what is thermodynamics? به مجموعه روشهای ریاضی که به ما کمک می...

What is Thermodynamics?

ما • به که ریاضی روشهای مجموعه به

یک وضعیت بتوانیم تا کنند می کمک

در بودن پذیر انجام نظر از را واکنش

) معین ) فشار و دما خاص شرایط

وضعیت بتوانیم و نماییم بررسی

ترمودینامیک کنیم بینی پیش را تعادل

زمان. با ارتباط در ترمودینامیک گویند

تعادل یا خاص شرایط به رسیدن

) ما) اختیاری در اطالعاتی سینتیک

. گذارد نمی

Thermodynamic Systems - Definitions

Isolated System: No matteror energy cross systemboundaries. No work can bedone on the system.

Open System: Free exchangeacross system boundaries.

Closed System: Energy can beexchanged 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

E.g. thermite reaction

Fe2O3(s) + 2 Al(s) 2 Fe(s) +

Al2O3(s)

H = - 848 kJ

In general, product-favored reactions are exothermic.

First Law of Thermodynamics

بقای قانون همان ترمودینامیک اول قانوناست است (انرژی درونی انرژی دارای سیستمی )Eهر

است مقداری منزوی سیستم هر درونی انرژیآن تغییرات اما نیست محاسبه قابل که ثابت

. است گیری اندازه قابل

E=Ef-Ei

Ef-Ei=q-w

•q : سیستم توسط شده جذب گرما مثبت•q : سیستم توسط شده دفع گرما منفی•w : سیستم توسط شده انجام کار منفی•w : سیستم روی شده انجام کار مثبت

qA≠qB

wA≠wB

EA=EB

qA-wA=qB -wB

انرژی تغییرات محاسبه روشمختلف شرایط در درونی

w= PV

1- Constant Volume : (P2-P1)V=PV=>w=0

qv

2- Constant pressure : P(V2-V1)=PV

qp- PV ; qp+ PV ; qp

H=E+PV

واکنش یک که درشرایطیهمراه حجم تغییر با ذاتا شیمیایی

باشد

N2O4(g) 2NO2(g)

PVA=nART ; PVB=nBRT

PV PVA-PVB =nART-nBRT=RTn

H=E+RTn

Second Law of Thermodynamics

به : خود تغییر هر ترمودینامیک دوم قانون. است همراه نظمی بی افزایش با خودی

BونCُع EوسCمB َل Gا Eن وBِإ IدJ ْيB Eَأ ب BاهBا Jن Bْي Bن ب مBاء GاَلسBو

بناکردیم قدرت با را آسمانها ومامی وسعت را آن همواره و

بخشیمذاریات 47آیه

S (gases) > S (liquids) > S (solids)

So )J/K•mol(

H2O)gas( 188.8

H2O)liq( 69.9

H2O )s( 47.9Ice Water

Vapour

Entropy and Phase

The entropy of a substance increases with temperature.

Entropy and Temperature

Higher T means :• more randomness• larger S

Entropy and complexity

Increase in molecular complexity generally leads to increase in S.

SSoo )J/K•mol( )J/K•mol(

CHCH44 248.2248.2

CC22HH66 336.1 336.1

CC33HH88 419.4419.4

• Ionic Solids : Entropy depends on extent of motion of ions. This depends on the strength of coulombic attraction.

Entropy of Ionic Substances

• Entropy increases when a pure liquid or solid dissolves in a solvent.

ion pairsion pairs SSoo )J/K•mol( )J/K•mol(

MgOMgO MgMg2+2+ / O / O2-2- 26.926.9

NaFNaF NaNa++ / F / F-- 51.551.5

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: So = So)final( - So)initial(

So)vap., Br2( = )245.5-152.2( = 93.3 J.K-1mol-1

Consider 2 H2(g) + O2(g) 2 H2O(liq)

So = 2 So (H2O) - [2 So (H2) + So (O2)]

So = 2 mol (69.9 J/K•mol) -

[2 mol (130.7 J/K•mol) + 1 mol (205.3 J/K•mol)]

So = -326.9 J/K

Note that there is a decrease in S because 3 mol of gas give 2 mol of liquid.

Calculating S for a Reaction

So = So )products( - So )reactants(

If S DECREASES, why is this a SPONTANEOUS REACTION??

