4e

Question 1

when we undergo the aggregation process,, what occurs

Answer 1

u go from 100 free SF molecules to 1 micelle

Question 2

the aggregation process is what

Answer 2

its reversible meaning its dynamic + theres an equilibrium between the SF and the micelles

theres also always an exchange between micelles and surfactants

Question 3

micelles can do what

Answer 3

they can break up and reform

Question 4

name the 2 models that relate 🔺G to CMC

Answer 4

• phase separation model
• closed association model

Question 5

describe the phase separation model

Answer 5

theres 2 phases:
1 = micelles
2 = monomer solution

the two phases are at equilibrium and have the same chemical potential, long.u

Question 6

phase separation model: chemical potential equation

Answer 6

chem potential = standard chem potential + RT ln(a)

u obvs have this for the micelles and then also the monomer solution.

Question 7

for the phase separation model: whats the activity of the micelle phase

Answer 7

micelle is made up of pure substance,, its just the surfactant so a = 1

Question 8

if activity is 1 ,, what does that mean about RT ln(a) of the micelle phase in the phase separation model

Answer 8

it means u can ignore that term bc it will equal 0.

so chemical potential of the micelle phase = standard chemical potential of the micelle phase

Question 9

whats the activity of the monomer solution in the phase separation model

Answer 9

the activivity = the CMC

bc once u reac hthis,, the monomer solution conc remains constant as any additional SF gets put into a micelle.

so a = CMC

Question 10

so 🔺G standard of the micelles is what

Answer 10

standard chem potential final - standard chem potential initial.

= standard chem potential of the micelles - standard chemical potential of the monomer solution.

Question 11

the 2 phases at equilibrium have the same what

Answer 11

they have the same chemical potential ,, so long. u is the same for them both

Question 12

the standard chemical potential of the micelle is what

Answer 12

the standard chemical potential of the monomer + RT ln (a)

so we can subs this into any equation that includes the standard chemical potential of the micelle.

Question 13

🔺G* of the micelle is what

Answer 13

RT ln(A)

RT ln(CMC)

when all things that need cancelling out are cancelled out.

Question 14

describe the closed association model

Answer 14

each step in forming a micelle has a equilibrium constant,, we cant determine every equilibrium constant of every monomer joining to form dimers and so on and so on.

so we assume we can treat all the complex equilibriums as a single process!!!

Question 15

what is nS1 stand for in the closed association model

Answer 15

it stands for n amounts of monomer SF

Question 16

what does Sn stand for in the closed association model

Answer 16

it stands for the micelle.

linke crystal structures whe nthey have like C99,, to tell u how many carbons there are in the structure

Question 17

equilibrium constant for the closed association approach and the equilibrium equation

Answer 17

K

the equation = nS1 <-> SN

so u have

Keq = X[SN]/[X(S1)^N]

conc of the mole fraction of the micelle // conc of mole fraction of the SF monomer

we can put this into the 🔺G = - RT ln(k) equation!!1

Question 18

when we have ln( x/a) how else can we do this

Answer 18

log x - log b

Question 19

so for gibbs equation for the closed association model,, when we put k in,, what does the equation look like

Answer 19

🔺G = - RT ln [ X(Sn) - n RT ln( X(S1) ]

and bc the conc of the monomers is much larger than the conc of the micelle?? we can ignore the first bit

so 🔺G = RT ln( X ( S1) ]

where we use the conc // mole fraction of the monomer solution which is the CMC.

so 🔺G = RT ln ( CMC )

Question 20

when we do the 🔺G = RT ln ( CMC) for the closed association model,, what do we need to make sure

Answer 20

we make sure we use the mole fraction of the CMC

the CMC value must be a mole fraction!!!

Question 21

what is a mole fraction aka how do we find the mole fraction of smt

Answer 21

we do the moles of what we’re interested in / the amount of total moles,, including what we want

Question 22

for X,, aka the mole fraction of the SF ,, what would the mole fraction equation be

Answer 22

mole fraction equation =

moles of SF // moles of water + moles of SF

Question 23

moles of water would be what

Answer 23

1000 / 18

aka the cm3 of a L of water / mr

aka moles = mass / mr

Question 24

for the mole fraction of SF ,, what mole value do we use

Answer 24

we use the mole value of the SF at the CMC!!

Question 25

practice question!!

CMC SF conc = 9x10^-5 moldm-3

T = 25*C

🔺G micelle = whatttttt

Answer 25

• find mole fraction!
  9x10^-5 / (9x10^-5) + ( 1000/18)

= 1.62 x 10^-6

put this into the 🔺G = 8.3145 x 298 x ln( ans)
= -33052 J mol-1
= -33.10 KJ mol-1

Question 26

practice question!!!!

if the equatio nof the line when § is plotted against ln(c) is

y = -0.65x^2 - 14.2x - 3.4
and CMC = 5.2 mM
T = 30

gamma = -1/nrt d§ / d ln(c)
🔺G = RT ln (CMC) find
- gamma CMC (surface excess at cmc)
- A cmc ( area of molecule at cmc)
- 🔺G micelle (free energy change of micellation)

Answer 26

• • gamma CMC (surface excess at cmc) = 2.92 x 10^-6 mM-2

– - A cmc ( area of molecule at cmc) 57 A^2