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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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