2nd Law of Thermodynamics

Suniverse = Ssystem + Ssurroundings

Suniverse > 0 for product-favored process

First calc. entropy created by matter dispersal (Ssystem)

Next, calc. entropy created by energy dispersal (Ssurround)

A reaction is spontaneous )product-favored( if S for the universe is positive.

Calculating S(universe)2 H2(g) + O2(g) 2 H2O(liq)

Sosystem = -326.9 J/K

T

H- =

T

q =

systemgssurroundingssurroundin

ooS

K 298.15

J/kJ) kJ)(1000 (-571.7 - = gssurroundin

oS

Sosurroundings = +1917 J/K

Can calculate that Horxn = Ho

system = -571.7 kJ

Calculating S(universe) (2) 2 H2(g) + O2(g) 2 H2O(liq)

Sosystem = -326.9 J/K (less matter dispersal)

Sosurroundings = +1917 J/K (more energy dispersal)

The entropy of the universe increases so the reaction is spontaneous.

Souniverse = +1590 J/K

E = q - w

The Laws of Thermodynamics

1. Two bodies in thermal equilibrium are at same T Energy can never be created or destroyed.

2. The total entropy of the UNIVERSE ) = system plus surroundings( MUST INCREASE in every spontaneous process.

STOTAL = Ssystem + Ssurroundings > 0

Gibbs Free Energy, GSuniv = Ssurr + Ssys

Suniv = Hsys

T + Ssys

Go = Ho - TSo

Multiply through by -T-TSuniv = Hsys - TSsys

-TSuniv = change in Gibbs free energy

for the system = Gsystem

Under standard conditions —

The GibbsEquation

Standard Gibbs Free Energies, Gof

• Every substance in a specific state has a Gibbs Free Energy, G = H - TS• recall: only H can be measured. Therefore: there is no absolute scale for G• only G values can be determined

• Gof 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 -

Gof for elements in standard states = 0

Go = Ho - TSo

• change in Gibbs free energy =

(total free energy change for system - free energy lost in disordering the system)

• If reaction is exothermic (Ho is -) and

entropy increases (So is +), then

Go must be - and reaction CAN proceed.

• If reaction is endothermic (Ho is +), and

entropy decreases (So is -), then

Go must be +; reaction CANNOT proceed.

Sign of Gibbs Free Energy, G

Gibbs Free Energy changes for reactions

Ho So Go Reaction

exo )-( increase)+( - Product-favored

endo)+( decrease)-( + Reactant-favored

exo )-( decrease)-( ? T dependent

endo)+( increase)+( ? T dependent

Spontaneous in last 2 cases only ifTemperature is such that Go < 0

Go = Ho - TSo

Methods of calculating G

Two methods of calculating Go

GGoorxnrxn = = GGff

oo )products( - )products( - G Gffoo )reactants( )reactants(

a( Determine Horxn and So

rxn and use Gibbs equation.

b( Use tabulated values of free energies of formation,

Gfo.

Go = Ho - TSo

Calculating Gorxn

EXAMPLE: Combustion of acetylene

C2H2(g) + 5/2 O2(g) 2 CO2(g) + H2O(g)

From standard enthalpies of formation: Horxn = -1238 kJ

From standard molar entropies: Sorxn = - 0.0974 kJ/K

Calculate Gorxnfrom Go = Ho - TSo

Gorxn = -1238 kJ - (298 K)(-0.0974 kJ/K)

= -1209 kJ

Reaction is product-favored in spite of negative Sorxn.

Reaction is “enthalpy driven”

Calculating Gorxn

EXAMPLE 3: Combustion of carbon

C(graphite) + O2(g) CO2(g)

Gorxn = Gf

o(CO2) - [Gfo(graph) + Gf

o(O2)]

Gorxn = -394.4 kJ - [ 0 + 0]

Note that free energy of formation of an element in its standard state is 0.

Gorxn = -394.4 kJ

Reaction is product-favored as expected.

