Chuong11- Dien Hoa

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  • 8/3/2019 Chuong11- Dien Hoa

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    CHNG 11

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    Phan ng oxy hoa kh (O K)

    Phan ng trong o co s trao

    oi electron gia cac nguyen tcua nhng nguyen to tham gia phan

    ng lam thay oi so oxy hoa cac

    nguyen to.

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    Qua trnh cho electron goi la quatrnh oxy hoa, chat cho electron goila chat kh(chat b oxy hoa).

    V du:

    Zn 2e' Zn+2 Qua trnh nhan electron goi la

    qua trnh kh, chat nhan electron

    goi la chat oxy hoa. V du:

    Cu+2 + 2e ' Cu

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    Phn ng tng quat:

    Qt oxh: hI ' OxI + neQt kh: OxII + ne ' hIIPt oxh kh: hI + OxII ' OxI +

    KhII

    Cap oxy hoa kh: OxI/KhI , OxII/KhII

    Vdu:

    Qt oxh: Zn ' Zn2+ + 2e

    Qt kh: Cu2+ + 2e ' Cu

    Pt oxh kh: Zn + Cu2+ Zn2+ + Cu

    Pt phan t: Zn + CuSO4 ZnSO4 + Cu

    Cap oxy hoa kh: Zn2+/Zn; Cu2+/Cu

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    Nguyen tac 1: Tong so electron cho cua chat kh

    phai bang tong so electron chat oxyhoa nhan vao.

    Cac bc tien hanh can bang. Bc 1: Xac nh s thay oi so oxy

    hoa cua cac chat. Bc 2: Lap phng trnh electron ion,

    vi he so sao cho ung qui tac tren.

    Bc 3: Thiet lap phng trnh ion cua

    phan ng.

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    Vdu:Al + CuSO4 p Al2(SO4)3 + Cu

    Al - 3e p Al+3

    Cu+2

    + 2e p Cu2Al + 3Cu+2 = 2Al+3 + 3Cu

    2Al + 3CuSO4 p 2Al2(SO4)3 + 3Cu

    X2

    X3

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    Nguyen tac 2:

    oi vi phan ng O K xay ra trongmoi trng acid neu dang Ox cua chatOx co cha nhieu nguyen t Oxy hn

    dang kh cua no th phai them H+

    vaove tr ai (dang Ox) va them nc vaove phai (dang kh).

    Neu dang kh cua chat Kh cha t

    nguyen t Oxy hn dang Ox cua no ththem nc vao ve tr ai (dang Kh) va H+

    vao ve phai (dang Ox).

    Thieu O ben nao, them H2O ben o,ben kia them H+

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    Vdu:

    OHSOKKNOMnSOSOHKNOKMnO 242344224 p

    p

    p

    32

    2

    4

    2

    5

    NOeNO

    MneMnO

    OHMnHeMnO 22

    4 485 p

    p HNOOHeNO 22

    322

    OHSOKKNOMnSOSOHKNOKMnO

    OHNOMnHNOMnO

    242344224

    2324

    352352

    352652

    !

    !

    X2

    X5

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    Nguyen tac 3:

    Phan ng O K xay ra trong moitrng base, neu dang Ox cua chatOx cha nhieu Oxy hn dang kh th

    phai them nc vao ve tr ai, OH-vao ve phai.

    Neu dang Kh cua chat Kh cha t Oxyhn dang Ox cua no th phai themOH- vao ve trai, nc vao ve phai.

    Thieu O ben nao them OH- ben o,ben kia la H

    2

    O.

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    Vdu:

    X1

    X2

    OHKClCrOKKOHCrClKClO24233

    p

    ! OHClOHeClO 636 23

    OHCrOOHeCr 22

    4

    3 483 !

    OHCrOClOHCrClO2

    2

    4

    3

    3522 !

    OHCrOKKClKOHCrClKClO 24233 527102 !

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    Nguyen tac 4:

    Phan ng O-K trong moi trngtrung tnh. Neu dang Ox cua chat Oxcha nhieu nguyen t Oxy hn

    dang Kh cua no th phai themnc vao ve trai, OH- vao ve phai.

    Neu dang Kh cua chat Kh cha tnguyen t Oxy hn dang Ox cua no

    th phai them nc vao ve tr ai, H+vao ve phai.

    Them nc ve trai het, ve phai:- +

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    Vdu:

    X2

    X3

    KOHKNOMnOOHKNOKMnO p 32224

    ! OHMnOOHeMnO 423 224

    ! HNOOHeNO 22

    322

    ! HOHNOMnOOHNOMnO 6832732

    32224

    ! OHNOMnOOHNOMnO 23232

    32224

    KOHKNOMnOOHKNOKMnO 23232 32224 !

