PHASE EQUILIBRIUM

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PHASE EQUILIBRIUM
They provide us with the knowledge of phase
composition and phase stability as a function of
temperature (T), pressure (P) and composition (C).
one of the most important sources of information
concerning the behavior of elements, compounds
and solutions.
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Chapter outlines
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COMPONENTS
PHASE
PHASE RULE DEGREE OF FREEDOM
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• A chemically and structurally homogeneous portion
  of material
• Separated with other parts of the system

• The mixture of ice and water have two phase
  which is solid and liquid
• The mixture of oxygen gas and nitrogen gas have
  one phase which is gas phase (the system is
  homogen)
• The mixture of oil and water have 2 same
  phase(liquid). Oil and water are not homogen and
  have the boundaries to separate both phase
• CaCO3(s) CaO(s) CO2(g)
• 3 phase (2 solid,1 gas)

PHASE

• Determines the number of independent variables
  needed
• Is the correlation between the number of phase
  (P), components (C), and degree of freedom

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OR
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PHASE RULES
F C P 2
Degree of freedom or the number of
independent variables
The number of phase
2 variables (temperature and pressure)
Number of component
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DEGREE OF FREEDOM (F)
The number of variables that may be changed
independently without causing the appearance of a
new phase or disappearance of an existing phase
UNIVARIANT
TYPES
BIVARIANT
EXAMPLES
Calculate the degree of freedom (F)
The number of components is not always easy to
determine at first glance, and it may require
careful examination of the pyhsical conditions of
the system at equilibrium
F C P 2 2 3 2 1
(univariant)
Means only one variable, either temperature or
pressure can be changed independently
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Standard phase diagram for water (H2O)
Standard phase diagram for carbon dioxide (CO2)
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H2O
Standard phase diagram for one component system
CO2
B
What does it means by 1)AO curve 2)OB curve 3)OC
curve 4)AOB curve 5)BOC curve 6)AOC curve
O
A
?????
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Standard phase diagram for water (H2O)
TA curve known as melting point or freezing
point
Special case !!!!!
Represent the equilibrium between ice and liquid
Has a negative slope
Water as the liquid is denser than the solid (ice
floats on water).
That means that an increase of pressure favors
the formation of liquid and that the melting
point of water falls with increasing pressure.
According to Le Chateliers principle, when
pressure is applied, the reaction shifts in the
direction that can release the stress and cause
ice to melt
This unique properties of water is due to the
network of hydrogen bonding in ice is more
extensive than in liquid
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LEARNING CHECK !!!!!
(d)
(c)
(b)
(a)
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LEARNING CHECK !!!!!
(a)
(b)
(c)
(d)
(e)
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The point O is the triple point for CO2 (at 5.1
atm, -57o C). So, CO2 solid cant changed to
liquid form at 1 atm.
Standard phase diagram for carbon dioxide (CO2)
Critical point
Has a positive slope
So, its shows that the increases of pressure,
will increased the melting point for CO2 solid
O
sublimation
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Raoults law in explaining the effect of
non-volatile solute on vapour pressure of solvent
and its melting and boiling point
Two completely miscible liquid ideal,
non-ideal, positive and negative deviation
Eutectic system and cooling curves
Composition diagram vs boiling point composition
for ideal, non-ideal, negative n positive
deviation
Fractional distillation and azeotropic system
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Vapour pressure of a liquid
Vapour pressure increases with increasing
temperature due to its KE
When a liquid evaporates in a closed vessel, its
gaseous molecules formed above the liquid have
high KE and exert a vapour pressure.
The molecules collide with the pinston and push
the pinston upward
sublimation
Microscopic equilibrium between gas and liquid.
Note that the rate of evaporation of the liquid
is equal to the rate of condensation of the gas.
Microscopic equilibrium between gas and solid.
Note that the rate of evaporation of the solid is
equal to the rate of condensation of the gas.
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Vapour pressure of a volatile liquid
Volatile liquid is a liquid that can easily
evaporate at one atmospheric pressure and room
temperature
Molecules of volatile liq escape the liquid phase
into gaseous phase.(KE)
A volatile liquid has a strong tendency to
vapourize or evaporate into vapour, creating high
vapour pressure.
On contrary a less volatile liquid has low vapour
pressure because of lower tendency to vapourize
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Factor that affect Vapour pressure
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ethyl ether (C4H10O)Pvapor (25oC) 520 torr

