Download DG o rxn

‫?‪What is Thermodynamics‬‬
‫• به مجموعه روشهای ریاضی که به ما کمک می کنند تا‬
‫بتوانیم وضعیت یک واکنش را از نظر انجام پذیر بودن‬
‫در شرایط خاص ( دما و فشار معین) بررسی نماییم و‬
‫بتوانیم وضعیت تعادل را پیش بینی کنیم ترمودینامیک‬
‫گویند‪ .‬ترمودینامیک در ارتباط با زمان رسیدن به‬
‫شرایط خاص یا تعادل (سینتیک) اطالعاتی در اختیاری‬
‫ما نمی گذارد‪.‬‬
Thermodynamic Systems Definitions
Isolated System: No matter
or energy cross system
boundaries. No work can be
done on the system.
Open System: Free exchange
across system boundaries.
Closed System: Energy can be
exchanged but matter cannot.
Adiabatic System: Special
case where no heat can be
exchanged but work can be
done on the system (e.g. PV
work).
Thermodynamic State Properties
• Extensive: These variables or properties
depend on the amount of material present
(e.g. mass or volume).
• Intensive: These variables or properties
DO NOT depend on the amount of
material (e.g. density, pressure, and
temperature).
Idealized Thermodynamic Processes
• Irreversible: Initial system state is unstable or
metastable and spontaneous change in the
system yields a system with a lower-energy final
state.
• Reversible: Both initial and final states are
stable equilibrium states and the path between
them is a continuous sequence of equilibrium
states. NOT ACTUALLY REALIZED IN
NATURE.
Spontaneous Reaction Direction
Product-Favored Reactions
In general, product-favored
reactions are exothermic.
E.g. thermite reaction
Fe2O3(s) + 2 Al(s)  2 Fe(s) +
Al2O3(s)
DH = - 848 kJ
‫‪First Law of Thermodynamics‬‬
‫قانون اول ترمودینامیک همان قانون بقای انرژی است‬
‫هر سیستمی دارای انرژی درونی است (‪)E‬‬
‫انرژی درونی هر سیستم منزوی مقداری است ثابت که قابل‬
‫محاسبه نیست اما تغییرات آن قابل اندازه گیری است‪.‬‬
‫‪DE=Ef-Ei‬‬
‫‪Ef-Ei=q-w‬‬
‫•‬
‫•‬
‫•‬
‫•‬
‫‪ q‬مثبت ‪ :‬گرما جذب شده توسط سیستم‬
‫‪ q‬منفی ‪ :‬گرما دفع شده توسط سیستم‬
‫‪ w‬منفی ‪ :‬کار انجام شده توسط سیستم‬
‫‪ w‬مثبت ‪ :‬کار انجام شده روی سیستم‬
‫‪qA≠qB‬‬
‫‪wA≠wB‬‬
‫‪DEA=DEB‬‬
‫‪qA-wA=qB -wB‬‬
‫روش محاسبه تغییرات انرژی درونی در‬
‫شرایط مختلف‬
w= PV
1- Constant Volume : (P2-P1)V=DPV=>w=0
DE=qv
2- Constant pressure : P(V2-V1)=PDV
DE=qp- PDV ; qp=DE+ PDV ; qp=DH
H=E+PV
‫درشرایطی که یک واکنش شیمیایی ذاتا با‬
‫تغییر حجم همراه باشد‬
N2O4(g)  2NO2(g)
PVA=nART ; PVB=nBRT
PDV= PVA-PVB =nART-nBRT=RTDn
DH=DE+RTDn
‫‪Second Law of Thermodynamics‬‬
‫قانون دوم ترمودینامیک ‪ :‬هر تغییر خود به خودی با‬
‫افزایش بی نظمی همراه است‪.‬‬
‫ون‬
‫س َماء بَنَ ْینَا َها ِبأ َ ْی ٍد َو ِإنَّا لَ ُمو ِسعُ َ‬
‫َوال َّ‬
‫وما آسمانها را با قدرت بناکردیم و همواره آن را‬
‫وسعت می بخشیم‬
‫آیه ‪ 47‬ذاریات‬
Entropy and Phase
Vapour
So (J/K•mol)
H2O(gas)
Ice
188.8
H2O(liq)
69.9
H2O (s)
47.9
Water
S (gases) > S (liquids) > S (solids)
Entropy and Temperature
The entropy of a substance increases with
temperature.
Higher T means :
• more randomness
• larger S
Entropy and complexity
Increase in molecular complexity
generally leads to increase in S.
So (J/K•mol)
CH4
248.2
C 2H 6
336.1
C 3H 8
419.4
Entropy of Ionic Substances
• Ionic Solids : Entropy depends on extent
of motion of ions. This depends on the
strength of coulombic attraction.
ion pairs
So (J/K•mol)
MgO
Mg2+ / O2-
26.9
NaF
Na+ / F-
51.5
• Entropy increases when a pure liquid
or solid dissolves in a solvent.
Standard Entropies, So
• Every substance at a given temperature and in a
specific phase has a well-defined Entropy
• At 298o the entropy of a substance is called
So
- with UNITS of J.K-1.mol-1
• The larger the value of So, the greater the degree of
disorder or randomness
e.g. So (in J.K-1mol-1) : Br2 (liq) = 152.2
Br2 (gas) = 245.5
For any process:
DSo =  So(final) -  So(initial)
DSo(vap., Br2) = (245.5-152.2) = 93.3 J.K-1mol-1
Calculating DS for a Reaction
DSo
=  So (products) -  So (reactants)
Consider 2 H2(g) + O2(g)  2 H2O(liq)
DSo = 2 So (H2O) - [2 So (H2) + So (O2)]
DSo = 2 mol (69.9 J/K•mol) [2 mol (130.7 J/K•mol) + 1 mol (205.3 J/K•mol)]
DSo = -326.9 J/K
Note that there is a decrease in S because 3 mol of
gas give 2 mol of liquid.
If S DECREASES,
why is this a SPONTANEOUS REACTION??
2nd Law of Thermodynamics
A reaction is spontaneous (product-favored) if
DS for the universe is positive.
