phychem introduction

7/25/2019 PhyChem Introduction

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What is Physical Chemistry?

The term "physical chemistry" was coined by Mikhail Lomonosoin!#2$ when he presented a lect%re co%rse entitled "& Co%rse in Tr%ePhysical Chemistry" '(%ssian) *+,-. .011 4567.8 9:; niersity@ABDn the preamble to

these lect%res he >ies deEnition) "Physical chemistry is the sciencethat m%st eFplain %nder proisions o= physical eFperiments thereason =or what is happenin> in compleF bodies thro%>h chemicaloperations"
https://en.wikipedia.org/wiki/Mikhail_Lomonosovhttps://en.wikipedia.org/wiki/Petersburg_Universityhttps://en.wikipedia.org/wiki/Physical_chemistryhttps://en.wikipedia.org/wiki/Physical_chemistryhttps://en.wikipedia.org/wiki/Petersburg_Universityhttps://en.wikipedia.org/wiki/Mikhail_Lomonosov


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DGT(HICTDHG TH PJKDC&L CJMDT(K

PHYSICAL CHEMISTRY

the branch o= science that is concernedwith the physical principles that %nderli

chemistry seeks to acco%nt =or the str%ct%re o=

matter and the chan>es it %nder>oes interms o= =%ndamental concepts s%ch asatoms$ electrons$ and ener>y@

proides the basic =ramework =or allother branchesN inor>anic$ or>anic$

biochemistry$ en>ineerin>


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proides the basis o= modern methods o= nalysis$ thedetermination o= str%ct%re$ and the el%cidation o= themanner by which chemical reaction occ%r@

it establishes the link between the properties o= b%lk matterand the behaior o= particlesN atoms$ ions$ or molec%lesNo=which it is composed@

Dn >eneral sense$ !hysical chemistryis deEned as the st%dy

o= macroscopic$ atomic$ s%batomic$ and partic%latephenomena in chemical systems in terms o= laws andconcepts o= physics@ Dt applies the principles$ practices andconcepts o= physicss%chas motion$ ener>y$ =orce$ time$ thermodynamics$ O%ant%m

chemistry$ statistical mechanics and dynamics$ eO%ilibri%m@
https://en.wikipedia.org/wiki/Physicshttps://en.wikipedia.org/wiki/Physicshttps://en.wikipedia.org/wiki/Physicshttps://en.wikipedia.org/wiki/Physics


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tates o= Matter and the properties o= ases

the broadest classiEcation o= b%lk matter is into one o= the

three physical statesN solid$ liO%id$ and >as the three states o= matter can be reco>niQed by their behaior

when they are enclosed in a container)

solidN retains its shape independent o= the shape o= thecontainer it contains

liO%idN a R%id state o= matter that possesses a wellNdeEneds%r=ace and 'in a >raitational Eelds< Ells the lower part o= thecontainer it occ%pies

>asN a R%id state o= matter that Ells the container it occ%pies


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The essential diSerence

between the three stateso= matter comes down tothe =reedom o= particles

to moe past the other@


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D= the particles are widely separated on aera>e$ there ishardly any restriction on their motion$ and the s%bstance isa >as@

D= the particles interact so stron>ly with each other that theyare locked to>ether$ then the s%bstance is a solid@

D= the particles hae an intermediate mobility betweenthese eFtremes$ the nthe s%bstance is a liO%id@


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Dn this chapter$ well see how to describe >ases$ the simplesto= these three states o= matter@&ltho%>h >ases are simpleNboth to describe and in terms o= their internal str%ct%reNthey are o= immense importance@


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The description o= tates

o= Matter the term state has many diSerent meanin>s in

chemistry

e@>@ the states o= matter N solid state$ liO%id

state$ >aseo%s state by state we shall mean a partic%lar condition o=

a sample o= matter that is described in terms o=the ol%me$ press%re temperat%re and amo%nto= s%bstance present@


