ch e 102 final review 2010

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Ch E 102 Final Review

N. T. McManus

Fall 2010



Ch E 102 Final Review

� Don¶t f orget Gas Law basics and Stoichiometry

basics

� Read the cover sheet inf o r ight away (given on the

website).� Check the equations given.

� Plan your own help sheet (one page double sided).

� Need help contact me. ± nmcmanus@uwater loo.ca

± DWE 2530A.



Properties of Solutions

� Colligative proper ties: where m istotal molality

� C is molar concentr ation

Electrochemistry� Ner nst equation:

�Reaction Equilibr ia� For a reaction of the type aA +

bB cC + dD the reaction quotientQ is

� Van¶t Hoff equation:�� Arr henius equation

Vapour pr essur e� Clausius-Clapeyron equation:

±±

°

±±

¯

®

!

!

!

!

oi

Poi

Pi

xi

Pdrop pressurevapour

cRT pressureosmotic

m b

K b

Televation point boiling

mf

K f

T depression pointfreezing

Q F n

RT

Qn

ln

K 298Tatlog0592.0

0

0

(!(

!(!(

I I

I I

? A ? A? A ? Aba

d c

BA

DCQ !

¹¹ º

¸©©ª

¨!¹¹

º

¸©©ª

¨

211

2 11ln

T T R

H

K

K (

¹ º

¸©ª

¨!

RT

E Ak

a

oexp

¹¹ º

¸©©ª

¨

(!¹¹

º

¸©©ª

¨

21

0

1

0

2 11ln

T T R

H

P

P vap

T

T



Section 3

Properties of Liquids

� Vapour Liquid Equilibr ium.

� Phase Diagr ams.

� Colligative Properties

� Vapour Pr essur e Depr ession.

± From Raoult¶s law. ± vapour pressure of a solid/liquid solution is lower than that f or

pure solvent.

± Pos = (1-xB) PoA



Section 3

Colligative properties of solutions

� Vapour Pr essur e Depr ession. ± From Raoult¶s law. ± vapour pressure of a solid/liquid solution is lower than that f or

pure solvent. ± Po

s = (1-xB) PoA

� Boiling point elevation ± ¨ Tb = iKb(molality of solute)

� Fr eezing point depr ession ± ¨Tf = -iKf (molality of solute)

� Osmotic pr essur e ± T = h Vg = icRT

� Remember R has to have corr ect units to match with pr essur eunits. (0.082 for atm, 8.314 for Pa and volumes in m3)

± TV = inRT ± The van t¶ Hoff factor ³i´ relates to the degree that ionic solutes

dissociate when they are dissolved.



Section 4

Chemical Equilibr ium

� Know basic concepts

± Equilibr ium often chosen f or wor d questions

� A system will stay at the equilibr ium concentr ations of reactant and products

± This is tr ue unless it is acted upon by some change to the system.

� Chemical equilibr ium is rever sible.

± It does not depend on the way it is approached.

r ate of r eactants to products = r ate of products to

r eactants

? A ? A? A ? A ba

dc

c

BA

DCK !Equilibr ium constant



Section 4


� Kc (Kp) is constant (for a given

temper atur e).

� has units of (concentr ation)(d+c)-(a+b).

� Kc is an intr insic proper ty of the chemical

reaction.

� Mechanistic (sequential reactions) f ollow cer tain

r ules in or der to obtain an over all K




For sequential r eactions

� When two reactions or more are in sequence (mechanistic reaction) ± leading to a single over all balanced reaction equation.

± The individual equilibr ium constants are multiplied to obtain

the K f or the over all reaction.

A B (1)

B C (2)

? A? A A

Bc !

1

? A

? A B

C

c!

2

A C (3)? A? A 213 ccc K K A

C K !!Over all

Reaction



Section 4


� Gas phase reactions

bBa

A

cC

dD

p !

Kc = Kp (RT) (a+b)-(c+d)

�for r eactions involving solids K does not includeany ter m for concentr ation of solid

�For reactions involving solids, only the concentr ationof gas or dissolved reactants is considered explicitly.

