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8/19/2019 5.2 Liquid State Editted Lec
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8/19/2019 5.2 Liquid State Editted Lec
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Explain the properties of liquids : shape, volume, surfacetension, viscosity, compressibility and difussion.
Explain :
- vaporisation process
- condensation process
Define vapour pressure and boiling pointRelate :
- intermolecular forces to vapour pressure
- vapour pressure to boilin point
Based on inetic!olecular "heory #$ntermolecular %orces
LEARNING OUTCOMES…
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5.2.1 The properties of Liquids5.2.1 The
properties of Liquids1. Volume and Shape
has a defnite volumedefnite volume but not a defnite shape.not a defnite shape.
√ the particles are arranged closely but notrigidly.
√ held together by a strong intermolecular orcesbut not strong enough to hold the particlesfrmly in place.
√ ∴ particles able to move reely. thus, a liquid ows to ft the shapeliquid ows to ft the shape o its container
and is confned to a certain volume.confned to a certain volume.
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The properties of LiquidsThe
properties of Liquids
gas liquid
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The properties of LiquidsThe
properties of Liquids2.2. CompressibilityCom
pressibility in liquid, the particles are pac ed
closely together. thus, there is very little empty space. ∴ liquids are much more di!cult tomore di!cult to
compresscompress than gas.
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The properties of LiquidsThe
properties of Liquids3.3. Di usionDi usion
di"usion rate o a liquid is much less thanless thangases.gases.
due to #√ molecules are closely pac ed compared to
gases.
√ lower inetic energylower inetic energy than gases.√ stronger intermolecular attractive orcesstronger intermolecular attractive orces
between the molecules compared to gases.
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The properties of LiquidsThe properties of Liquids.. Surfa!e tensionSurfa!e tension
is the amount o energyamount o energy required to stretchto stretchthe sur acethe sur ace o a liquid by a unit area.by a unit area.
√
Liquid molecules e$periencedintermolecular attractive orces in allalldirectionsdirections by their neighbouring molecules.
√
however, molecules at the sur acemolecules at the sur ace arepulled downward and sidewaysdownward and sideways rom theneighbouring molecules.
√but not upwardbut not upward away rom the sur ace.
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S"#$%C& T&'S()'S"#$%C& T&'S()'
Particles at thesurface
Particles withinthe liquid
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√ these intermolecular attractive orceswill pull the molecules into the liquid.pull the molecules into the liquid.
√ cause the sur ace to stretch andtighten.
√ the stronger the intermolecularstronger the intermolecular
attractiveattractive orces, the higher the sur acehigher the sur acetension.tension.
S"#$%C& T&'S()'S"#$%C& T&'S()'
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The properties of LiquidsThe properties of Liquids5. Vis!osity
is resistance o liquid to ow. the greater a liquid%s viscosity , the more
slowly it ows. viscosity decreases as temperature
increases.
&$ample o substance that have highviscosity # molten lava and honey.
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Vis!osityVis!osity
depends on #√ the si'e o the molecules#the si'e o the molecules#
the higher the molar masshigher the molar mass , the moremore
resistance their owresistance their ow , ∴ more viscous theliquid.
√ the strengthstrength o intermolecular attractiveattractive
orcesorces between the molecules# the stronger the attractive orcesstronger the attractive orces , the
higher the viscosity.higher the viscosity.
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5.2.2 Vaporisation *ro!ess5.2.2 V aporisation *ro!ess a process in which molecules escape romescape rom
liquid into gaseousliquid into gaseous state through a sur acethrough a sur ace
( a process in which liquid is trans ormedliquid is trans ormedinto gas.into gas.
√ molecules in a liquid move quite reely.√ each molecule possesses a di"erent
magnitude o inetic energy.√ some molecules have a relatively high
inetic energies.
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Vaporisation *ro!essVaporisation *ro!ess√ when the inetic energy is su!cient enough
to overcome the attractive orces that bindthem, the molecules will loosen themselvesand be evaporated o".
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Vaporisation *ro!essVaporisation *ro!ess vaporisation rate depends on #
√ Surfa!e areaSurfa!e area
) the larger the sur ace area, the
higher the chances or the moleculesto escape rom the sur ace.
) sur ace area increases, evaporationsur ace area increases, eva poration
rate increases.rate increases.
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Vaporisation *ro!essVaporisation *ro!ess√ TemperatureTem perature
) as temperature is increasedtem perature is increased , thetotal number o molecules with high
inetic energy is increased.) ∴ more molecules have enoughenergy to escape rom the sur ace o
the liquid.) thus evaporation rate increases.eva poration rate increases.
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Vaporisation *ro!essVaporisation *ro!ess
√ (ntermole!ular attra!tion for!es(ntermole!ular attra!tion for!es
) the wea erthe wea er the intermolecular
attraction orcesattraction orces , the asteraster theevaporation rate.
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molecules escape rom the sur ace o aliquid # re erred as vapour molecules.vapour molecules. in an open system #
√ vapour molecules which evaporate o"will di"use away.
in a closed system #
√ vapour molecules which leaves thesur ace cannot escapecannot escape rom the system.
Vaporisation *ro!essVaporisation *ro!ess
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*apourisation +in a closed container√
they remain in the container.√ in contact with the surface of the liquid.√ these vapour molecules are in constant random
motion.√ continually strike with:
the wall of the container.
other vapour molecules.the surface of the liquid
molecules.
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√ everytime the vapour molecules hitthe wall o the container, pressure ise$erted.
√pressure e$erted by the vapourmolecules above the sur ace o theliquid is called the *- /01 1& 01&.
Vaporisation *ro!ess
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Vaporisation pro!essVaporisation pro!ess
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Vapourisation pro!essVapourisation pro!ess√ however, some o the vapour molecules maysome o the vapour molecules may
loselose their inetic energyinetic energy during the collision.√ they do not have enough energy to remain as
vapour molecules.
√ they reached the sur ace o the liquid.√ trapped by the attractive orces.√ i they cannot overcome the attractive orces,
these vapour molecules return as liquidmolecules.
√ the process is nown as 3/4 &4 -67/43/4 &4 -67/4 ..
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6he change ostate o a liquid intoliquid intoa vapoura vapour occuring atatthe sur acethe sur ace o aliquid at anyat anytemperatures andtemperatures and
pressures.pressures.
6he change o state o aliquid into a vapourliquid into a vapour occuring on the innerinnersur ace o the liquidsur ace o the liquid at acertain temperaturecertain temperature owhich the vapour pressure
is equal to the atmosphericequal to the atmosphericpressure.pressure.
6he temperature is called
the boiling point.boiling point.
V%*)#(S%T()' +)(L(',
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the temperature at which the vapourpressure of liquid is equal to the externalatmospheric pressure.
+oilin- *oint+oilin - *oint
the temperature at which the vapourpressure of liquid is equal to the standardatmospheric pressure (1 atm).
'ormal +oilin- *oint'ormal +oilin - *oint