GGoorxnrxn = = GGff

oo )products( - )products( - GGffoo )reactants( )reactants(

Free Energy and Temperature

2 Fe2O3(s) + 3 C(s) 4 Fe(s) + 3 CO2(g)

Horxn = +467.9 kJ So

rxn = +560.3 J/K

Gorxn = 467.9 kJ - (298K)(0.560kJ/K) = +300.8 kJ

Reaction is reactant-favored at 298 K

At what T does Gorxn just change from (+) to (-)?

i.e. what is T for Gorxn = 0 = Ho

rxn - TSorxn

If Gorxn = 0 then Ho

rxn = TSorxn

so T = Ho/So ~ 468kJ/0.56kJ/K = 836 K or 563oC

Go 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) Gorxn = +742 kJ

3/2 C(s) + 3/2 O2 (g) 3/2 CO2(g) Gorxn = -592 kJ

with a thermodynamically allowed reaction:

Overall : Fe2O3(s) + 3/2 C(s) 2 Fe(s) + 3/2 CO2(g)

Gorxn= +301 kJ @ 25oC

BUT Gorxn < 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 Horxn = -20 kJ

Sorxn = +34 J/K

Gorxn = -30 kJ at 37oC

Thermodynamics and Keq

• Keq is related to reaction favorability.

• If Gorxn < 0, reaction is product-favored.

• Gorxn 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 ?

Grxn versus Gorxn

Under any condition of a reacting system, we can define Grxn in terms of the REACTION QUOTIENT, Q

Grxn = Gorxn + RT ln Q

At equilibrium, Grxn = 0. Also, Q = K. Thus

If Grxn < 0 then reaction proceeds to rightIf Grxn > 0 then reaction proceeds to left

Gorxn = - RT lnK

2 NO2 N2O4

Gorxn = -4.8 kJ

• pure NO2 has Grxn < 0.

• Reaction proceeds until Grxn = 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 (2)

N2O4 2 NO2

Gorxn = +4.8 kJ

• pure N2O4 has Grxn < 0.

• Reaction proceeds until Grxn = 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.



Keq is related to reaction favorability and so to Go

rxn.

The larger the value of Gorxn the larger the

value of K.

Gorxn = - RT lnK

where R = 8.31 J/K•mol

Calculate K for the reaction

N2O4 2 NO2 Gorxn = +4.8 kJ

Gorxn = +4800 J = - (8.31 J/K)(298 K) ln K

Gorxn = - RT lnK

lnK = -4800 J

)8.31 J/K()298K( = - 1.94


When Gorxn > 0, then K < 1 - reactant favoured

When Gorxn < 0, then K >1 - product favoured

K = 0.14

تُعادل ثابت و دما بین رابطه

12

12

1

2

303.2log

TT

TT

R

H

K

K o

سلوَلی ترمودینامیک

فصل پایان تمرینهای

• 4-6-8-10-14-16-18-20-24-28-32-34-36-38-40-42-44

CHAPTER 20

ELECTROCHEMISTRY

ماده اجزاء

ماده انواع

انْي- جر1-1-2لْي- پتانس1-1-3- مقاومت1-1-4يکْي- مدار اَلکتر1-1-5

RecallOxidation – 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.

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

Reducing agent/reductant – The substance that cause reduction of another substance and hence it is oxidised.

Oxidizing and reducing agents in direct contact.

Cu(s) + 2 Ag+(aq) Cu2+(aq) + 2 Ag(s)

Ag+(aq)Cu2+(aq)

Zn)s( Zn2+)aq( + 2e-

Cu2+)aq( + 2e- Cu)s(

Zn strip inserted into CuSO4 solution

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

• 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.

C 1J 1

V 1

Cell EMFCell 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 Ecell.

• 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 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 = Eo

red(cathode) - Eored(anode)

• Standard reduction potentials, Ered are measured relative to the standard hydrogen electrode (SHE).

Zn+2 SO4-

2

1 M HCl

Anode

0.76

1 M ZnSO4

H+

Cl-

H2 in

Cathode

• In a voltaic (galvanic) cell (spontaneous) Ered(cathode) is more positive than Ered(anode) since

• A positive E indicates a spontaneous process (galvanic cell).

• A negative E indicates a nonspontaneous process.

Spontaneity of Redox Spontaneity of Redox ReactionsReactions

anodecathode redredcell EEE

EMF and Free-Energy Change• We can show that

G 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

• Since n and F are positive, if G > 0 then E < 0.

