Simple Mixtures

Question 1

(T/F): For a system with more than one component, we can define molar quantity for each component.

Answer 1

False. We can define PARTIAL molar quantity for each component

Question 2

Formula for partial molar volume.

Answer 2

Vi = ( change V/ change ni) at constant T, P, nj

Question 3

Define partial molar volume

Answer 3

Change in volume of mixture when small amount of i is added, holding other variables constant

Question 4

Illustrate partial molar volume through binary system of water and ethanol.

Answer 4

Adding 1mol of water to 1 vat of water will result of 18mL increase in volume which is same as the molar volume of pure water

Adding 1 mol of ethanol to same vat of water will result to 54 mL increase in volume which is less than the molar volume of pure ethanol (58 mL)

The partial molar volume of ethanol is 54 mL

Question 5

Molar quantities are not ____ but partial molar quantities are.

Answer 5

explicitly additive

Question 6

Change in molar volume (dV) is equal to?

Answer 6

summation of product of partial molar volume and change in the number of moles of each component

dV = E Vi dni

Question 7

Define chemical potential.

It is the measure of?

Answer 7

In a mixture, the chemical potential is the change in Gibbs free energy (spontaneity) of the system when small amounts of i is added to it, with other variables held constant

It is the measure of tendency of substances to transform or escape.

Question 8

The chemical potential must be ___ throughout the system because of its ___ property

Answer 8

the same; intensive

Question 9

Chemical potential is also known as the?

Answer 9

Molar Gibbs energy

Question 10

In a single component with more than one phases, the change in Gibbs free energy is equal to?

Answer 10

Summation of product of chemical potential and change in number of moles of each phases.

Question 11

In an isolated system with two phases, change in G is?

Answer 11

dG =[chem po (a)-chem po (b)] dni (a)

Question 12

What will happen to amount of i in phase b (and the sign) if the chemical potential of i in phase a is greater than the phase b? What is the direction of i?

Answer 12

increase; positive

moves from phase a toward phase b
(from higher chemical potential to lower)

Question 13

(T/F). Movement of amount of i will continue until dG becomes constant.

Answer 13

False. until dG becomes zero.

Question 14

(molar) Gibbs free energy of an ideal gas with temperature and pressure

Answer 14

dG = V dP - S dT

dGm = Vm dP - Sm dT

Question 15

Chemical potential of ideal gas

Answer 15

m = mu (T) + RT ln P

chem po = stand. chem po at temp T + RT ln P

Question 16

Ideal solution is defined as solution that obeys ____ over the ____.

Answer 16

Raoult’s Law; entire range of concentration.

Question 17

What is Raoult’s Law?

Answer 17

Vapor pressure over a solution is dependent on the mole fraction of the volatile component in the solution.

Lowering vapor pressure of a volatile liquid due to presence of solute

Question 18

The vapor pressure exerted by a solution in which the solvent is volatile and solute is involatile is? ( in terms of molar fraction of solvent and solute)

Answer 18

Pi = xi Pi*

vapor pressure by solution = molar fraction of volatile solvent * vapor pressure by pure solvent

In terms of involatile solute:

Pi = Pi* (1-xj)

Question 19

Vapor pressure of the volatile component in a solution is always ___ its vapor pressure as a pure liquid.

Answer 19

less than

Question 20

What is the chemical potential of a volatile component in solution?

Answer 20

mu i (sol’n) = mu i* + RT ln xi

chemical potential of solution = chemical potential of pure liquid + RT ln molar fraction

Question 21

Properties of solution that depend only on the amount of involatile solute in solution

Answer 21

Colligative Properties

Question 22

Colligative properties do not depend on the nature of solute but only on?

… however?

Answer 22

the number of solute molecules relative to the total number of molecules present (solute mole fraction)

Vapor pressure decrease depends on solvent mole fraction.

Hence, colligative properties actually depend on the relative amount of volatile component in the solution

Question 23

Form of Gibbs-Helmholtz equation for melting point depression

Answer 23

d(∆G/T)/dT = -∆H/T^2

∆G=T∆H-∆S

Question 24

Mathematical expression for melting point depression and what it implies?

Answer 24

1/T = 1/T0 - R ln xi / ∆Hfusion

T0 = melting point of pure solvent
T = melting point of solution

: mp of solution is always less than mp of pure solvent

Question 25

MP expression when solution is very dilute

Answer 25

T = T0 - Kf m

Kf = cryoscopic constant
Kf = -MRT0^2 / ∆Hfusion

Question 26

BP elevation expression and what it implies?

Answer 26

1/T = 1/T0 + R ln xi / ∆Hvaporization

T0 = bp of pure solvent
T = bp of solution

: BP of solution is always greater than BP of pure solvent

Question 27

BP expression in terms of molal concentration of solute

Answer 27

T = T0 + Kb m

Kb = MRT0^2 / ∆Hvaporization

Question 28

If a pure solvent is separated from its solution by a membrane permeable only to the solvent, _____

Answer 28

the solvent molecules will move through the membrane to establish equilibrium

Question 29

tendency (chemical potential) is for matter to move from

Answer 29

higher chem po to lower chem po

Question 30

Pressure required to stop or reverse the movement of matter

Answer 30

osmotic pressure

Question 31

To achieve equilibrium, the solvent must exert ___ as that of solvent

Answer 31

same pressure

Question 32

molar fraction, xj = ?

Answer 32

nj / nj + ni

Question 33

osmotic pressure in terms of molar concentration of solute

Answer 33

osmotic pressure = cj RT

cj = nj / Vsolution