13th 14th thermodynamics

8/9/2019 13th 14th Thermodynamics

1/55

hemical Thermodynamics

Part II: Fundamentals and

Spontaneity

Louie Paolo D. CarpioInstructor 3

Institute of Chemistry, UP Diliman


2/55

OBJECTIVES for today

1. Discuss the different laws of

thermodynamics

2. Define entropy3. Define Gibbs free energy

. Define spontaneity in terms of

thermodynamic parameters


3/55

SI!!S that you "ill need

1. !ol"ing for G# ! #$ and wor% of

processes.

2. Determine whether a chemicalreaction is spontaneous or not.


4/55

&hermodynamics

&'$()*D+,-)C!/ the study of

the energy transfers accompanyingphysical and chemical changes


5/55

Laws of &hermodynamics

1. 0eroth law / thermal euilibrium

2. 1stLaw energy

3. 2ndLaw / entropy

. 3rd

Law / perfect crystal


6/55

1stLaw of &hermodynamics

Law of Conser"ation of $nergy/energy in the uni"erse is constant

$system 4 $surroundings


7/55

1stLaw of &hermodynamics

n any process# the total change inthe energy of a system 4$5 is eualto the sum of the transferred heat

between the heat and thesurroundings

$system 6 w

w wor%

7wor% / all types of energy e8cept heat

heat


8/55


9/55

9or% and heat at constant pressure

w Pe8ternal4:5

r8n nL(4';r8n5

#: < ;# wor% is done by the

system since w = ;#: = ;# wor% is done on thesystem since w < ;

# $nthalpy of reaction


10/55


11/55


12/55

Con"entions

Energy of thesystem

decreased

Energy of thesystem

increased

Change inenergy of the

system (Esys)

Heat is

released

Heat is

absorbedHeat (q)

Work is done

by the system

Work is done

on the systemWork (w)

(-)(+)

Thermodynamic

variable


13/55

Difference between

' and

$

BombCalorimeter

Coffee-cupcalorimeter

Instrument

used to

quantify

Heat at

constantvolume, w =

Heat at

constant

pressure

Heat

EHCriteria


14/55

(elation between

' and

$

' $ 6 4P:5

#' and $ are e8pressed in >oules

# P is in Pascal 41;132? Pa 1 atm5

# : is in m34;.;;1 m3 1 liter5

#4P:5 45 wor%

@rom $ 6 wA


15/55

Con"ersion of con"entional

chemistry units into >oules

7( B.31 mol1E1

4gas constant in terms of >oules5

f P is in atm and : is in liters#their product can be con"ertedinto >oules by multiplying the ratio

of the gas constant (.

( )( ) >oules

EmolatmL;.;B21

Emol

CB.31

:P litersatm =


16/55

P: for reactions in"ol"ing solids

and liuids only

&a%e note that the product ofpressure and "olume for solidsand liuids can be ignored since

their molar "olume is typically ;.1F of that for a gas.

P: "ery small

4for solids and liuids5


17/55

P: for reactions in"ol"ing gases

4P:5 4ngas5(&

@rom the ideal gas euation

ngas

4ngaseous products

5 / 4ngaseous reactants

5

where


18/55

(elation between

' and

$ for

chemical reactions w gases

' $ 6 4P:5

' $ 6 4ngas5(&

since 4P:5 4ngas5(&


19/55

!pontaneous Processes

definition / a spontaneous processis one that mo"es the reaction

system to euilibrium

# Hsually proceeds with a decreasein energy

# Proceed from more ordered to

more random states 4greater

entropy5


20/55

$,&(*P+

denoted by the symbol !

# )easure of disorder

# Change in entropy is a state

function

! !final/ !initial

# HnitA E


21/55

$,&(*P+

@or re"ersible processesA

&

1I!

processre"ersible=

7 re"ersible processes cause

infinitesimally small changes in

thermodynamic states P# :# & or n.$8ampleA adding 1;; of heat but the

temperature almost did not increase


22/55

$,&(*P+

n general#

2. !gas< !liuid< !solids

3. ncreasing the temperature of a

substance increases its entropy

7 $ntropy is hard to uantify. 'ow do

we compute the entropies ofsubstancesJ


23/55


24/55

3rdLaw of &hermodynamics

- completely ordered purecrystalline solid has an entropy of

Kero at ; E 4absolute Kero5.

# 3rd law of thermodynamics is the

basis of the numerical scale of

entropy


25/55

3rdLaw of &hermodynamics

!ince ! is a state function and

assume that the initial state of a

substance is a perfect crystalline

solid at ; EA

! !final/ !perfect crystalline solid

! !final/ !initial

! !final/ ;

! !o standard molar entropy


26/55

!tandard )olar $ntropies

# $ntropy of a substance at 1 atm

and a gi"en temperature 4usually

2?oC5

# Denoted by the !o

# Hnits of >oule per mole per Eel"in

4molE5


27/55

!tandard )olar $ntropies

# n general# as molecules becomemore comple8 in structure# there

are more ways for atoms to mo"e

about with respect to one another#leading to a higher entropy.

$8. molecular o8ygen "s oKone

;

3*;

2* !!

>reactants>i

iproductsir8n !n!nI!

# $ntropy is also a state function.


30/55

$8ample

!ol"e for the ! of the reactionbelowA

!o"aluesA

'2*24l5 1;.M Emol

'2*4l5 M.1 Emol

*24g5 2;?.; Emol

2 '2*24l5N 2 '2*4l56 *24g5


31/55

$,&(*P+ and !pontaneity

# &he entropy change of the uni"erse4system and surroundings5

determines the spontaneity of a

chemical reaction.