DSuniverse = DSsystem + DSsurroundings
DSuniverse > 0 for product-favored process
First calc. entropy created by matter dispersal (DSsystem)
Next, calc. entropy created by energy dispersal (DSsurround)
Calculating DS(universe)
2 H2(g) + O2(g)  2 H2O(liq)
DSosystem = -326.9 J/K
DS o surroundings =
q surroundings
T
- DH o system
=
T
Can calculate that DHorxn = DHosystem = -571.7 kJ
- (-571.7 kJ)(1000 J/kJ)
298.15 K
DSosurroundings = +1917 J/K
DS o surroundings =
Calculating DS(universe) (2)
2 H2(g) + O2(g)  2 H2O(liq)
DSosystem
= -326.9 J/K (less matter dispersal)
DSosurroundings
= +1917 J/K (more energy dispersal)
DSouniverse
= +1590 J/K
The entropy of the universe increases
so the reaction is spontaneous.
The Laws of Thermodynamics
1. Two bodies in thermal equilibrium are at same T
Energy can never be created or destroyed.
DE =q-w
2. The total entropy of the UNIVERSE
( = system plus surroundings) MUST INCREASE
in every spontaneous process.
D STOTAL = D Ssystem + D Ssurroundings > 0
Gibbs Free Energy, G
DSuniv = DSsurr + DSsys
DSuniv =
DHsys
T
+ DSsys
Multiply through by -T
-TDSuniv = DHsys - TDSsys
-TDSuniv = change in Gibbs free energy
for the system = DGsystem
Under standard conditions —
DGo
=
DHo
-
TDSo
The Gibbs
Equation
Standard Gibbs Free Energies, DGof
• Every substance in a specific state has a
Gibbs Free Energy, G = H - TS
• recall: only DH can be measured. Therefore:
there is no absolute scale for G
• only DG values can be determined
• DGof the Gibbs Free Energy of formation (from
elements) is used as the “standard value”
• We set the scale of G to be consistent with that for H -
DGof for elements in standard states = 0
Sign of Gibbs Free Energy, DG
DGo = DHo - TDSo
• change in Gibbs free energy =
(total free energy change for system - free energy lost in
disordering the system)
• If reaction is exothermic (DHo is -) and
entropy increases (DSo is +), then
DGo must be - and reaction CAN proceed.
• If reaction is endothermic (DHo is +), and
entropy decreases (DSo is -), then
DGo must be +; reaction CANNOT proceed.
Gibbs Free Energy changes for reactions
DGo = DHo - TDSo
DHo
DSo
exo (-)
endo(+)
exo (-)
endo(+)
increase(+)
decrease(-)
decrease(-)
increase(+)
DGo
Reaction
+
?
?
Product-favored
Reactant-favored
T dependent
T dependent
Spontaneous in last 2 cases only if
Temperature is such that DGo < 0
Methods of calculating DG
DGo = DHo - TDSo
Two methods of calculating DGo
a) Determine DHorxn and DSorxn and use Gibbs equation.
b) Use tabulated values of free energies of formation,
DGfo.
DGorxn =  DGfo (products) -  D Gfo (reactants)
Calculating DGorxn
EXAMPLE: Combustion of acetylene
C2H2(g) + 5/2 O2(g)  2 CO2(g) + H2O(g)
From standard enthalpies of formation: DHorxn = -1238 kJ
From standard molar entropies: DSorxn = - 0.0974 kJ/K
Calculate DGorxn from DGo = DHo - TDSo
DGorxn = -1238 kJ - (298 K)(-0.0974 kJ/K)
= -1209 kJ
Reaction is product-favored in spite of negative
DSorxn. Reaction is “enthalpy driven”
Calculating DGorxn
DGorxn =
 DG o (products) -  DG o (reactants)
f
f
EXAMPLE 3: Combustion of carbon
C(graphite) + O2(g)  CO2(g)
DGorxn = DGfo(CO2) - [DGfo(graph) + DGfo(O2)]
DGorxn = -394.4 kJ - [ 0 + 0]
Note that free energy of formation of an element in
its standard state is 0.
DGorxn = -394.4 kJ
Reaction is product-favored as expected.
Free Energy and Temperature
2 Fe2O3(s) + 3 C(s)  4 Fe(s) + 3 CO2(g)
DHorxn = +467.9 kJ
DSorxn = +560.3 J/K
DGorxn = 467.9 kJ - (298K)(0.560kJ/K) = +300.8 kJ
Reaction is reactant-favored at 298 K
At what T does DGorxn just change from (+) to (-)?
i.e. what is T for DGorxn = 0 = DHorxn - TDSorxn
If DGorxn = 0
then
DHorxn = TDSorxn
so T = DHo/DSo ~ 468kJ/0.56kJ/K = 836 K or 563oC
DGo for COUPLED CHEMICAL REACTIONS
Reduction of iron oxide by CO is an example of using TWO
reactions coupled to each other in order to drive a
thermodynamically forbidden reaction:
Fe2O3(s)  2 Fe(s) + 3/2 O2(g)
DGorxn = +742 kJ
with a thermodynamically allowed reaction:
3/2 C(s) + 3/2 O2 (g)  3/2 CO2(g)
Overall :
Fe2O3(s) + 3/2 C(s)  2 Fe(s) + 3/2 CO2(g)
DGorxn= +301 kJ @ 25oC
BUT
DGorxn = -592 kJ
DGorxn < 0 kJ for T > 563oC
Other examples of coupled reactions:
Coupled reactions VERY COMMON in Biochemistry :
e.g. all bio-synthesis driven by
ATP  ADP for which DHorxn = -20 kJ
DSorxn = +34 J/K
DGorxn = -30 kJ at 37oC
Thermodynamics and Keq
• Keq is related to reaction favorability.
• If DGorxn < 0, reaction is product-favored.
• DGorxn is the change in free energy as reactants
convert completely to products.
• But systems often reach a state of equilibrium in
which reactants have not converted completely
to products.
• How to describe thermodynamically ?
DGrxn versus DGorxn
Under any condition of a reacting system, we can define
DGrxn in terms of the REACTION QUOTIENT, Q
DGrxn = DGorxn + RT ln Q
If DGrxn < 0 then reaction proceeds to right
If DGrxn > 0 then reaction proceeds to left
At equilibrium, DGrxn = 0. Also, Q = K. Thus
DGorxn = - RT lnK
Thermodynamics and Keq (2)
2 NO2  N2O4
DGorxn = -4.8 kJ
• pure NO2 has DGrxn < 0.
