Solutions and Mixtures

Question 1

Gibbs Phase Rule? And what do each of the terms represent?

Answer 1

F=C-P+2
F: Degrees of freedom - for a point F=0, for a line F=1 and for an area, F=2. IN TEMP PRESSURE GRAPHS.
C: No. chemical components (for a pure system this is 1).
P: No. phases (3 for a point, 2 for a line, 1 for an area)

Question 2

What do you know about the chemical potential of two phases of a pure system?

Answer 2

for a pure system of phases (l) and (ll),

𝜇(𝐼) = 𝜇(𝐼𝐼)

Question 3

As the chemical potential of two phases in a pure system is equal, how can you adapt the change in enthalpy?

Answer 3

Δℎ = 𝑇Δs

Question 4

How can you get enthalpy change from a pressure temperature phase diagram?

Answer 4

Clapeyron equation.

𝑑𝑃/𝑑𝑇=Δ𝑠/Δ𝑣=Δℎ/TΔv

Question 5

How can you get enthalpy change from the liquid/gas or solid/gas phase boundaries?

Answer 5

Clausius-Clapeyron equation

𝑑𝑃/𝑑𝑇=PΔ𝑠/𝑅𝑇=𝑃Δℎ/𝑅𝑇^2

Question 6

The linearized Clausius-Clapeyron plot makes a straight line to use. What are the axis?

Answer 6

y axis: lnP

x axis: 1/T

Question 7

The linearized Clausius-Clapeyron plot makes a straight line to use. What is the equation for its gradient?

Answer 7

𝑑 ln 𝑃/𝑑(1/𝑇)= −Δℎ/R

Question 8

The linearized Clausius-Clapeyron plot makes a straight line to use. What phase boundary does the equation only work for?

Answer 8

anything that is a phase boundary with gas. Can be the liquid/gas or the solid/gas.

Question 9

What is headspace measurment?

Answer 9

measure vapour pressure

Question 10

In a mixture, what is the equation for a(i), the activity?

What are each of the terms?

Answer 10

𝑎𝑖 =𝑃(𝑖)/𝑃(𝑖𝑜)
(make sure you know correct way it should look, formatting here is wrong)
a: activity - a measure of affinities of solute and solvent to the solution compared to their pure systems.
p(i) : Partial vapour pressures of the solution.
p(io) : Vapour pressures of the pure system

Question 11

Ideal gas law?

Answer 11

pV=nRT
p- Pa
V- m3
n- mols
R-JK-1mol-1
T- K

Question 12

Activity Coefficient?

Answer 12

𝛾(𝑖) =𝑎(𝑖)/𝑥(i)

Question 13

If 𝛾𝑖 > 1, what does this show?

How will it look on a pressure/composition graph?

Answer 13

weaker affinity for solution.
+ve deviation from ideality.
on a graph will have a sad face upwards curve from the ideal line (a straight line)

Question 14

If 𝛾𝑖 < 1, what does this show?

How will it look on a pressure/composition graph?

Answer 14

stronger affinity for solution.
-ve deviation from ideality.
on a graph will have a smiley face downwards curve from the ideal line (a straight line)

Question 15

If 𝛾𝑖 = 1, what does this show?

How will it look on a pressure/composition graph?

Answer 15

ideal solution

straight lines

Question 16

What is a perfect solution?

Answer 16

one that is ideal over an entire concentration

Question 17

For an ideal solution, what does the activity equal? (when the solute is in approximately same concentration as solvent)

Answer 17

𝑎 = 𝑥 (the mol fraction) as 𝛾 accounts for deviations from ideality.

Question 18

What does a linear composition/pressure plot show?

Answer 18

ideal solution

Question 19

When the solute is dilute, what can be approximated about the solvent?
Raoults law

Answer 19

When the solute conc is v small, both solvent and solute start to behave ideally as molecular interactions become negligible. Vapour pressure of the solvent P is proportional to the mol. fraction of the solvent x.
Therefore:
a ≅ x (x is mol fraction solubility)

Question 20

When the solute is very dilute, what can be approximated about the solute?
Henrys law

Answer 20

P = kx
k= henrys law constant (sometimes has a subscript H)
strictly applicable for dilute solutes.

Question 21

The equation for boiling point elevation by dilute solutes?

Answer 21

Δ𝑇(𝑏) = 𝐾(𝑏)𝑚(2)
𝑚2: solute molality
𝐾𝑏: ebullioscopic constant (of the solvent)

Question 22

The equation for freezing point depression by dilute solutes?

Answer 22

−𝛥𝑇(𝑓) = 𝐾(𝑓) 𝑚(2)
𝑚2: solute molality
𝐾𝑏: cryoscopic constant

Question 23

What is molality?

Answer 23

mole of solute in a kg of solvent

Question 24

What is molarity?

Answer 24

mole of solute in a litre of solution

Question 25

What is the equation for osmotic pressure?

Answer 25

𝛱 = 𝑅𝑇𝑐(2)
where c(2) is molarity