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    Phan ng O K va dongien

    ieu kien bnh thng, phan ng O K xay racung mot ni th hoa nang se bien thanh nhietnang.

    ieu kien ac biet phan ng O K xay ragian tiep hai ni khac nhau th hoa nang sebien thanh ien nang (qua day dan).e-

    Chat kh

    e-

    e-

    Cha

    t oxhAnode Cathode

    Mang ngan

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    Nguyen to galvanic(1780): La thiet b chuyen hoa

    nang sang ien nang.Cau tao gom hai thanh kimloai, nhung trong dung dchmuoi cua no, noi vi

    nhau qua si day dan kimloai.

    Hai thanh kim loai nay mot

    thanh co tnh kh manhhn e cho e mot thanh

    Luigi Galvani (Italia)

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    Cathode (+), xay raqua trnh kh

    Anode (-) , xay raqua trnh oxy hoa

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    ien cc kem:Zn 2e p Zn+2 goi la am cc (Cathode)

    ien cc ong:Cu+2 + 2e p Cu goi la dng cc (Anode)

    Tc la am cc xay ra qua trnh Oxy hoa,Zn la chat Kh. dng cc xay ra qua trnhkh, Cu la chat Ox.

    Phng trnh cua galvanic:Zn+Cu+2 = Zn+2 + Cu

    Ngi ta ky hieu nguyen to ganvanic:

    Hay

    Tong quat:

    CuCuSOZnSOZn44

    CuCuZnZn 22

    IIIIII

    MddMddMM

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    The ien cc N (V), hay con goi lathe Oxy hoa Kh, hay la ban thephan ng, la mot ai lng khong

    the o tr c tiep, ma phai so sanhvi mot ien cc chuan. Ngi ta chon Hydro lam ien cc

    chuan:

    2H+(dd) + 2e p H2 (k), ien cc laplatinum.Quy c: N0H2 = 0 (V). (The ien cc

    tuyet oi cua no c chng 4.4 4.6

    V)

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    Phng trnh Nernst:

    Kh ne p Ox, N

    Vi a la hoat o. Hoat o cua cac kimloai tinh khiet (va ca long tinh khiet) coinh bang 1.

    Vi dung dch that (s dung C) nhieto 298K, ta co (R=8.31, T=298,F=96500):

    Kh

    Ox

    a

    a

    nF

    RTln

    0!NN

    ][

    ][lg

    059.000

    Kh

    Ox

    n! NN

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    N phu thuoc vao ban chat chat thamgia qua trnh ien cc (N0, n) nhiet oT, nong o chat tham gia qua trnhien cc C.

    Ta co:UG = -nFN, hayUG0 = -nFN0

    Sau ay la bang the ien cc tieuchuan cua mot so ban phan ng(The Ox-Kh).

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    Banphan ng1bar,298K, Ci = 1M

    N0 (V)

    Li+(aq) + e Li(s) 3.05

    K+(aq) + e K(s) 2.93

    Ba2+(aq) + 2e Ba(s) 2.91

    Ca2+(aq) + 2e Ca(s) 2.76

    Na+(aq) + e Na(s) 2.71

    Mg2+(aq) + 2e Mg(s) 2.38

    Be2+(aq) + 2e Be(s) 1.85

    Al3+(aq) + 3e Al(s) 1.68

    Ti3+(aq) + 3e Ti(s) 1.21

    Mn2+(aq) + 2e Mn(s) 1.18

    Sn(s) + 4H+ + 4e SnH4(g) 1.07

    2 H2O(l)+2eH

    2(g)+2OH(aq) 0.83

    Zn2+(aq) + 2e Zn(s) 0.76

    Cr3+(aq) + 3e Cr(s) 0.74

    Fe2

    +(aq) + 2e Fe(s) 0.44

    Cr3+(aq) + e Cr2+(aq) 0.42

    Sn2+(aq) + 2e Sn(s) 0.13

    2H+(aq) + 2e H2(g) 0.00

    Sn4+(aq) + 2e Sn2+(aq) +0.15

    Cu2+(aq) + e Cu+(aq) +0.16

    SO42(aq) + 4H+ + 2e

    2H2O(l) + SO

    2(aq)

    +0.17

    Cu2+(aq) + 2e Cu(s) +0.34

    O2(g)+2H

    2O(l)+4e 4OH(aq) +0.40

    SO2(aq)+4H++4eS(s)+ 2H

    2O +0.50

    Cu+(aq) + e Cu(s) +0.52

    I2(s) + 2e 2I(aq) +0.54

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    MnO4(aq) + 2H

    2O(l) + 3e

    MnO2(s) + 4 OH(aq)