Spontaneity of Redox Spontaneity of Redox ReactionsReactions

nFEG

J/V·mol 96,500Cmol 500,961 F

Effect of concentration

QlnRTGG o Since Go = -nFEo and G = -nFE

QlnnF

RTEE o

QlognF

RT303.2EE o

Qlogn

05916.0EE o at 25oC

Nernst equation

Qlogn

05916.0EE o

Use the Nernst equation to:

- find the EMF produced by a cell under non- standard 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: Ni)s( Ni2+)aq( + 2e- Eored = -0.28V

Cathode: Ni2+)aq( + 2e- Ni)s( Eored = -0.28V

Eocell = Eo

red)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: Ni)s( Ni2+)aq, dil( + 2e-

Cathode: Ni2+)aq, conc( + 2e- Ni)s(

Ni2+)aq, conc( Ni2+)aq, dil(

conc2

dil2

o

]Ni[

]Ni[log

n

05916.0EE

(00.1)

(1000.1)log

2

05916.0(V0)E

3

V0887.0E

NOTE:NOTE:

When the concentrations in the 2 compartments become equal,

Q = 1 and E = 0 V.

EMF and EquilibriumWhy does the emf drop as a voltaic cell discharges?

As reactants are converted to products, Q increases.

Qlogn

05916.0EE o Look at Nernst equation:

Eventually E = 0 V.

Since G = -nFE, G = 0 kJ/mol

equilibrium!

i.e. when E = 0 V, equilibrium no net reaction

At equilibrium:

E = 0 V and Q = K

Qlogn

05916.0EE o

Klogn

05916.0E0 o

05916.0

nEKlog

o

The equilibrium constant can be calculated for a redox reaction as follows:

E نيست جمع قابل

FeFeFe V 0.4402V 0.7713

؟771/0+440/0-=331/0

-0.036 /

///

///

3

3223

3223

FeFe

FeFeFeFeFeFe

FeFeFeFeFeFe

E

nFEnFEnFE

GGG

نمودار زیر را تکمیل نموده و یک دمیده شود چه گونه هایی از نیتروژن pH در محلول اسیدی با NOدر صورتی که گاز

در محلول ایجاد می گردند

مفید کار بیشترین

i=0

كاربردهاي الكتروشيمي

Batteries Fuel cells

Manufacturing of chemicals

Electroplating and refining

of metals

Study and control for corrosion

Study of redox reactions

Bioelectrochemistry: study of electron

transfer in biological regulations of

organisms

سيستمهاي انواعالكتروشيميايي

G<0گاَلواني

) خوردگی فلزات زدن زنگ سوختی، پیل باتری،کاتدی) محافظت ، فلزات

G>0اَلكتروَلْيتي

( فلزات، ( آبکاری ، اَلکتروَلیز مواد اَلکتریکی تجزیهشیمیایی مواد توَلید

واكنش آند

واكنش كاتد

قطب - قطب +

اكسْيداسْيون

احْيا كاتد آند پْيل اَلكتروَلْيتي

اكسْيداسْيون

احْيا آند كاتد گاَلواني پْيل

آب الکترولیز

زمان تارْيخچه توَلْيد باتري به

سه حدود يُعنْي انياشکانحکومت

ح ْيالد حضرت مسْياز م پْيش قرن

باز مْي)ع( .گردد

ن ْي که توسط محققين باترْيا

در اطراف 1993 در سال يشْياطر

خواجه ربو به نام يبغداد در محل

يباتردا شد هم اکنون با نام ْيپ

. شودي مْيي در جهان شناسابغداد

له آهني : ميقطب منف

قطب مثبت : استوانه مس

يوه هايت : آب ميالکترولترش مزه

ولت5/1-2ولتاژ :

تاريخچه كشف باتري تاريخچه كشف باتري

http://www.corrosion-doctors.org/Batteries/historyold.htm

Anode: Zn Zn2+ + 2e-

Cathode: 2MnO2 + 2H2O +2e- 2MnOOH + 2OH-

Electrolyte: Zn2+ 2NH4Cl +2OH- Zn(NH3)Cl2 + 2H2O

2MnO2 + Zn + 2NH4Cl 2MnOOH + Zn(NH3)Cl2

Modern Zinc-Manganese

battery

Zn-container

Carbon rod

MnO2 paste (cathode)