• Reaction proceeds until DGrxn
= 0 - the minimum in
G(reaction) - see graph.
• At this point, both N2O4 and
NO2 are present, with more
N2O4.
• This is a product-favored
reaction.
Thermodynamics and Keq (3)
N2O4 2 NO2
DGorxn = +4.8 kJ
• pure N2O4 has DGrxn < 0.
• Reaction proceeds until
DGrxn = 0 - the minimum in
G(reaction) - see graph.
• At this point, both N2O4 and
NO2 are present, with more
NO2.
• This is a reactant-favored
reaction.
Thermodynamics and Keq (4)
Keq is related to reaction favorability and so to
DGorxn.
The larger the value of DGorxn the larger the
value of K.
DGorxn = - RT lnK
where R = 8.31 J/K•mol
Thermodynamics and Keq (5)
DGorxn = - RT lnK
Calculate K for the reaction
N2O4  2 NO2
DGorxn = +4.8 kJ
DGorxn = +4800 J = - (8.31 J/K)(298 K) ln K
4800 J
lnK = = - 1.94
(8.31 J/K)(298K)
K = 0.14
When DGorxn > 0, then K < 1 - reactant favoured
When DGorxn < 0, then K >1 - product favoured
‫رابطه بین دما و ثابت تعادل‬
K2
DH  T2  T1 


log
=
K1 2.303R  T2T1 
o
‫ترمودینامیک سلولی‬
‫تمرینهای پایان فصل‬
‫‪• 4-6-8-10-14-16-18-20-24-28-32-34-36-38‬‬‫‪40-42-44‬‬
ELECTROCHEMISTRY
CHAPTER 20
‫اجزاء ماده‬
‫انواع ماده‬
‫‪ -2-1-1‬جريان‬
‫‪ -3-1-1‬پتانسيل‬
‫‪ -4-1-1‬مقاومت‬
‫‪ -5-1-1‬مدار الکتريکي‬
Recall
Oxidation – LOSS of electrons
Reduction – GAIN of electrons
Oxidation number –
For a monatomic ion the oxidation no. = the
actual charge of the atom
or it is the hypothetical charge assigned to the
atom using a set of rules.
Make sure YOU know how to assign oxidation
numbers!!!!
Oxidation occurs at the ANODE
Reduction occurs at the CATHODE
Oxidising agent/oxidant – The substance that
causes oxidation of another substance and
hence it is reduced.
Reducing agent/reductant – The substance that
cause reduction of another substance and
hence it is oxidised.
ELECTRIC CURRENT = transfer of charge
METALLIC CONDUCTION = flow of electrons
with no movement of the atoms of the metal
ELECTROLYTIC (IONIC) CONDUCTION =
electric current by movement of ions through a
solution or pure liquid
Cu2+(aq)
Ag+(aq)
Oxidizing and reducing agents in direct contact.
Cu(s) + 2 Ag+(aq)  Cu2+(aq) + 2 Ag(s)
Zn strip inserted into
CuSO4 solution
Zn(s)  Zn2+(aq) + 2eCu2+(aq) + 2e-  Cu(s)
ANODE Cu/ Cu2+(1.00M) // Ag+ (1.00M)/ Ag CATHODE
ANODE Zn / Zn2+ (1.00M) // Cu2+ (1.00M) / Cu CATHODE
ANODE Pt/ Fe2+(0.10M), Fe3+(0.20M)// Ag+(1.00M)/ Ag CATHODE
Cell EMF
1J
1V =
1C
• Electromotive (“causing electron motion”) force (emf) is
the force required to push electrons through the external
circuit.
• Cell potential: Ecell is the emf of a cell. Also referred to
as cell voltage and positive for spontaneous cell
reactions.
Cell EMF
• Emf depends on specific reactions that occur at the
cathode and anode, the concentration of reactants
and products and the temperature.
• For 1M solutions at 25 C (standard conditions), the
standard emf (standard cell potential) is called
Ecell.
• Standard conditions include 1M concentrations for
reactants and products in solution and 1 atm
pressure for those that are gases. e.g. for Zn-Cu
voltaic cell,
Zn(s) + Cu2+(aq, 1M)
Zn2+(aq, 1M) + Cu(s) Eocell= +1.10V
Cell EMF
• Cell potential is difference between two electrode
potentials; one associated with the cathode and the
other with the anode.
• The potential associated with each electrode is
chosen to be the potential for reduction to occur at
that electrode.
• The cell potential Eocell, is given by the standard
reduction potential of the cathode reaction minus
that of the anode reaction.
Eocell = Eored(cathode) - Eored(anode)
• Standard reduction potentials, Ered are measured
relative to the standard hydrogen electrode (SHE).
0.76
H2 in
Anode
Zn+2
SO4-2
1 M ZnSO4
Cathode
H+
Cl1 M HCl
Spontaneity of Redox
Reactions
• In a voltaic (galvanic) cell (spontaneous) Ered(cathode) is
more positive than Ered(anode) since
E cell = E red cathode   E red anode 
• A positive E indicates a spontaneous process (galvanic
cell).
• A negative E indicates a nonspontaneous process.
Spontaneity of Redox
Reactions
EMF and Free-Energy Change
• We can show that
DG = nFE
• DG is the change in free-energy, n is the number of moles
of electrons transferred, F is Faraday’s constant, and E is
the emf of the cell.
• We define
1F = 96,500 Cmol = 96,500 J/V·mol
• Since n and F are positive, if DG > 0 then E < 0.
Effect of concentration
DG = DG  RT ln Q
o
Since DGo = -nFEo and DG = -nFE
RT
Nernst equation
E=E 
ln Q
nF
2.303RT
o
E=E 
log Q
nF
0.05916
o
E=E 
log Q at 25oC
n
o
0.05916
E=E 
log Q
n
o
Use the Nernst equation to:
- find the EMF produced by a cell under nonstandard conditions.
- determine the concentration of reactant or
product by measuring the EMF of the cell.