Reaction involving solids



Section 4

Chemical Equilibr ium� Pr edicting Dir ection of Change in

Equilibr ium Reactions

� Q is defined f or any concentr ationof reactants and products.

� Q = Kc ± chemical equilibr ium

� Q < Kc ± reactants are in excess.

± System must change to reduce reactants and

increase products� Q > Kc

± products are in excess.

± System must change to reduce products andincrease reactants.

? A ? A? A ? A ba

dc

BA

DCQ !



Section 4


� Le Châtelier Pr inciple: ± ³If a system in equilibr ium is distur bed, it will react in such a way

as to minimize the eff ect of the distur bance

� Increasing concentr ation (or pressure) of a reactant:

± Q < K ± Rate of f or war d reaction > r ate of rever se reaction

± More products are f ormed until Q = K (equilibr ium).

� Increasing the volume (decreasing totalpressure/concentr ation) ± will shift the reaction towar ds the side that has more (gas)

molecules.� Conver sely

� Decreasing volume (increasing totalpressure/concentr ation) ± will shift reaction towar ds side that has least molecules.



Section 4


� Other factor s.

± Catalysts do not change equilibr ium constant

f or a given temper ature

� Just speed up both f or war d and rever se reactions ± Addition of iner t mater ial does not aff ect K.

Make sur e you can execute problems r elating to

changes in chemical equilibr ium



Section 4


± Temper ature is the only factor that changes

the value of K

� All other factor s aff ect Q.

± Exothermic K q as T o. ± Endothermic K o as T q

¹¹ º

¸©©ª

¨!¹¹

º

¸©©ª

¨

211

2 11ln

T T R

H

K

K (

R = 8.314 J/mol K

(H = heat of reaction. In joules



Section 4

Solubility Equilibr ium

� Solubility and Solubility Product

Constant

± For spar ingly soluble electrolytes

Ksp = [Ag+][Cl-]For 1: 1 salt e.g. AgCl

For 1: 2 salt e.g. PbI2Ksp = [Pb2+][I-]2

Ksp = S2

S = [Ag+] = [Cl-]

Ksp = 4S3

S = [Pb2+]

2S = [I-

]



Section 4

Solubility Equilibr ium

� Solubility and Solubility Product

Constant

± For spar ingly soluble electrolytes.

� Common ion eff ect.

± If a soluble f orm of one of the ions is added

then precipitation will occur to a level that

satisfies Ksp.

± Do ICE f or new [M]



Section 5

ELECTROCHEMISTRY

� Oxidation States (OS):

� Balancing electrochemical equations. ± Systematic remember have to balance elements

and charge.� Galvanic (Voltaic) Cells

± Electrons f low from Anode� oxidation.

� Anode: metal is r emoved

± Electrons f low to Cathode� r eduction.

� Cathode: metal is deposited



Section 5

ELECTROCHEMISTRY

� Far aday¶s Law.

F

It

F

Qn !!

n is the moles of electrons

Q is total chargeF is the Far aday constant

t is the time that I is applied f or



Section 5

Elecrochemistry

� Half-cell potentials:

± Cell potentials are assigned to a half-cell only.

± The over all galvanic cell potential may be obtained

when two half-cells are combined. ± Cell potential f or the hydrogen half cell is 0.

� H2 (1atm) p 2H+ + 2e-

� 2H+ + 2e-p H2 (1atm).

� The tendency of the reduction taking place spontaneously (when a given half cell is combined with

a H2 half cell):

± is d efined as a positive potential.



Section 5

Electrochemistry

� Cell Potentials

� E° cell = E° cathode - E° anode.

� Where E° cathode and E° anode are the values obtained f rom the table of reduction potentials.

� i.e don¶t rever se the anode reaction potential in the calculation.

� The half cell with the highest algebr aic E o will occur as the r eduction.

� The magnitude of the cell potential is not aff ected by the size of the cell or the stoichiometr ic coeff icients

needed to balance the reaction.� The stronger the oxidizing agent the higher the

reduction potential.