Gas space

Gel electrolyte

Georges Leclanché (1839-1882)

Primary batteries

Leclanché’s battery )1866(

Seal

Zn-container

MnO2 paste (cathode)

Carbon rod

NH4OH electrolyte

Sir William Grove 1811–1896

Grove’s fuel cell (1839)

O2 H2

4H+ + 4e- 2H2

2H2O - 4e- O2 + 4H+

Electrolyte frame Bipolar plate

Fuel Cells performance improving

Raising the current:

• Increasing the temperature

• Increasing the area of eelectrode electrolyte interface

• The use of catalyst

Raising the voltage:

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

Connection of cells in seriesCell stack

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

ANODE

CATHODEELECTROLYTE

Bipolar electrode

Anode catalystCathode catalyst

O2

H2

Stack of several hundred

فلزات استخراج

Electrolysis of NaCl solution

Battery

Salt solution consists of Na+ and Cl– ions

CATHODE

ee

2Na+ + 2e– = 2Na E= -2.74 O2 +4e – + 2H2O = 4OH- E= -0.41 2H2O = 2H+ +2e – + ½ O2 E=1.23

2 Cl– = Cl2 + 2e– E=1.35

reductionoxidation

ANODE

مواد تولید

Production of aluminum

AlF63– + 3 e– Al + 6 F– . . . Cathode

2 Al2OF62– + C(s) + 12 F– 4 AlF6

3– + CO2 + 4 e– . . . Anode

2 Al2O3 + 3 C 4 Al + 3 CO2 . . . Overall cell reaction

Hall and Heroult tried to mix about 5% alumina in their molten cryolite, and obtained Al metal. This is the Hall process.

Charge required for each mole Al = 3 F

Energy required = 3 F E

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.

Electrolysis of acid solutionBattery

Solutions containing H+ and SO42– ions

CATHODE

ee2H+ + 2e– = H2

H2O = ½ O2 + 2e– + 2 H+

Charges required to produce 1 mole H2 and ½ moles O2 = 2F

Energy required = 2 F E

reductionoxidation

ANODE

Electrolysis of H2SO4 solutionPure 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+ E o = -1.23 V (observed)2 SO4

2– = [SO3O–OSO3]2– + 2 e– E o = 2.01 V (not observed)

Electrolysis of H2SO4 solution

BatteryE o = 1.23 V 2 H2O (l) = 4 e– + O2 (g) + 4 H+ E o = 2.01 V 2 SO4

2– = [SO3O–OSO3]2– + 2 e–

Solution consists of H+ and SO42– ions

CATHODE

ANODE

ee2H+ + 2e = H2

reductionoxidation

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?

CoatingUse sacrifice electrode

Cathodic protection of an underground pipe.

فصل پاْيان تمرْينهاي

و 34و 32و30و 28و 26و 24و 6و 4و 2و 50و 48و 46و 44و 42و 40و 38و 36و 66و 64و 62و 60و 58و 56و 54و 52.75و 74و 72و 68

The Transition Elements and Coordination

Compounds

Complex Ions and Coordination Compounds

نوزدهم • سده اواخر شیمیداناندر پیوند ماهیت درک برای میالدی

مرتبه برکیبات یا موَلکوَلی ترکیبات . بودند روبرو دشواری با باالتر

فرمول با ترکیبی تشکیلCoCl3.6NH3 به بود کننده گمراه

که فوق مورد مثل مواردی در ویژهوجود CoCl3ترکیب تنهایی به

ندارد.سال توضیح 1893در برای ای نظریه ورنر آَلفرد

. داد ارائه را ترکیبات گونه این


A pair of electrons on the oxygen atom of H2O forms a coordinate covalent bond to Fe2+.


• 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)6

4- 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 ringsany number of atoms in the ringmost 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.


• The name of the cation precedes the name of the anion.

For example,

K4[Fe(CN)6] is named

potassium hexacyanoferrate(II)

cation anion


• The name of the cation precedes the name of the anion.