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Uol%me

the ol%me o= a sample is a meas%re o= the

space it occ%pies

Press%re$ p$ we mean =orce ddiided by the

area on which =orce is eFerted@N press%re is meas%red in the %nit called pascal$

Pa)

!" #$A


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Press%re nits and Conersion Vactors

SI% !ascal & Pa' 1 Pa" 1 ( m )*

bar ! bar !X # Pa

atmosphere ! atm !X!@32# kPa

torr YX torr ! atm

! Torr !33@32 Pa


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Temperat%re

Temperat%re$ T$ o= an obZect is a property thatdetermines in which direction ener>y will Rowwhen it is in contact with another obZect

ener>y 'heat< Rows =rom the hi>hertemperat%re to the lower temperat%re@

when the two bodies hae the sametmeprat%re$ there is no net Row o= heatbetween them@ These bodies are in thermal

e,uili+rium


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[elin scaleN more conenient to %se in many scientiEc applications@

Temperat%re Conersion)

Celsius

A\C 'A\V ] 32< ^ #_B

-el.in

A[ #_B'A\V ` YXram 'k>

c%rrently deEned as the mass o= a certain blocko= platin%mNiridi%m alloy presered at eres$o%tside Paris@

Dn Chemistry$ where the =oc%s is on thebehaior o= atoms$ it is %s%ally more %se=%l toknow the n%mber o= atoms$ molec%les$ or ions

in a sample rather than the mass o= a sample


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! mole o= particle is eO%al to the n%mber o= atoms in eFactly !2 > o=CarbonN!2@

Dn practice$ 1 mole= 6.02214 x 10 23particles

&o>adro constant$ N& 6.02214 x 10 23

n n%mber o= particles/n%mber o= particles per

mole

G/G&

F@ ) @ F !X 22 C% atoms corresponds to X@!# mol !@ mol e contains how many e atoms?


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molar mass$ M$ is the massper mole o= s%bstance

F@ the molar mass o= C atoms is !2@X! > molN!

the molar mass of an elementmeans the mass per mole o=its atoms@

the molar mass of a com!ouundis the molar mass o= itsmolec%les$ or in the case o= ionic compo%nds$ the mass permole o= its =orm%la %nits@


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a =orm%la %nit is the physical entity correspondin> to a speciEcchemical =orm%la

F@ the =orm%la %nit =or Ga2Hconsists o= two Ga `ions and oneH 2Nion

n " mass of sam!le$molar mass

" m$M

E0 Vind the amo%nt o= atoms present in #@Y >o= @

(ote% the =ormer names =or molar mass were

atomic 2eight$ =or the mass per mole o=atoms$ and molecular 2eight$ =or the massper molec%les$ both terms are still =ar =romdead@


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O%ations o= tate

The state o= any sample o= s%bstance can bespeciEed by >iin> the al%es o= the =ollowin>properties)

U$ the ol%me the sample occ%pies

p$ its press%re

T$ its temperat%re

n$ the amo%nt o= s%bstance it cointains


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the =o%r O%antities are not independent o= one another

i= we select the amo%nt$ the ol%me $ and the temeprat%re$ $we hae to accept a partic%lar press%re

the s%bstance obeys an eO%ation o= state$ an eO%ation thatrelates one o= the =o%r properties

the >eneral =orm o= an eO%ation o= state is

!" f&T3 43 n'


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The Per=ect as O%ation o=tate

oyles and his s%ccessors eFperiments led to the=orm%lation o= the =ollowin> !erfect gase,uation of state%

!4 " nRT

where ($ known as the >as constant$ is a constantwith the same al%e =or all >ases@

R" 56178 /Pa L -)1mol )1


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the per=ect >as eO%ation o= stateN the per=ect >as lawN is soNcalled beca%se it is an idealiQation o= the eO%ations o= statethat >ases act%ally obey@

it is =o%nd that all >ases obey the eO%ation more closely as thepress%re is red%ced toward Qero

the eO%ation is an eFample o= a limiting la2$ a law that is notobeyed eFactly by an act%al >as$ b%t becomes increasin>lyalid as the press%re is red%ced and is obeyed eFactly in thelimit o= Qero press%re@


