Chemical potential and collegiative properties

Question 1

chemical potential at equilibrium

Answer 1

mu1 = mu2

Question 2

relationship between mu and G

Answer 2

mu is a molar form of Gibbs energy

Question 3

General change in pressure with temperature for a phase change

Answer 3

dp/dT = dHtrans/dTtrans

Question 4

Fusion pressure and temperature changes

Answer 4

p2 - p1 = dH/dV(ln(T2/T1))

Question 5

Evaporation temperature and pressure changes

Answer 5

ln(p2/p1) = -dH/R(1/T2 - 1/T1)

Question 6

sublimation temperature and pressure changes

Answer 6

ln(p2/p1) = -dH/R(1/T2 - 1/T1)

Question 7

What is Gibbs energy of a system the sum of

Answer 7

The sum of the partial molar chemical potentials of each species in the system

Question 8

How does Gibbs vary with pressure, temperature and composition

Answer 8

dG = Vdp - SdT + sum(mun)
mun = partial molar chemical potential

Question 9

what is Xr or Xb etc

Answer 9

molar fraction of a species

Question 10

entropy of mixing

Answer 10

dS = -nR[XrlnXr + XblnXb]

Question 11

Gibbs of mixing

Answer 11

dG = nRT[XrlnXr + XblnXb]

Question 12

Chemical potential and its relationship with vapour pressure

Answer 12

The phase change between liquid and gas is in equilibrium and so, the chemical potential of the gas and liquid are equal

Question 13

Chemical potential of a mixture

Answer 13

mu = mu* + RTln(pa/pa )
mu = mu of the pure species
pa* = pressure of the pure species

Question 14

Raoult’s law, conditions and assumptions

Answer 14

pa = Xapa*
for concentrated solutions or dilute solutions with similar solvent and solute properties as the solute is assume to behave ideally when surrounded by other solute molecules
* means pure solution

Question 15

Raoult’s law and chemical potential

Answer 15

Xa = pa/pa* therefore

mu = mu* + RTln(Xa)

Question 16

Henry’s law, conditions and assumptions

Answer 16

pa = khXa
for dilute solution as the solute is assumed to act ideally when surrounded by solvent molecules

Question 17

osmotic pressure

Answer 17

the pressure required to prevent osmosis

Question 18

osmotic pressure equation

Answer 18

O = njRT/Vm
nj = number of moles of solute
Vm = partial molar volume

Question 19

osmotic pressure of an ideal solution

Answer 19

Vm = molar volume
therefore
O = cRT
c = molar conc of solute in molm-3

Question 20

osmometer calculation

Answer 20

p = rgh
r = density
g = acceleration due to gravity
h = height in m

Question 21

Change in the melting or boiling point temperature of a mixture

Answer 21

dT = (RT^2/dH)Xb

T = temperature of pure fusion or vapourisation
dH = enthalpy change of pure fusion or vaporisation
Xb = molar fraction of the original

Question 22

Units for the change in boiling or freezing temperatures of a mixture

Answer 22

dH is in Jmol-1
T is in kelvin

Question 23

What makes ice slippery?

Answer 23

A mode predicts that the upper layers of ice are not true solids, but instead partial liquids. This is maintained even at temperatures well below freezing point which allows for ice to be slippery both at these temperatures, and when very little pressure is applied

Question 24

enthalpy change of mixing

Answer 24

0 kJmol-1

Question 25

What does it mean practically if mixing is endo or exothermic

Answer 25

If exothermic, the reaction with be spontaneous and energetic. If endothermic, the driving force becomes entropy and if it is not large enough, the species are immiscible

Question 26

Deviations from Raoult’s law

Answer 26

Positive: if A-B interactions are weak and species prefer to be separated
Negative: is A-B interactions are strong and species prefer to be mixed