

an example for maximum-boiling azeotrope

Answer 72

hydrochloric acid-water mixture