� Note: gener al r elationships with E o ar e often af avour ite for wor d questions.



Section 5

Electrochemistry

� Ner nst Equation

Qn

RT cell

o

cell ln!

R is the gas constant,

F is the far aday constant

n is the number of moles of electrons tr ansf erred in the balanced cell

r eaction.

Q

n

E E cell o

cell ln02569.0

!

Qn

E E cell o

cell 10log0592.0

!

At

25oC or

�n = actual number of electrons tr ansf err ed in the balanced cell equation.



Section 5

Electrochemistry

� Cell Potentials at Equilibr ium ± Ecell = 0V

� Concentr ation Cells ± When Eo

cell = 0V

± Electrons flows to cell with higher concentr ation

K nF

RT E

cell

o ln!

Qn E cell ln02569.0

!



Section 5

Electrochemistry� Applications� Concentr ation Cells and Solubility Product

± Diff erence in half cell potential in a concentr ation cell based ona spar ingly soluble mater ial can be used to find Ksp

� Electrolysis

± Applied potential must be greater than the cell potential f or the par ticular system.

± In quantitative terms:

± Electrolysis f ollows Far adays law.� ³The number of moles of mater ial oxidized or reduced at an

electrode is related by the stoichiometry of the electrode reaction

to the amount of electr icity supplied´. ± For metals this is propor tional to the charge on the metal ion

pr ior to reduction to metal.

F

It

F

Qn !!

n is the number of moles of electrons supplied to the cell.



Section 6

Chemical Kinetics

? A ? A ? Amn B Ak

d t

Ad

arat e !!

1

� k: r eaction "r ate constant" (normally use small case k)� n : "or der of r eaction" with respect to A.

� m: or der of reaction with respect to B.� n+m: over all or der of r eaction.� Notes.� Impor tant: For a given reaction

± a A + b B p c C� n is not necessar ily equal to a.

� m is not necessar ily equal to b.� m and n must be determined exper imentally.� Or der need not be integer and need not be positive number s.� Units for k� Fir st or der (s-1), Second or der (Lmol-1s-1)



Section 6

Chemical Kinetics

� Method of the Initial Rates

� Use r ate r atios to assess r ate w.r .t

concentr ations of reagents.� Normally a ser ies of reactions given.

� Use data in a logical fashion to cancel

terms and build up knowledge of system.



Section 6

Chemical Kinetics

� Integr ated Rate

Laws

� Fir st Or der

� Second Or der

k t C

C o !ln

oC k t C lnln !

k t C C o

!

11

oC

k t C

11!



Section 6

Chemical Kinetics

� Half lives obtained

f rom integr ated r ate

laws.

� Fir st or der

� Second or der

k t

2ln2/1

!

ok

t 1

2/1 !

Remember for conver sion (X)

o

o

C

C C X

)( !

)1( X C X C C C ooo

!!



Section 6

Chemical Kinetics

� Temper atur e Eff ects

on k

¹ º

¸©ª

¨!

R T

EexpAk a

¹¹ º

¸©©ª

¨!

211

2 11ln

T T R

E

k

k a

A pre-exponential actor

Ea activation energy

T Temper ature in K



Reaction Mechanisms

� Mechanisms ± Elementary Processes ± Molecular ity ± Rate determining step.

� Slowest step in mechanism

± Steady state approximation.� Rate of f ormation of an intermediate = r ate of consumption

of an intermediate

± Reaction mechanism must be consistent with:� Over all reaction stoichiometry� The over all r ate law.

� Use steady state approximation when no defined r ds. ± Find expression f or r ate ± Determine algebr aic f orm f or concentr ation of

intermediate and fit into r ate law



Section 6

Chemical Kinetics

7. Catalysis

� Catalysts increase reaction r ate by

decreasing activation energy.

� Do not change position of equilibr ium

(increases r ates of f or war d and rever se

reactions.

� Form low energy intermediates.� Are not consumed dur ing reaction.

� May be homogeneous or heterogeneous.

ch e 102 final review 2010

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