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Perfect 9as

N a hypothetical R%id that obeys the eO%ation 'the per=ect >as

eO%ation o= state< at any press%re

Real 9as

Nan act%al >as$ which behaes more and more like a per=ect>as as its press%re is red%ced$ and behaes eFactly like a

per=ect >as when the press%re has been red%ced to Qero@


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The per=ect >as law s%mmariQes three sets o= obserations )

oyles LawN at constant temperat%re the press%re o= a EFed

amo%nt o= >as is inersely proprotional to its ol%me@ Whennand t are constant$ the per=ect >as law becomes

pU constant

hence$

p !/U


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Charles Law)

the ol%me o= a EFed amo%nt o= >as atconstant press%re is proportional to the

temperat%re$ T@when n and p areboth constant

U T

N Charles Law indicates that there eFists anabsol%te Qero o= temperat%re$ atemperat%re below which it is impossible tocool an obZect


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&o>adros Principle)

N &t a >ien temperat%re and press%re$ eO%al ol%mes o= >ascontain the same n%mber o= molec%les@

N i= a sample o= air at !XX kPa occ%pies !@XX L at 3XX [$ and asample o= p%re carbon dioFide occ%pies the same ol%me

%nder the same conditions$ then we can in=er that both thesamples contain the same n%mber o= molec%les

N the molar ol%me$ 4m$ o= any s%bstance 'not Z%st a >as< isthe ol%me it occ%pies per mole o= molec%les present in thesample@

N &o>adros principle implies that the molar ol%me o= a >assho%ld be the same =or all >ases at the same temperat%reand press%re@


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sin> the Per=ect as Law )

The per=ect >as law is %sed when we want topredict the press%re o= a >as >ien itstemperat%re$ its chemical amo%nt$ and the

ol%me it occ%pies@

p n(T/U


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Predictin> the press%re o= asample o= >as

!@ What press%re is eFerted by @# > o= oFy>en >asin a Rask o= ol%me 3XX mL at 2X XC ?

2@ Calc%late the press%re eFerted by !@22 > o=carbon dioFide conEned to a Rask o= ol%meYX mL at 3B XC


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Dn case$ that a press%re is >ien %nder one set o=conditions $ and we are asked to predict thepress%re o= the same sample %nder a diSerent

set o= conditions$ we can %se the com+inedgas e,uation

!141$ T1" !*4*$ T*


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F@

What is the Enal ol%me o= a sample o= >as thathas been heated =rom 2# X C to !XXX X C and

its press%re increased =rom !X@X kPa to !#X@XkPa$ >ien that its initial ol%me was !# mL?


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The per=et >as law can also be %sed tocalc%late the molar ol%me o= per=ect >asat any temperat%re and press%re@

Um U/n

'n(T/p


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MiFt%res o= ases) partialpress%res

Ialtons Law)

The press%re eFerted by a miFt%re o= per=ect

>ases is the s%m o= the press%res eFerted bythe indiid%al >ases occ%pyin> the sameol%me alone@"

! total" !A: !;: !C@@

where

N Ialtons law is strictly alid only =or miFt%res o=per=ect >ases ' or =or real >ases at s%ch lowpress%res that they are behain> per=ectlyien that !XX@X> o= air consists o= #@# > o= G2$ 23@2 > o= H2$ and

!@3> o= &r@

partial press%re

pZ FZp

where) pZN partial press%re o= the species Z

FZ N mole =raction o= species Z

p N total press%re


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Calc%latin> partial press%res

Many enironmental and biophysical ar>%mentsdepend on a knowled>e o= the composition o=the atmosphere$ and in partic%lar on the partialpress%res o= its principal components@ ienthat the composition o= the sample o= mass!XX> o= dry air at sea leel is #@# > nitro>en$23@2 > oFy>en$ and !@3 > ar>on$ what is thepartial press%re o= each component at !XX kPatotal press%re?

phychem introduction

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