Example:
Consider the reaction:
Zn(s) + Cu2+(aq)  Zn2+ (aq) + Cu(s)
Calculate the cell emf when:
[Cu2+] = 5.0 M and [Zn2+] = 0.5 M
Since emf depends on concentration, a voltaic cell with
a non-zero emf can exist using the same species in both
the anode and cathode compartments.
CONCENTRATION CELL
Anode:
Cathode:
Ni(s)  Ni2+(aq) + 2eNi2+(aq) + 2e-  Ni(s)
Eored = -0.28V
Eored = -0.28V
Eocell = Eored(cathode) - Eored(anode)
= (-0.28 V) – (-0.28 V) = 0V
But the cell is operating under non-standard conditions
since concentrations are  1 M.
Driving force of cell due to the difference in
concentration  tries to equalise
concentrations in both compartments.
Anode:
Cathode:
Ni(s)  Ni2+(aq, dil) + 2eNi2+(aq, conc) + 2e-  Ni(s)
Ni2+(aq, conc)  Ni2+(aq, dil)
2
[
Ni
]dil
0
.
05916
o
E=E 
log 2
n
[Ni ]conc
0.05916
(1.00  103 )
E = (0V) 
log
2
(1.00)
E = 0.0887 V
NOTE:
When the concentrations in the 2 compartments
become equal,
Q = 1 and E = 0 V.
EMF and Equilibrium
Why does the emf drop as a voltaic cell
discharges?
0.05916
log Q
Look at Nernst equation: E = E 
n
o
As reactants are converted to products, Q
increases.
Eventually E = 0 V.
Since DG = -nFE, DG = 0 kJ/mol
 equilibrium!
i.e. when E = 0 V,  equilibrium
 no net reaction
The equilibrium constant can be calculated for
a redox reaction as follows:
At equilibrium:
E = 0 V and Q = K
0.05916
E=E 
log Q
n
o
0.05916
0=E 
log K
n
o
nEo
 log K =
0.05916
‫ قابل جمع نیست‬E
3
0.771 V
2
0.440 V
Fe  
 Fe  
 Fe
‫؟‬
-440/0+771/0=331/0
DGFe3 / Fe2  DGFe2 / Fe = DGFe3 / Fe
 nFEFe3 / Fe2  nFEFe2 / Fe = nFEFe3 / Fe
EFe3 / Fe = -0.036
‫نمودار زیر را تکمیل نموده و‬
‫در صورتی که گاز ‪ NO‬در محلول اسیدی با ‪ pH‬یک دمیده شود چه گونه هایی از نیتروژن‬
‫در محلول ایجاد می گردند‬
‫بیشترین کار مفید‬
‫‪i=0‬‬
Study of redox
reactions
Batteries
Fuel cells
Manufacturing
of chemicals
‫كاربردهاي الكتروشیمي‬
Electroplating
and refining
of metals
Bioelectrochemistry:
study of electron
transfer in biological
regulations of
organisms
Study and
control for
corrosion
‫انواع سیستمهاي الكتروشیمیایي‬
‫گالواني ‪DG<0‬‬
‫باتری‪ ،‬پیل سوختی‪ ،‬زنگ زدن فلزات(خوردگی فلزات) ‪،‬‬
‫محافظت کاتدی‬
‫الكترولیتي ‪DG>0‬‬
‫تجزیه الکتریکی مواد (الکترولیز)‪ ،‬آبکاری فلزات‪ ،‬تولید مواد‬
‫شیمیایی‬
‫قطب ‪+‬‬
‫قطب ‪-‬‬
‫واكنش كاتد‬
‫واكنش آند‬
‫پیل الكترولیتي‬
‫آند‬
‫كاتد‬
‫احیا‬
‫اكسیداسیون‬
‫پیل گالواني‬
‫كاتد‬
‫آند‬
‫احیا‬
‫اكسیداسیون‬
‫الکترولیز آب‬
‫تاريخچه كشف باتري‬
‫تاريخچه توليد باتري به زمان حکومت اشکانيان يعني‬
‫حدود سه قرن پيش از ميالد حضرت مسيح (ع) باز‬
‫‪.‬گرددمي‬
‫اين باتري که توسط محققين اطريش ي در سال ‪1993‬‬
‫در اطراف بغداد در محلي به نام خواجه ربو پيدا شد‬
‫هم اکنون با نام باتري بغداد در جهان شناسايي مي‬
‫شود‪.‬‬
‫قطب منفي ‪ :‬ميله آهن‬
‫قطب مثبت ‪ :‬استوانه مس‬
‫الکتروليت ‪ :‬آب ميوه هاي ترش مزه‬
‫ولتاژ‪ 5/1-2 :‬ولت‬
Primary batteries
Modern ZincManganese
battery
Leclanché’s
battery
(1866)
Georges Leclanché
(1839-1882)
Anode: Zn  Zn2+ + 2eCathode: 2MnO2 + 2H2O +2e-  2MnOOH + 2OH-
Seal
Zn-container
MnO2 paste
(cathode)
Carbon rod
NH4OH
electrolyte
Gas space
Electrolyte:
Zn2+
2NH4Cl
+2OH-
 Zn(NH3)Cl2 + 2H2O
Zn-container
2MnO2 + Zn + 2NH4Cl  2MnOOH + Zn(NH3)Cl2
MnO2 paste
(cathode)
Carbon rod
Gel electrolyte
Grove’s fuel cell (1839)
O2
Sir William Grove
1811–1896
4H+ + 4e- 2H2
2H2O - 4e- O2 + 4H+
H2
Fuel Cells performance improving
Raising the voltage:
Raising the current:
Connection
of cells
Cell
stackin series
• Increasing the temperature
• Increasing the area of
eelectrode electrolyte interface
• The use of catalyst
Cathode catalyst
Anode catalyst
Bipolar
electrode
H2
O2
Stack of several hundred
Electrolyte frame
Bipolar plate
ANODE
ELECTROLYTE
CATHODE
ANODE
ELECTROLYTE
ANODE
CATHODE
ELECTROLYTE
ANODE
CATHODE
ELECTROLYTE
CATHODE
ANODE
ANODE
ELECTROLYTE
ELECTROLYTE
CATHODE
CATHODE
ANODE
ELECTROLYTE
CATHODE
‫استخراج فلزات‬
Electrolysis of NaCl solution
2H2O = 2H+ +2e – + ½ O2 E=1.23
2 Cl– = Cl2 + 2e– E=1.35
Battery
e
oxidation
A
N
O
D
E
2Na+ + 2e– = 2Na E= -2.74
O2 +4e – + 2H2O = 4OH- E= -0.41
e
C
A
T
H
O
D
E
reduction
Salt solution consists of Na+ and Cl– ions
‫تولید مواد‬
Production of aluminum
Aluminum (Al), the third most abundant elements on Earth crust as bauxite or alumina Al2O3,
remain unknown to man until 1827, because it is very reactive. By then, Wohler obtained some
Al metal by reducing Al2O3 with potassium vapore.
