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5.2 LIQUIDS
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Properties of liquids
Explain :
- vaporisation process
- condensation process
Define vapour pressure and boiling point
Relate :
- intermolecular forces to vapourpressure
- vapour pressure to boiling point
Based on KineticMolecular Theory& IntermolecularForces
Objective:
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Comparison of Gas, Liquids & SolidsComparison of Gas, Liquids & Solids
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properties of Liquids
properties of Liquids
1. Shape NO definite shapedefinite shape..
Takes the shape of the container.
The intermolecular forces are NOT
strong enough to hold the particles
rigidly in place.
Molecules can slide past each other.
thus, a liquid flows to fit the shapeliquid flows to fit the shape of its
container.
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2. Volume has a definite volumedefinite volume .
intermolecular forces are strong enough
to control the movement of liquid
molecules.
thus, a liquidliquidisconfined to a certainconfined to a certain
volumevolume
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3. Compressibility3. Comp
ressibility
Incompressible.
The molecules are packed closely
together
there are very little empty spaces
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4. Diffusion4. Diffusion
Can flow readily but slower than gasgas
Liquid molecules are arranged more
closely than gas
lower kinetic energylower kinetic energy than gases
stronger intermolecular attractive forcesstronger intermolecular attractive forces
restrict liquid to diffuse.
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Surface TensionSurface Tension
Water beads on nonwaxed and waxed surface
Is a phenomenon that arises due to the inward pull
on the molecules at the surface.
Is a phenomenon that arises due to the inward pull
on the molecules at the surface.
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Surface Tension,Intermolecular forces
Molecules within a liquid are
pulled by intermolecular forces
EQUALLY in all directions.
However, molecules at the
surface are pulled downwards and
sideways by other molecules BUT
NOT UPWARD away from thesurface.
UNBALANCED
INTERMOLECULAR FORCES
pull the molecules INTOtheliquid and cause the surface to
TIGHTEN like an ELASTIC FILM.
The stronger the intermolecularstronger the intermolecular forces,
the higher the surface tensionhigher the surface tension
The stronger the intermolecularstronger the intermolecular forces,
the higher the surface tensionhigher the surface tension9
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Decreases with increase in temperature.Decreases with increase in temperature.
- Kinetic energy of molecules increases- Kinetic energy of molecules increases
- Molecules move faster- Molecules move faster- Intermolecular forces weaken- Intermolecular forces weaken
Surface TensionSurface Tension
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6. Viscosity6. Viscosity
is a measure of the
liquids resistanceresistance toto
flowflow the greater thegreater the
viscosityviscosity, the
slowerslower it flows.it flows.
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The intermolecular forces create aninternal friction (cohesive forces) that
restrict the liquid to flow freely.
Bigger size or molecular masshigherviscosity
Stronger intermolecular forceshigher
viscosity Temperature increasesviscosity
decreases
ViscosityViscosity
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VaporisationVaporisation
a process in which liquid changes to gasliquid changes to gas
molecules move more freely
some molecules at the surface have
higher kinetic energies
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VaporisationVaporisation
the molecules will
leave as vapour
when the kinetic
energy is sufficient
GREATER than the
intermolecular
forces.
( vaporisation)
vaporisation 14
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CONDENSATIONCONDENSATION
The vapour molecules
lose energy during
collisions
Return or trapped back
to the liquid
(condensation)condensation
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VAPOUR PRESSUREVAPOUR PRESSURE
The vapour molecules collide
each other and with the walls
of container and therebyexerts pressure.
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When the rate of evaporation and
condensation become equal, a
state ofdynamic equilibrium isreached.
The pressure exerted at this stateis called equilibrium vapour
pressure of the liquid.
The term vapour pressure of liquidis normally referred as equilibrium
vapour pressure.
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The vapour pressure of a liquid is the pressure exerted bythe vapour molecules above the surface of the liquid whenit is in dynamic equilibrium with a liquid at a constanttemperature.
Vapour pressure is independent ofvolume orsurfacearea of liquid as long there is some liquid present.
Factors affecting vapour pressure:
Strength/type of attractive forces between liquid molecules temperature molecular mass size of liquid molecules
VAPOUR PRESSUREVAPOUR PRESSURE
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When a liquid evaporates, its gaseous molecules exert a
vapour pressure.
vacuum
Vapour pressure is measured
when a dynamic equilibrium
exist between condensation
and vaporisation.
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Vapour pressure increases with temperature.
TEMPERATURE
200 K
300 K
400 K
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Vapour pressure increases with temperature.
TEMPERATURE
200 K
300 K
400 K
LOW TEMPERATURE LOW VAPOUR PRESSURE21
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Vapour pressure increases with temperature.
TEMPERATURE
200 K
300 K
400 K
HIGH TEMPERATURE HIGH VAPOUR PRESSURE22
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evaporation boiling
The change of state
of a liquid into aliquid into a
vapourvapour occuring at theat the
surfacesurface of a liquid atat
any temperatures andany temperatures andpressurespressures
The change of state of a
liquid into a vapourliquid into a vapour occuring at
the surface and on the innerinner
part of the liquidpart of the liquid at a certaincertain
temperaturetemperature of which thevapour pressure is equal to theequal to the
atmospheric pressureatmospheric pressure
Vaporisation
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Boiling point of a liquid is defined as the
temperature at which the vapour pressure of the
liquid equals the external atmospheric pressure.
Boiling occurs at a specific T and P T remains constant even though heat is still
supplied.
Normal boiling point is the temperature at which a
liquid boils when the external pressure is 1 atm.