For example,

[Co(NH3)6]Cl3 is named

hexaamminecobalt(III) chloride

cation anion


• 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


• 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


• 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, Br- bromo

Carbonate, CO32- carbonato

Cyanide, CN- cyano

Oxalate, C2O42- oxalato

Sulfate, SO42- sulfato

Oxide, O2- oxo


• 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 ammine

Carbon monoxide, CO carbonyl

Water, H2O aqua


• 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


• 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 Cuprate

Gold Aurate

Iron Ferrate

Lead Plumbate

Silver Argenate

Tin 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.

Isomers of CoCI2(en)2+

Covalent bond formation between atoms X and Y.

• Fe2+ : [Ar], 4s, 3d6, 4p

d3

s4

p3

Crystal Field Theory )CFT(

Fe 2+ : [Ar], 3d6,4s

1s+3p+2dsp3d2

Octahedral Geometry.

The colour can change depending on a number of factors e.g.

1. Metal charge2. 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)6

3+.

Return to slide 47

Physical phenomenon

فصل پاْيان تمرْينهاي

و 18و 16و 14و 13و 6و 4و 2.28و 22و 20

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 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:

XAZ

symbol of theelement

mass number(total # of nucleons)

atomic number(# of protons)

e.g., K1939 Potassium-39; nucleus

contains 19 protonsand 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 DecayThe 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

Num

ber

of n

eutr

ons

(A–Z

)Unstable region(too many neutrons;spontaneous betaproduction)

202 80 Hg (1.53:1 ratio)

110 48 Cd(1.29:1 ratio)

1:1

neutro

n-to-p

roto

n ratio

Sta

ble

nucl

ides

in th

e

zone

of s

tabi

lity

63Li (1:1 ratio)

Unstable region(too many protons;spontaneous positronproduction)

Number of protons (Z)20 40 60 80 100

20

40

60

80

100

120

00

• 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: 2He2+, 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

4

• 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: +1e

– in positron emission, a proton in the nucleus is effectively transformed into a neutron

0

19K 18Ar + +1e40 40

0

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:

95Am 93Np + 2He241 237 4

Uranium-237 decays by emission:

92U 93Np + -1e237 237 0

Balancing Nuclear Equations(cont.)

Carbon-11 decays by + emission

6C 5B + +1e11 11 0

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

• In the shorthand used by nuclear chemists, this reaction would be written:

1

7N + 2He 1H + 8O14 17

7 N (,p) 8O14 17

4

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 timezero 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

NNo

= ( 12 ) n

Half-LifeThe half-life is the amount of time during which the radioisotope decaysby 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

• 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

6C 7N + -1e 1414 0

Biomedical Applications

Effects of Radiation

Penetrating Powerof Radiation Types

paper aluminum lead

Chemical Effects of Radiation

High energy radiation produces not only ions along its penetration track, but freeradicals as well.

primary radiation eventH2O + radiation H2O+ + e- (aq)

secondary chemical processesH2O+ + H2O H3O.+ + .OH

e- (aq) + H2O .H + OH-

single unpaired electron characteristicof a free radical is shown as a dot onthe appropriate atom

Chemical Effects of Radiation (cont.)

Free radicals may abstract a hydrogenatom from a donor biomolecule, whichthen produces a biomolecule freeradical.

.OH + H-R-NH2HOH + .R-NH2

Biomolecule free radical may nowcombine with itself or anotherbiomolecule. If that biomolecule is anenzyme or a nucleic acid, normalfunction may be severely altered andcellular activity adversely affected.

Protection from Radiation

Minimize exposure to high-energyradiation: 1) use a radiation-absorbingbarrier, 2) maximize the distance ofseparation, and 3) limit the time ofexposureinverse-square law

I ≈ 1d2

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 (Rntgen equivalent for man)– Takes into acccount the relative biological effectiveness

(RBE) for different kinds of radiation– RBE=1 for x, β, and γ rays and 10 for α-paritcles, protons,

and neutronsrads x RBE = rems

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 β-emitter

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

PositronEmission

Tomography(PET)

Tomograms

NormalBrain

Alzheimer’sBrain

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

• 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

92U + 0n [ 92U*] 36Kr + 56Ba + 3 0n235 1 236 92 141 1

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 +1e– 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

1 4 0

what is thermodynamics? به مجموعه روشهای ریاضی که به ما کمک می...

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