In 1886, two young men electrolyzed molten cryolite Na3AlF6 (melting point 1000° C), but did
not get aluminum.
Hall and Heroult tried to mix about 5% alumina in their molten cryolite, and
obtained Al metal. This is the Hall process.
AlF63– + 3 e–  Al + 6 F– . . . Cathode
2 Al2OF62– + C(s) + 12 F–  4 AlF63– + CO2 + 4 e– . . . Anode
2 Al2O3 + 3 C  4 Al + 3 CO2 . . . Overall cell reaction
Charge required for each mole Al = 3 F
Energy required = 3 F DE
Electrolysis of acid solution
H2O = ½ O2 + 2e– + 2 H+ Battery
e
oxidation
A
N
O
D
E
e
2H+ + 2e– = H2
C
A
T
H
O
D
E
reduction
Solutions containing H+ and SO42– ions
Charges required to produce 1 mole H2 and ½ moles O2 = 2F
Energy required = 2 F DE
Electrolysis of H2SO4 solution
Pure water is not a good electric conductor. In the presence of
electrolytes, water can be decomposed by electrolysis.
On the other hand, electrolysis of electrolyte solutions may reduce H+
and oxidize O2– in H2O.
In an H2SO4 solution,
cathode reductions are
2 H2O (l) + 2 e– = H2 (g) + 2 OH–
(same as 2H+ + 2e– = H2)
Anode oxidation:
2 H2O (l) = 4 e– + O2 (g) + 4 H+
2 SO42– = [SO3O–OSO3]2– + 2 e–
E o = -1.23 V (observed)
E o = 2.01 V (not observed)
Electrolysis of H2SO4 solution
E o = 1.23 V
E o = 2.01 V
2 H2O (l) = 4 e– + O2 (g) + 4 H+
2 SO42– = [SO3O–OSO3]2– + 2 e–
Battery
e
oxidation
A
N
O
D
E
e
2H+ + 2e = H2
reduction
C
A
T
H
O
D
E
Solution consists of H+ and SO42– ions
Corrosion:
Unwanted Voltaic Cells
Fe(s)  Fe2+ (aq) + 2e–
O2 + H2O (l) + 4e–  4 OH– (aq)
2 Fe(s) + O2 + H2O
 2 Fe2+ (aq) + 4 OH– (aq)
What are effective corrosion
prevention methods?
Coating
Use sacrifice electrode
Cathodic protection of an underground
pipe.
‫تمرینهاي پایان فصل‬
‫‪ 2‬و ‪ 4‬و ‪6‬و ‪24‬و ‪26‬و ‪28‬و ‪30‬و‪ 32‬و ‪34‬و‬
‫‪36‬و ‪38‬و ‪40‬و ‪42‬و ‪44‬و ‪46‬و ‪48‬و ‪50‬و‬
‫‪52‬و ‪54‬و ‪56‬و ‪58‬و ‪60‬و ‪62‬و ‪64‬و ‪66‬و‬
‫‪68‬و ‪72‬و ‪74‬و ‪.75‬‬
The Transition Elements
and Coordination
Compounds
‫‪Complex Ions and‬‬
‫‪Coordination Compounds‬‬
‫• شیمیدانان اواخر سده نوزدهم میالدی‬
‫برای درک ماهیت پیوند در ترکیبات‬
‫مولکولی یا برکیبات مرتبه باالتر با‬
‫دشواری روبرو بودند‪ .‬تشکیل ترکیبی‬
‫با فرمول ‪ CoCl3.6NH3‬گمراه کننده‬
‫بود به ویژه در مواردی مثل مورد‬
‫فوق که ترکیب ‪ CoCl3‬به تنهایی‬
‫وجود ندارد‪.‬‬
‫در سال ‪ 1893‬آلفرد ورنر نظریه ای برای توضیح این گونه‬
‫ترکیبات را ارائه داد‪.‬‬
Complex Ions and
Coordination Compounds
A pair of electrons on the oxygen atom of H2O forms
a coordinate covalent bond to Fe2+.
Complex Ions and
Coordination Compounds
• Transition-metal atoms often function as
Lewis acids, reacting with groups called
ligands by forming coordinate covalent
bonds to them.
The metal atom with its ligands is a complex
ion or neutral complex.
Basic Definitions
A complex ion is a metal ion with Lewis bases
attached to it through coordinate covalent
bonds.
A complex (or coordination compound) is a
compound consisting either of complex ions and
other ions of opposite charge (for example, the
compound K4[Fe(CN)6] of the complex ion
Fe(CN)64- and four K+ ions)
Basic Definitions
Ligands are the Lewis bases attached to the
metal atom in a complex.
They are electron-pair donors, so ligands may be
neutral molecules (such as H2O or NH3) or anions
(such as CN- or Cl-) that have at least one atom
with a lone pair of electrons.
The coordination number of a metal atom in a
complex is the total number of bonds the metal
atom forms with ligands (2-12).
Basic Definitions
In [Fe(H2O)6]2+, the iron atom bonds to each
oxygen atom in the six water molecules,
therefore, the coordination number of the
iron ion is 6.
6 is the most common coordination number
although compounds of coordination
number 4 are also well known.
Polydentate Ligands
• A bidentate ligand (“two-toothed” ligand)
is a ligand that bonds to a metal atom
through two atoms of the ligand.
Ethylenediamine is an example.
Polydentate Ligands
• In forming a complex, the ethylenediamine
molecule bends around so that both
nitrogen atoms coordinate to the metal
atom, M.
Polydentate Ligands
• The oxalate ion, C2O42-, is another
common bidentate ligand.