• Types of Molecules the types of molecules that
  make up a solid or liquid determine its vapor
  pressure. If the intermolecular forces between
  molecules are
• relatively strong, the vapor pressure will be
  relatively low.
• relatively weak, the vapor pressure will be
  relatively high.

ethyl alcohol (C2H6O)Pvapor (25oC) 75 torr
Low Temperature
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Temperature at a higher temperature, more
molecules have enough energy to escape from the
liquid or solid. At a lower temperature, fewer
molecules have sufficient energy to escape from
the liquid or solid.
High Temperature
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• 3 types
• Complete Miscible liquid
• Half miscible liquid
• Immiscible liquid

Methanol and ethanol
Liquid solution in liquid
ether and water
Oil and water
Ideal solution- mostly involve the substance that
have similar physicochemical properties. Ex
MeOH/EtOH, benzene/toluene, n-hexane/n-heptane
Complete Miscible liquid

• 2 types of complete miscible liquid which is
  ideal and non-ideal solution
• An ideal solution is a solution that obeys
  Raoults law and non-ideal solution disobey.
• A solution is a ideal solution when
• The intermolecular attractions between the
  mixture of same molecule with the the mixture of
  different molecule are equal.
• The volume of the mixture are the total volume of
  both liquid (volume of liquid A add with volume
  of liquid B)
• No heat changes (no endo-exothermic process)
• Obeys Raoults law

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Raoults law ideal solution

• Relationship between vapour pressure of a solvent
  and its mole fraction
• States the vapour pressure of the solute
  containing solution (PA) is equal to the mole
  fraction of the solvent (XA) times the vapour
  pressure of the pure solvent (Po A)

PA XA Po A Psolution Xsolvent Po solvent
PT PA P B _at_ Ptotal XA PoA XB PoB
EXAMPLE !!!!!
A solution is prepared by adding 2.0 mole of
glucose in 15.0 mole of water at 25 oC. The
vapour pressure of pure water at 25 oC is 23.76
mmHg. Calculate the vapour pressure of the
solution at 25 oC
Psolution Xsolvent Po solvent The mole
fraction XA nA / nt 15.0 /17.0
0.88 Therefore, Psolution 0.88 x 23.76 mmHg
20.96 mmHg
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EXAMPLE !!!!!
At 25 oC the vapour pressure of pure benzene and
toluene are 93.4 mmHg and 26.9 mmHg. If the
mixture contains 60.0g of benzene and 40.0 g of
toluene, calculate the vapour pressure of this
solution
PT PA P B _at_ Ptotal XA PoA XB PoB
Calculate the number of moles for benzene and
toluene n of benzene PA P B 60/78 0.77
mole n of toluene PA P B 40/92 0.43 mole
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VAPOUR PRESSURE/ COMPOSITION DIAGRAM
BOILING POINT/ COMPOSITION DIAGRAM
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Vapour pressure/composition diagram(ideal
solution)

• There is actually no such thing as an ideal
  mixture! However, some liquid mixtures get fairly
  close to being ideal. These are mixtures of two
  very closely similar substances. Commonly quoted
  examples include
• hexane and heptane
• benzene and methylbenzene
• propan-1-ol and propan-2-ol

Pure mixture vapour pressure
Notice that the vapour pressure of pure B is
higher than that of pure A. That means that
molecules B must break away more easily than of
A. B is the more volatile liquid.
Pure vapour pressure
Total vapour pressure of the mixture
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Boiling point/composition diagram
We'll start with the boiling points of pure A and
B.B has the higher vapour pressure. That means
that it will have the lower boiling point.
The diagram just shows what happens if you boil a
particular mixture of A and B. Notice that the
vapour over the top of the boiling liquid has a
composition which is much richer in B - the more
volatile component.
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EXAMPLE !!!!!
Which vapour sample rich at this point?
composition
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Vapour composition of a negative deviation
solution

• Involves the intermolecular forces between
  molecules in solution are stronger than those in
  pure liquid
• Therefore, vapour pressure of the solution is
  lower than vapour pressure of its components or
  pure liquid.
• Example