    +0.59

    S2O32

    + 6H+ + 4e 2S(s) +3H

    2O

    +0.60

    O2(g) + 2H+ + 2e H

    2O

    2(aq) +0.70

    Fe3+(aq) + e Fe2+(aq) +0.77

    Hg22+(aq) + 2e 2Hg(l) +0.80

    Ag+(aq) + e Ag(s) +0.80

    NO3(aq) + 2H+(aq) +e

    NO2(g) + H

    2O(l)

    +0.80

    Hg2+(aq) + 2e Hg(l) +0.85

    MnO

    4

    (aq) + H+

    + e

    HMnO4

    (aq)+0.90

    2Hg2+(aq) + 2e Hg22+(aq) +0.91

    MnO2(s) + 4H+ + e Mn3+(aq)

    + 2H2O

    +0.95

    Br2(aq) + 2e 2Br(aq) +1.09

    2IO3(aq) + 12H+ + 10e I

    2(s)

    + 6H2O

    +1.20

    ClO4(aq) + 2H+ + 2e

    ClO3(aq) + H

    2O

    +1.20

    O2(g) + 4H+ + 4e 2H

    2O +1.23

    MnO2(s) + 4H+ + 2e

    Mn2+(aq) + 2H2O

    +1.23

    Cl2(g) + 2e 2Cl(aq) +1.36

    Cr2O7

    2(aq) + 14H+ + 6e

    2Cr3+(aq) + 7H2O

    +1.36

    MnO4(aq) + 8H+ + 5e

    Mn2+(aq) + 4H2O

    +1.51

    2HClO(aq) + 2H+ + 2e Cl2(g)+ 2H

    2O

    +1.63

    MnO4(aq) + 4H+ + 3e

    MnO2(s) + 2H

    2O

    +1.70

    H2O

    2(aq) + 2H+ + 2e 2H

    2O +1.76

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    The hieu cc ai xuat hien gia haicc ca nguyen to ganvanic goi la scien ong cua nguyen to ganvanic,khi ma nguyen to galvanic hoat ong T

    N.

    Khieu:

    Sc ien ong tieu chuan cuanguyen to galvanic. E0 o p = 1 atm, CM

    (hay a) = 1, 298K.

    NN!E

    000

    E NN!

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    aKh1 + bOXH2' cOXH1 + dKh2

    -(G = A = nFE

    b

    2

    a

    1

    d

    2

    c

    10

    OXHKh

    KhOXHlnRTGG (!(

    b

    2

    a

    1

    d

    2

    c

    1

    OXHKh

    KhOXH

    lnRTKlnRTnFE !

    b

    2

    a

    1

    d

    2

    c

    1

    OXHKh

    KhOXHln

    nF

    RTKln

    nF

    RTE !

    KlnnF

    RTE0 !

    (G0

    = -nFE0

    ba

    dc

    OXHKh

    KhOXH

    nF

    RTEE

    21

    210ln!

    cd

    sp

    nF

    RT

    EEln

    0!

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    Vduviphan ng trongnguyen to

    galvanic:Zn + Cu+2 = Zn+2 + Cu

    ViN+ lacuacap Cu+2/Cu vaN- la

    cuacap Zn+2

    /Zn, taco

    2

    2

    ln

    2

    0

    //

    !

    Cu

    Zn

    ZnCuZnCu

    C

    C

    F

    RTEE

    V...EZn/Cu

    1176303370000

    !!!

    NN

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    3324FeCeFeCeXet phan ng:

    34CeeCe

    23FeeFe N

    o

    =1.700V

    No=0.767V

    c tao thanh bi 2 ban phan ng sau

    V No cua cerium ln hn nen no la chat Oxy hoa.Ta co

    (0.767)-1.700-E ooo !!

    NN

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    Trong nguyen to galvanic co:

    ]][Ce[Fe

    ]][Ce[Feln

    nF

    RT---E

    42

    3300

    -

    !! NNNN

    Tai can bang, E = 0 va:

    1610K}

    C25,Klog05916.]][Ce[Fe

    ]][Ce[Feln

    F

    RT- o

    42

    33oo v!!

    NN

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    Xet caccap O-K: Ox1/Kh1 , Ox2/Kh2

    Kh1' Ox1 + ne ,N1

    Kh2'

    Ox2 + ne ,N2Khi troncaccapnay,se co phanng:

    Kh1 + Ox2 ' Ox1 + Kh2

    Phan ng xay ra theo chieu thuan khi:

    121212

    0 NNNN "!!( nFnFEG/

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    Quy tac xet chieu phan ng:

    Phan ng O K xay ra theo chieudang Ox cua cap O K co N ln hnse Ox dang Kh cua cap O K co N

    nho hn.

    Thc te co the dung N0 e xet.Nhng khi N0+ - N0- be qua thphai tnh toan tren N.