# n spontaneous changes# the

uni"erse tends toward a state

of greater disorder.


32/55

2ndLaw of &hermodynamics

# - net increase in the entropy of theuni"erse results to a spontaneous

reaction

!uni"erse !system6 !surroundings

!uni"erse< ; 4spontaneous5


33/55


34/55

Change in entropy of a chemical r8n

# $ntropy of a chemical reaction

increases ifA

. the molar "olume of the products is

greater than that of the reactants

?. the temperature of a reaction system

increased

M. &he reaction produces gases or thesolid is diminished. @ormation of

gases are fa"ored since !gas< !liuids >reactants

o

f#>i iproducts

o

f#i

o

r8n

GnGnG

# !tandard free energy change at 1 atmand 2?oC.

# Gfo is the standard energy of

formation or free energy contentQ ofsubstances similar to 'f

o.

$ l


41/55

$8ample

!ol"e for the Go

of the reactionbelowA

Gfo"aluesA

'2*24l5 12;. %mol

'2*4l5 22B.M %mol

*24g5 ; %mol

2 '2*24l5N 2 '2*4l56 *24g5

Gibb ' l h lt $ ti


42/55

Gibbs'elmholtK $uation

# Pro"ides the relationship between G# ' and ! at a gi"en temperature

in EA

Gr8n 'r8n &!r8n

f the reaction is in standard

conditions

Go

'o/ &

!o

Gibb @ d t it


43/55

Gibbs @ree energy and spontaneity

@or a spontaneous reaction# G = ;

G

' &

!

- chemical reaction would always bespontaneous ifA

2. 'reaction= ;

3. !reaction< ;

Gibb @ d t it


44/55

Gibbs @ree energy and spontaneity

n general# spontaneous chemical

reactions in"ol"eA

Roth ' and ! must be considered to be

able to predict the spontaneity of a reaction.

!ome endothermic reactions arespontaneous. !ome reactions in"ol"ing a

decrease in entropy can be spontaneous. G

must be computed to accurately predict the

spontaneity of a chemical reaction.

1. (elease of heat or e8othermic 4' = ;5

2. ncrease in entropy 4! < ;5

$ l


45/55

$8ample

!ol"e for the Goof the reaction belowA

2 CB'1B4l56 2? *24g5N 1B '2*4l56 1M C*24g5

!"#"$- %&'#&(H2O(l)

%$(#)*- ("(#'$O2(!)

%'#$*O2(!)

('&- %*"#""H#"(l)

$o(%&'mol)Hfo (%&mol)$ubstance

$ l


46/55

$8ample

!ol"e for the

!

o

of the reaction belowA

*@24g56 '2*4g5N *24g56 2 '@4g5

'o 323.2 %mol

Go 3?B. %mol

$8press your answer in Emol.

Ch i Gibb @ $ G


47/55

Change in Gibbs @ree $nergy#

G

(ecallA 4system is a chemical reaction5

( ) = > >reactants>i iproductsir8n GnGnG

G < ;# nonspontaneous

G = ;# spontaneous

G ;# euilibrium

Gibb @ d ilib i


48/55

Gibbs @ree energy and euilibrium

@or a reaction in euilibrium# G ;

G

' / &

! ;

- chemical reaction is in euilibriumif the reaction is re"ersible and both

re"ersible reactions occur at the

same rate.

(eactants Products

$ ilib i ti


49/55

$uilibrium reactions

@or a reaction in euilibrium# G ;

&he rate of formation of products iseual to the rate of degradation of

reactants at euilibrium.

(eactants Products

Phase changes at their phase changetemperatures are euilibrium

reactions.

Ph h d ilib i


50/55

Phase changes and euilibrium

'2*4l5 '2*4s5at ;oC

Phase changes at their phase change

temperatures are euilibrium reactions.

GfreeKing Gmelting ; 4at ;oC5

'ence# at ;oC# melting and freeKing

occurs at the same rate. 4

G ;5

Gibbs 'elmholt S e ilibri m


51/55

Gibbs'elmholtK S euilibrium

G ' / &! ;

' / &

! ;

' &!

!

'

&

=

Gibbs 'elmholtK S euilibrium


52/55

Gibbs'elmholtK S euilibrium

!ignificance of euationA

2. &his is the minimum temperature at

which a reaction would be

spontaneous if !r8n< ;.

3. &his & is the estimated phase

change temperature in Eel"in for a

phase change reaction.

reaction

reaction

!

'& =

$8ample


53/55

$8ample

$stimate the boiling point of C'3

*'

gi"en the following thermodynamic

data belowA

C'3*'4l5N C'3*'4g5

%("#&$ +.mol- %#!! k+molCH(/H0g1

$%!#& +.mol- %(&! k+molCH(/H0l1

2oHfosubstance

$8ample


54/55

$8ample

$stimate at which temperature in Eel"in

will the reaction below will becomespontaneousA

CaCl24s5N Ca4s56 Cl24g5

$*#! +.mol- )"'#& k+molCaCl%0s1

%%(#) +.mol k+molCl%0g1

*$#*% +.mol k+molCa0s1

2oHfosubstance

$,D *@ CL-!!


55/55

$,D *@ CL-!!

# Chapter co"eredA Chapter 1?

# ,e8t meetingA Problem !et dayO

# ,e8t topicA $lectronic !tructure of-toms

#TH$!&*,!JJJJ

13th 14th thermodynamics

Documents