• SO,the molecules in the solution have lower
  tendency to escape into vapour phase.
• Therefore the process is EXOTHERMIC

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Nitric acid and water form mixtures in which
particles break away to form the vapour with much
more difficulty than in either of the pure
liquids.
Azeotrope
That means that mixtures of nitric acid and water
can have boiling points higher than either of the
pure liquids because it needs extra heat to break
the stronger attractions in the mixture.
In the case of mixtures of nitric acid and water,
there is a maximum boiling point of 120.5C when
the mixture contains 68 by mass of nitric acid.
That compares with the boiling point of pure
nitric acid at 86C, and water at 100C.
Notice the much bigger difference this time due
to the presence of the new ionic interactions
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USING THE DIAGRAM
As the acid loses water, it becomes more
concentrated. Its concentration gradually
increases until it gets to 68 by mass of nitric
acid. At that point, the vapour produced has
exactly the same concentration as the liquid,
because the two curves meet.
Distilling dilute nitric acid Start with a dilute
solution of nitric acid with a composition of
C1and trace through what happens.
You produce a constant boiling mixture (or
azeotropic mixture or azeotrope). If you distil
dilute nitric acid, that's what you will
eventually be left with in the distillation
flask. You can't produce pure nitric acid from
the dilute acid by distilling it.
The vapour produced is richer in water than the
original acid. If you condense the vapour and
reboil it, the new vapour is even richer in
water. Fractional distillation of dilute nitric
acid will enable you to collect pure water from
the top of the fractionating column.
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Distilling nitric acid more concentrated than 68
by mass This time you are starting with a
concentration C2 to the right of the azeotropic
mixture.
The vapour formed is richer in nitric acid. If
you condense and reboil this, you will get a
still richer vapour. If you continue to do this
all the way up the fractionating column, you can
get pure nitric acid out of the top.
As far as the liquid in the distillation flask is
concerned, it is gradually losing nitric acid.
Its concentration drifts down towards the
azeotropic composition. Once it reaches that,
there can't be any further change, because it
then boils to give a vapour with the same
composition as the liquid.
Distilling a nitric acid / water mixture
containing more than 68 by mass of nitric acid
gives you pure nitric acid from the top of the
fractionating column and the azeotropic mixture
left in the distillation flask.
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Vapour composition of a positive deviation
solution
Formed when the intermolecular forces between
molecules in the mixture are weaker than those in
pure liquids.
The solution has a greater tendency to evaporate
or escape into vapour
Vapour pressure of the solution is higher than
expected
The process is endothermic
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A large positive deviation from Raoult's Law
produces a vapour pressure curve with a maximum
value at some composition other than pure A or B.
If a mixture has a high vapour pressure it means
that it will have a low boiling point
The molecules are escaping easily and you won't
have to heat the mixture much to overcome the
intermolecular attractions completely.
The implication of this is that the boiling point
/ composition curve will have a minimum value
lower than the boiling points of either A or B.
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USING THE DIAGRAM
Suppose you are going to distil a mixture of
ethanol and water with composition C1 as shown on
the next diagram. It will boil at a temperature
given by the liquid curve and produce a vapour
with composition C2.
When that vapour condenses it will, of course,
still have the composition C2. If you reboil
that, it will produce a new vapour with
composition C3.
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This particular mixture of ethanol and water
boils as if it were a pure liquid. It has a
constant boiling point, and the vapour
composition is exactly the same as the liquid.
AZEOTROPE
It is known as a constant boiling mixture or
an azeotropic mixture or an azeotrope.
SUMMARISE

• Distilling a mixture of ethanol containing less
  than 95.6 of ethanol by mass lets you collect
• A distillate containing 95.6 of ethanol in the
  collecting flask (provided you are careful with
  the temperature control, and the fractionating
  column is long enough
• Pure water in the boiling flask.