Polydentate Ligands
• A polydentate ligand (“having many
teeth”) is a ligand that can bond with two
or more atoms to a metal atom.
A complex formed by polydentate ligands is
frequently quite stable and is called a chelate
(pronounced "key-late").
Chelating ligands bonded to metal – rings – chelate rings
any number of atoms in the ring
most common – five or six atoms, including metal
"The adjective chelate, derived from the great claw
or chela (chely - Greek) of the lobster, is suggested
for the groups which function as two units and
fasten to the central atom so as to produce
heterocyclic rings."
Porphyrin
Naming Coordination
Compounds
• The IUPAC has agreed on a nomenclature
of complexes that gives basic structural
information about the species.
The following rules outline this nomenclature
system.
Naming Coordination
Compounds
• The name of the cation precedes the
name of the anion.
For example,
K4[Fe(CN)6] is named
potassium hexacyanoferrate(II)
cation
anion
Naming Coordination
Compounds
• The name of the cation precedes the
name of the anion.
For example,
[Co(NH3)6]Cl3 is named
hexaamminecobalt(III) chloride
cation
anion
Naming Coordination
Compounds
• The name of the complex consists of two
parts written as one word. Ligands are
named first followed by the metal atom.
For example,
[Fe(CN)6]4- is named
hexacyanoferrate(II) ion
ligand
name
metal
name
Naming Coordination
Compounds
• The name of the complex consists of two
parts written as one word. Ligands are
named first followed by the metal atom.
For example,
[Co(NH3)6]3+ is named
hexaamminecobalt(III) ion
ligand
name
metal
name
Naming Coordination
Compounds
• Ligands are listed alphabetically using
Greek prefixes such as di, tri, tetra, etc.,
for multiples of a given ligand.
Anionic ligands end in –o.
Bromide, BrCarbonate, CO32Cyanide, CNOxalate, C2O42Sulfate, SO42Oxide, O2-
bromo
carbonato
cyano
oxalato
sulfato
oxo
Naming Coordination
Compounds
• Ligands are listed alphabetically using
Greek prefixes such as di, tri, tetra, etc.,
for multiples of a given ligand.
Neutral ligands are given the name of the
molecule with the following exceptions.
Ammonia, NH3
Carbon monoxide, CO
Water, H2O
ammine
carbonyl
aqua
Naming Coordination
Compounds
• When the name of a ligand also has a
number prefix, the number of ligands is
denoted with bis (2), tris (3), tetrakis (4),
and so forth.
For example,
[Co(en)3]Cl3 is named
tris(ethylenediamine)cobalt(III) chloride
3
ligand
name
Naming Coordination
Compounds
• If the complex is an anion, the metal
name must end in –ate followed by its
oxidation state in parentheses.
When there is a Latin name for the metal, it is
used to name the anion.
Copper
Gold
Iron
Lead
Silver
Tin
Cuprate
Aurate
Ferrate
Plumbate
Argenate
Stannate
Oxidation States
• Most of the transition elements have a
doubly filled s subshell making a +2
oxidation state relatively common.
In addition, d electrons can be lost, producing
many polyvalent transition metal ions.
Isomerism
•
Structure and Isomerism in
Coordination Compounds
• Coordination
compounds provide
many special types of
constitutional
isomers (ionization
isomers).
Here are two cobalt isomers.
[Co(NH3)5(SO4)]Br
a red compound
[Co(NH3)5Br]SO4
a violet compound
Hydrate Isomers
• Geometric isomers are isomers in which
the atoms are joined to one another in the
same way, but occupy different relative
positions in space.
Optical isomers, or enantiomers, are isomers
that are nonsuperimposable mirror images of
one another.
Cis-trans isomers of
Co(NH3)4(NO2)2+
Nonsuperimposable Mirror
Images.
Nonsuperimposable Mirror
Images.
Isomers of CoCI2(en)2+
Covalent bond formation between atoms X and Y.
2+
• Fe
: [Ar], 4s,
6
3d ,

3p
3d
4s
4p
Crystal Field Theory (CFT)
Fe 2+ : [Ar], 3d6,4s
1s+3p+2dsp3d2
Octahedral Geometry.
The colour can change depending
on a number of factors e.g.
1. Metal charge
2. Ligand
Figure 23.5: Chromate-dichromate equilibrium.
Return to slide 13
Figure 23.28: The electronic transition responsible for the visible absorption in
Ti(H2O)63+.
Return to slide 47
Physical phenomenon
‫تمرینهاي پایان فصل‬
‫‪ 2‬و ‪ 4‬و ‪6‬و ‪13‬و ‪14‬و ‪16‬و ‪18‬و‬
‫‪20‬و ‪22‬و ‪.28‬‬
Figure 23.4: Aqueous chromium ion.
Return to slide 12
Figure 23.27: Color and visible spectrum of Ti(H2O)63+. Photo courtesy of James Scherer.
Return to slide 47
Return to slide 51
Return to slide 2
Figure 23.1: Classification of the transition elements.
Return to slide 4
Return to slide 6
Return to slide 9
Return to slide 9
Return to slide 3
CHAPTER 27
NUCLEAR
CHEMISTRY
The Nucleus
• Two types of submicroscopic particles
reside in the nucleus
– protons: +1 charge
– neutrons: 0 charge
• Protons and neutrons are referred to as
nucleons
• The nucleus of any given element will
contain an identical number of protons
• Nuclei of any given element can contain
different numbers of neutrons
• The “normal” chemistry of an element is
determined by the number of protons (the
atomic number, Z) in the nucleus (which
equals the electrons surrounding the
nucleus)
• Nuclear chemistry is dependent on both
protons and neutrons
• Isotopes are nuclei of any given element
which contain different numbers of neutrons
• The mass number, A, is the total number
of nucleons in the nucleus
The Nucleus
(cont.)