BOILINGBOILING
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Increase in vapour
pressure with temperature
Vapour pressure curve
Normal
boiling point
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Factors affecting rate of evaporation:
Surface area
Evaporation is easier when the surface area
is bigger.
Bigger chance to escape from the surface.
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Temperature
At higher T, average Ek of molecules increases Easier to overcome the intermolecular forces
More molecules escape as vapour
Rate of evaporation increases
Intermolecular attractive forces
Weak intermolecular forces, easier to escape fromthe surface (more volatile).
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Size or molecular mass
The bigger the size, the bigger is the
molecular mass. The stronger the intermolecular forces
Molecules difficult to escape from surface
Rate of evaporation decreases.
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i) Purity
The boiling point of a liquid is elevated(increased)in the presence of impurities.
ii) Atmospheric Pressure
The higher the atmospheric pressure, the higherthe boiling point of a liquid. More heat is needed
so that the molecules have more kinetic energyto vaporise and to reach vapour pressure equal toexternal atmospheric pressure.
Factors affecting boiling point
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iii) Intermolecular forces
Liquids with stronger intermolecular
attraction forces will have lower vapourpressure and higherboiling points.
More energy is needed to overcome the
intermolecular attractive forces to vaporiseand to reach vapour pressure equal to the
external atmospheric pressure.
Factors affecting boiling point
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Relationship between intermolecular force,
vapour pressure and boiling point
If the intermolecularattractive forces are weak,
the liquid molecules can vapourise easily.
Therefore, the vapour pressure is high.
less energy is needed for its vapour to achieve the
external atmospheric pressure.
boiling point is lower.
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OBJECTIVES
1) Properties of solids
2) Describe phase change
3) Types of crystalline solids
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particles are arranged very closelyarranged very closely
together, little empty spaces
has strong forcesstrong forces between the particlesparticles can onlyonly vibrate and rotatevibrate and rotate
about fixed position, cannot move freely
has definite shape and volume
has high densities
are incompressible
Properties of SolidProperties of Solid
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gas liquid
solid 35
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particles = atoms/ions/molecules
Interparticle forces NOT intermolecular
forces
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PHASE CHANGE
solid gas
liquid
meltin
g
freez
ing
sublimation
deposition
vaporisation
condensation
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when a liquid is cooled:
kinetic energy of liquid particles
decreases
the liquid particles vibrate at a
slower rate
the liquid particles move closer to
each other
at its freezing point, the
interparticle forces
Freezing (Solidification)Freezing (Solidification) Liquid solid
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When a solid substance is heated : kinetic energy of solid particles increases
particles vibrate more quickly and energetically
at its melting point, particles have enough energyto overcome the interparticle forces
OR the vibrations disrupt the orderly solid structure.
particles slip past one another, solid loses its
definite shape and converted to liquid. the solid melts
Melting (FusION)Melting (FusION) solid liquid
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When a solid substance is heated :
kinetic energy of solid particles increases
abruptly
particles vibrate very vigorously that they
straight away change to the disorder
arrangement of gas
the solid sublimes to gas withoutgoing through liquid phase
SublimationSublimationsolid gas
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Deposition
If a gas is supercooled, kinetic energy of gas particles decreases
abruptly
particles move very closely to each otherand straight away change to the orderly
arrangement of solid
the gas changes to solidwithout go through the liquid
phase
gas solid
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Types of solid:
Amorphous and Crystalline solids
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Yellow P
Red P
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amorphous solidcrystalline solid
No regular 3-D
arrangement of
particles
formed when asaturated liquid is
cooled rapidlycooled rapidly
example : glass
plastic material
charcoal
atoms, ions or
molecules are occupy
specific positions
formed when a
saturated liquid is
cooled slowlycooled slowly
example :
ice,
sugar,
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SOLIDMETALLICSOLID(Na, Gold)
GIANT COVALENTSOLID
(Diamond, Graphite)
MOLECULARCOVALENTSOLID
(Solid CO2)
IONIC SOLID(NaCl,CsCl)
TYPES OFCRYSTALLINESOLID
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molecular covalent solidsmolecular covalent solids composed of moleculesmolecules/atoms held
together by van der Waals forcesvan der Waals forces
examples : P4, S8, iodine, dry ice(Solid
CO2),
Types of Crystalline SolidTypes of Crystalline Solid
SULPHUR
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giantgiantcovalent solidscovalent solids very large atoms/moleculeslarge atoms/molecules
composed of atoms linked together
by a network ofcovalent bondscovalent bonds
examples : diamond, graphite,
quartz(SiO2)
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graphite
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Fig. 2.15b, p.84
diamond
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GIANT COVALENT SOLIDGIANT COVALENT SOLID
DiamondDiamond
GraphiteGraphite
Quartz, SiOQuartz, SiO22
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ionic solidsionic solids
consist of ions (cation & anion) held
together by ionic bonds/ electrostaticionic bonds/ electrostatic
forcesforces
example : NaCl , KI
Na+ Cl- Na+ Cl-
Na+Cl- Na+Cl-
Na+ Cl- Na+ Cl-
Arrangement ofions
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IONIC SOLIDS
Azurite, a copper
carbonate
Iron pyrite, a sulphideOrpiment,
arsenic sulphide
Potasiumnitrate crystal52
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metallic solidsmetallic solids
close packed structure
composed of atoms of the same metalatoms of the same metal
linkedtogether by metallic bondmetallic bond
examples : all metallic elements : Na,
Mg, Fe Na+
Na+
Na+
Na+
Na+Na+ Na+Na+
Na+ Na+ Na+ Na+
Na+
Na+
Na+Na+
Na+ Na+
Na+ Na+ Na+ Na+ Na+ Na+
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METALLIC SOLIDS
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