5.2 liquid state editted lec

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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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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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

5.2 liquid state editted lec

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