• Many isotopes are stable, I.e., they do not
undergo radioactive decay
– all isotopes of any element with Z>83 are
radioactive
• Nuclear notation conventions:
mass number
(total # of nucleons)
atomic number
(# of protons)
e.g.,
39
19
K
A
Z
X
symbol of the
element
Potassium-39; nucleus
contains 19 protons
and 20 neutrons
Radioactivity
• Nuclide is a general term used for
referring to isotopes of either the same or
different elements
• A radioactive isotope is called a
radionuclide
Nuclear Decay
The nuclei of radioactive isotopes are in an “excited”,
unstable state. They move toward stability by
“decaying” through emitting various particles,
electromagnetic radiation, or capturing orbiting
electrons (quantum mechanics tells us there is a
finite probability of orbital electrons residing in the
nucleus for very brief intervals). Nuclear decay
processes continue until, finally, a stable isotope is
formed
Predicting Radioactivity
• The most stable nuclear configuration is a
nucleus in which both the protons and neutrons
are present in “magic” numbers (2, 8, 20, 50,
82,114,126, or 184).
• The next most stable nuclear structure is when
there is an even number of both protons and
neutrons (even-even nuclei).
• The least stable nuclear configuration is where
there is an odd number of both neutrons and
protons (odd-odd nuclei).
21_475
202
80
120
Unstable region
(too many neutrons;
spontaneous beta
production)
100
Number of neutrons (A–Z)
Hg (1.53:1 ratio)
80
60
110
48
Cd
(1.29:1 ratio)
40
Unstable region
(too many protons;
spontaneous positron
production)
20
6
3
0
0
20
Li (1:1 ratio)
40
60
80
Number of protons (Z)
100
• Odd-even or even-odd (proton-neutron) nuclei
are intermediate in stability.
• These “rules” are more applicable to “heavy”
nuclei (A>20) than to “light” nuclei (e.g., 6Li, 10B
and 14N, which are odd-odd nuclei, are all
stable; 18F and 22Na are radioactive).
• As nuclei get “heavier”, more neutrons, relative
to the number of protons, are required to
achieve stability.
Radioactive Emissions
• Alpha () radiation
– alpha particles are identical with the doubly
charged helium ion: 24 He2+, i.e., the nucleus of
helium
– the charge is ordinarily omitted
• Beta () radiation
– beta particles are identical with electrons: -1e
(emitted at high energy)
– in beta decay, a neutron in a nucleus is
converted to a proton
• Gamma ( ) radiation
–  rays are high energy (high frequency, short
wave-length) electromagnetic radiation: 0
– gamma rays accompany many (most) nuclear
transformations, but do not alter either the
atomic number or the mass number; they allow
the nucleus to “deexite” from higher energy
levels to lower energy levels by carrying away
the excess energy
Radioactive Emissions (cont.)
• Positron (+) emission
– a positron is equivalent to a positively charged
electron: +10e
– in positron emission, a proton in the nucleus is
effectively transformed into a neutron
0
40
19K
40
18Ar
+
+1e
Radioactive Emissions (cont.)
– positrons have extremely short life times in
nature, as they interact immediately with
electrons; the positron/electron pair is
“annihilated”, and 1.022 million electron volts
(MeV) of energy is emitted as two 0.511 MeV
gamma rays at 180° to one another
Summary of Nuclear Emissions
Balancing Nuclear Equations
• In balancing nuclear equations, the total number of
nucleons must be equal on both sides of the equation
• When a nucleus emits an  particle, Z decreases by
two, and A decreases by four in the daughter nucleus
• When a nucleus emits a  particle, Z increases by one
and A remains constant in the daughter nucleus
• When a nucleus emits a  +, or a K electron is
captured, Z decreases by one and A remains constant
in the daughter nucleus
Balancing Nuclear Equations
(cont.)
 Americium-241 decays by
emission:
237
241
95Am
93Np
 Uranium-237 decays by  emission:
237
92U
237
93Np
+
0
-1e
4
+ 2He
Balancing Nuclear Equations
(cont.)
 Carbon-11 decays by + emission
11
6C
11
5B +
0
+1e
Nuclear Transmutation
• Nuclear transmutation is the conversion of one
element, or isotope, to another using nuclear
reactions
– nuclear reactors are used as a source of neutrons
for the most common type of nuclear
transmutation
– particle accelerators are used to bombard a target
nucleus with charged particles (usually +), such
as protons, alpha particles, carbon-12 nuclei, etc.
Nuclear Transmutation
(cont.)
• The first nuclear transmutation was observed by Ernest
Rutherford, who bombarded nitrogen-14 nuclei with
alpha particles from radium to produce oxygen-17
14
7N
•
4
+ 2He
1
1H
17
+ 8O
In the shorthand used by nuclear chemists, this
reaction would be written:
14
7
N (,p)
17
8O
Nuclear Transmutation
(cont.)
• None of the elements with atomic numbers
>92 exist in nature (on the earth). Their
half-lives are too short. They have been
produced using nuclear transmutation . Two
other elements, technicium and
promethium, are produced as fission
products in nuclear reactors, or by
bombarding molybdenum and neodymium,
respectively, with neutrons.
Nuclear Reaction Problems
Problem 10.1 Radium-233 is a radioactive
-emitter. Write the nuclear equation for
this emission event, and identify the
product.
Problem 10.2 Radium-230 is a radioactive
-emitter. Write the nuclear equation for
the event, and identify the product.
Problem 10.3 Sodium-21 is a radioactive
positron emitter. Write the nuclear equation
for the event, and identify the product.
Radioactive Decay
• Radioactive decay is the loss of radioactivity
when a radioactive element emits nuclear
radiation
• The decay of radioisotopes found in nature
results in the formation of products called
daughter nuclei, which may or may not be
radioactive
• A series of nuclear reactions that begins with an
unstable nucleus and ends with the formation of
a stable one is called a nuclear decay series or
nuclear disintegration series
Half-Life
Amount of Radioisotope
Remaining
If the amount of radioisotope at time
zero is defined as No, and the amount remaining
after n half-lives is N, then the fraction of isotope
remaining after n half-lives is
N
No
=
1
2
( )
n
Half-Life
The half-life is the amount of time
during which the radioisotope decays
by 50%
Half-life Problems
Problem 10.4 Estimate how much of a
radioisotope will be left after six half-lives.
Problem 10.5 Calculate the percentage of
radioisotope remaining after 5.0 half-lives.
Problem 10.6 Calculate the percentage of
radioisotope remaining after 3.8 half-lives.
Nuclear Dating Methods
• Carbon-14 dating
14
6C
14
7N
0
+ -1e
• Used to date materials which incorporate
carbon, e.g., paper, cloth, bones, leather,
etc.