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Typical fractional distillation in the lab
the thermometer bulb is placed exactly at the
outlet from the fractionating column
to give the maximum possible surface area for
vapour to condense on
Some fractionating columns have spikes of glass
sticking out from the sides which serve the same
purpose
In some cases, where you are collecting a liquid
with a very low boiling point, you may need to
surround the collecting flask with a beaker of
cold water or ice.
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Relating what happens in the fractionating column
to the phase diagram
Boil a mixture with composition C1.
Which compound that rich at this point? What
phase?
Which compound that rich at this point? What phase
The vapour over the top of the boiling liquid
will be richer in the more volatile component,
and will have the composition C2.
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Which compound that rich at this point? What
phase?
Each time the vapour condenses to a liquid, this
liquid will start to trickle back down the column
where it will be reboiled by up-coming hot
vapour. Each time this happens the new vapour
will be richer in the more volatile component.
The aim is to balance the temperature of the
column so that by the time vapour reaches the top
after huge numbers of condensing and reboiling
operations, it consists only of the more volatile
component - in this case, B.
The boiling points of the two liquids. The closer
they are together, the longer the column has to
be.
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what is the point of the packing in the column?

• To make the boiling-condensing-reboiling process
  as effective as possible, it has to happen over
  and over again.
• By having a lot of surface area inside the
  column, you aim to have the maximum possible
  contact between the liquid trickling down and the
  hot vapour rising.

• If you didn't have the packing, the liquid would
  all be on the sides of the condenser, while most
  of the vapour would be going up the middle and
  never come into contact with it.

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BOILING POINT is the temperature at which its
vapour pressure equals the external pressure
WHY??
Boiling point of pure solvent
Boiling point solvent is higher than boiling
point of solution
?Tb Tb - T ob
Boiling point of solution
Boiling point elevation
?Tb is proportional to molality of solute in
the solution, so.
?Tb Kb m
The molal boiling point elevation constant with
unit oC/m or oC kg/mol
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EXAMPLES
What is the boiling point elevation when 11.4 g
of ammonia (NH3) is dissolved in 200. g of water?
Kb for water is 0.52 C/m.

• Determine molality of 11.4 g of ammonia in 200. g
  of water
• 11.4 g / 17.031 g/mol 0.6693676 mol
• 0.6693676 mol / 0.200 kg 3.3468 m

2) Determine bp elevation ?t Kb m ?t (0.52
C/m) (3.3468 m) ?t 1.74 C
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EXAMPLES
Calculating Molecular Mass (Formula Weight) of
Solute 1.15g of an unknown, nonvolatile compound
raises the boiling point of 75.0g benzene (C6H6)
by 0.275oC. Calculate the molecular mass
(formula weight) of the unknown
compound. Calculate the molality of solute
particles m  ?Tb  Kb ?Tb  0.275oC Kb 
2.53oCm-1 (from table above) m  0.275 2.53
0.109m Calculate the moles of solute
present molality moles solute kg
solvent n(solute)  m x kg solvent 0.109 x
75.0 x 10-3  8.175 x 10-3 mol Calculate the
molecular mass (formula weight) of the
solute n(solute) mass(solute)
MM(solute) MM(solute) mass(solute) n(solute)
1.15 8.175 x 10-3  141 g/mol
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FREEZING POINT DEPRESSION is the temperature at
which solid begins to appear in liquid or solution
Boiling point of solution
?Tf T of - Tf
T of gt Tf
Boiling point of pure solution
?Tf is proportional to molality of solute in
the solution, so.
?Tf Kf m
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• the boiling point of the solvent in a solution is
  higher than that of the pure solvent

• the freezing point (melting point) of the solvent
  in a solution is lower than that of the pure
  solvent.

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Learning check !!!!!!
Automobile antifreeze is ethylene glycol, C2H6O2.
It is a non-electrolyte. If a radiator contains
40.0 antifreeze and 60.0 water, by mass, what
is the freezing point of the solution in the
radiator? The normal freezing point for water is
0.0 C and Kf is 1.86 C mol/kg.
Find the molality of the solution. The mass of
the solvent is 0.0600 kg and the formula weight
of the solute is 62.066 g/mol.                    
                              Use the
freezing point depression formula                 
                                                
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Its the BONUS TIME AND YOUR HAPPY HOUR. THIS IS
YOUR HOMEWORKS TO FIND ABOUT EUTECTIC MIXTURE AND
COOLING CURVES
EUTECTIC MIXTURE AND COOLING CURVES
YOU HAVE TO MAKE A SHORT NOTES ON THIS SUBTOPIC
AND SUBMIT IT TO YOUR KAWAII LECTURER
GOOD LUCK GUYS