– t½ for carbon-14 is 5730 years
– the older the sample, the less accurate is
carbon-14 dating
– assumes that the carbon-12/carbon-14 ratio in
nature has stayed about the same
Biomedical Applications
Effects of Radiation
Penetrating Power
of Radiation Types



paper
aluminum
lead
Chemical Effects of Radiation
High energy radiation produces not only
ions along its penetration track, but free
radicals as well.
primary radiation event
H2O + radiation
H2O+ + e- (aq)
secondary chemical processes
H2O+ + H2O
H3O.+ + .OH
e- (aq) + H2O
.H
+ OH-
single unpaired electron characteristic
of a free radical is shown as a dot on
the appropriate atom
Chemical Effects of Radiation
(cont.)
Free radicals may abstract a hydrogen
atom from a donor biomolecule, which
then produces a biomolecule free
radical.
.R-NH
.OH + H-R-NH
HOH
+
2
2
Biomolecule free radical may now
combine with itself or another
biomolecule. If that biomolecule is an
enzyme or a nucleic acid, normal
function may be severely altered and
cellular activity adversely affected.
Protection from Radiation
Minimize exposure to high-energy
radiation: 1) use a radiation-absorbing
barrier, 2) maximize the distance of
separation, and 3) limit the time of
exposure
inverse-square law
I≈
1
d2
The intensity of the radiation I is
proportional to the reciprocal of the
square of the distance d from the
origin of the radiation
Problem
Problem 10.7 If the distance between a
source and target is 6 m, how far should
the source be moved to decrease the
radiation intensity ot one-fourth of its
current value?
Detection of Radiation
• Radiation is detectable because the particles (including
 rays) interact with atoms and molecules to form ions
• Photographic film was the first way radiation was
observed (by exposing the film), and is still used in film
badges
• Geiger counters are metal tubes with thin “windows”
which contain an ionizable gas at low pressure.
Interaction with ionizing radiation causes a pulse of
electricity
Detection of Radiation
(cont.)
• Scintillation counters use a crystal (typically NaI) in
which the discharge of the ions formed by radiation
results in a small flash of light, which is converted to an
electrical pulse using a photomultiplier tube. This
detection method does not work for  particles or low
energy ’’s.
• The most common detection technology used now (for
’s) is a single crystal of ultra-pure Ge
• For  and  particles, Si detectors are used
Radiation Units
• Curie (Ci)
– 1 Ci = 3.7 X 1010 nuclear disintegrations per second
(the disintegration rate of 1g of pure Ra)
• Becquerel (Bq)
– the SI unit for radioactivity. It is equal to 1
disintegration per second
• Röntgen (R)
– the Röntgen is the oldest radiation unit; it is
applicable only to  and X-rays
– 1R = 1.61 X 1015 ion-pairs created/kg of air, or an
absorbed energy of
8.8 X 10-3 J kg-1
Radiation Units
(cont.)
• rad (radiation absorbed dose)
– 1 rad = the absorption of 0.01 J kg-1
– 1 R = 0.88 rad
• Gray (Gy):
– The SI unit for absorbed dose. It is equal to 1 J kg-1.
Therefore, 1 Gy is equal to 100 rads
• rem (Rntgen equivalent for man)
– Takes into acccount the relative biological
effectiveness (RBE) for different kinds of radiation
– RBE=1 rads
for x, β,
and γ =rays
and 10 for α-paritcles,
x RBE
rems
protons, and neutrons
Effects of Short-Term Exposure
Clinical Uses
• Diagnostic use requires that the radiation
have significant penetrating power to be
accurately detected; that is, it should be
primarily a γ-emitter
• Therapeutic use requires intentional
damage to abnormal (cancerous) tissue;
therefore the isotope should be an α- or βemitter
Biomedical Applications
Radiation Sources
Biological Effects of Radiation
• Somatic effects are the effects of radiation
on the person exposed
• Genetic effects are those which cause
changes in the genome and can be passed
on to future generations
Radiation and Medicine
 Radioisotopes in medicine:
 diagnostic: 43Tc; 6C
Positron
Emission
Tomography
(PET)
Tomograms
Normal
Brain
Alzheimer’s
Brain
Radiation and Medicine
(cont.)
 Therapeutic
• physiological targeting: the use of a
radioisotope which is bound
physiologically to the target organ for
radiation therapy
• iodine-131, which goes essentially
entirely into the thyroid is used to
attack thyroid tumors
• “manual” targeting: the implantation of
an encapsulated radioactive source,
e.g., radium-226, or iridium-192, into
a tumor
Nuclear Fission
• Fission is the splitting of a nucleus into two
smaller “fragment” nuclei
– the most common fission reaction is the bombardment
of uranium-235 with neutrons
235
92U
1
+ 0n
236
*
[ 92U ]
36Kr
92
141
+ 56Ba + 3 0n
1
• Different fission products may be produced when
the uranium-236 nucleus breaks apart (fissions);
the rule that the total number of nucleons must be
present on both sides of the reaction is obeyed
Nuclear Fission
(cont.)
• Since only one neutron is required to produce a fission
in uranium-235, and slightly more than 2.5 neutrons are
produced (on average) in fission, it is possible, under
the right conditions, to have self-sustained fission
reactions occur
– a certain mass of fissionable material is required to
have a self-sustained reaction, referred to as the
critical mass
– in an atomic bomb, a subcritical mass is made to
become supercritical very rapidly, resulting in an
explosion
Nuclear Fission
(cont.)
– in nuclear reactors, the power is regulated by
inserting, or withdrawing, rods, called control
rods, which contain a material (usually
cadmium) which has a very high tendency to
capture neutrons
Nuclear Reactor
Heat Transfer in Nuclear
Reactor
Nuclear Fusion
• Fusion is the combination of lighter nuclei to
form a heavier nucleus
– hydrogen to helium: 4 1H 2He
+ 2 4+1e
1
0
– fusion is the principal energy source for stars
(and our sun)
– the energy from fusion is a result of the fact that
the mass of the helium nucleus is less than the
mass of the four hydrogen nuclei that are
“fused”; the energy output may be calculated
using the Einstein Equation: E = mc2
– extracting fusion energy for power is
complicated by the very high temperatures
required and containment