vodonik
TRANSCRIPT
![Page 1: vodonik](https://reader030.vdocuments.pub/reader030/viewer/2022012321/55cf9d50550346d033ad1899/html5/thumbnails/1.jpg)
Vodonik je najrasprostranjeniji element u svemiru. Zvezde su sastavljene uglavnom od vodonika (maseni udeo vodonika u svemiru je oko 90%)
Po broju atoma u Zemljinoj kori vodonik je na trećem mestu posle kiseonika i silicijuma, - po masi na jedanaestom mestu.
Elementarni vodonik nalazi se samo u najvišim slojevima atmosfere i kao sastavni deo vulkanskih gasova.
Engleski hemčar Henry Cavendish (1731–1810) izolovao je 1766 godine čist vodonik
‘hydro genes’ - onaj koji formira vodu
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Položaj vodonika u periodnom sistemu elemenata
1H 1s1
1 grupa 17 grupa
1s1
X X
Oksidaciono stanje: +1 -1
H (1s1) H+ (1s0) H¯ (1s2)
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Fizičke i hemijske osobine vodonika
Kovalentni radijus
(nm)
Jonski radijus (nm) Tt (ºC) Tk (ºC)
Energija jonizacije
(eV)
Elektro-
negativ-
nost
Redoks
potencijal
(V)
Energija
veze H2
(kJ/mol) H¯
0,029 0,208 -259 -253 13,6 2,1 0,0 435
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Dobijanje vodonika:1. Laboratorijsko dobijanje vodonika
1.1. Reakcija metala i kiseline:
Zn(s) + 2H+ Zn2+ + H2(g)
O O+1
2H+ + 2e- H2(g)
E02H+/H2 = 0,0 V [a(H+) = 1 mol/dm3]
Zn2+ + 2e- Zn(s)
E0Zn2+/Zn =-0,76 V
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u vodi
2H+(1,00.10-7 mol/dm3) + 2e- H2(g) (101,325 kPa)
E = E0 + 0,059 V . log[H+] = -0,41 V
2Na(s) + 2H2O 2Na+ + 2OH- + H2(g)O O+1
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1.2. Reakcija hidrida metala i vode:
2Al(s) + 6H2O + 2OH- 2Al(OH)4 + 3H2(g)
Zn(s) + 2H2O + OH- Zn(OH)3 + H2(g)
1.3. Reakcija alkalnih hidroksida i nekih metala (koji imaju negativan redoks-potencijal)
2H2O + CaH2(s) 2H2(g) + Ca2+ + 2OH-+1 -1 O
H+ + H- H2(g)
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1.4. Elektroliza vode:
Katoda: 4H2O + 4e- 2H2(g) + 4OH-
Anoda: 4OH- O2(g) + 2H2O + 4e-
Ukupna reakcija: 2H2O 2H2(g) + O2(g)
redukcija
oksidacija
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H2(g) se izdvaja na negativnoj elektrodi (katoda)
O2(g) se izdvaja na pozitivnoj elektrodi (anoda)
Stehiometrijski odnos dobijenih gasova je 2:1(H2:O2)
katodaanoda
MOH
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2. Industrijsko dobijanje vodonika
2.1. Krekovanje (piroliza) ugljovodonika:
C2H6(g) C2H4(g) + H2(g)
CH4(g) + H2O(g) CO(g) + 3H2(g) rH = 214,4 kJ/mol
CH4(g) + 2O2(g) CO2(g) + 2H2O(g) rH = -801,6 kJ/mol
1100oC
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2.2. Redukcija vodene pare sa ugljenikom:
C(s) + H2O(g) CO(g) + H2(g) rH = 131,25 kJ/mol
C(s) + O2(g) CO2(g) rH = -393 kJ/mol
CO(g) + H2O(g) CO2(g) + H2(g)
Vodeni gas – CO + H2
rH = 41,4kJ/mol
t = 450oC
1100oC
Fe2O3
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2.3. Elektroliza vodenog rastvora NaCl:
2 NaCl + 2 H2O → 2 Na+ + 2 OH¯ + H2(g) + Cl2 (g)
H2 je veoma čist i koristi se za hidrogenizaciju ulja
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Osobine vodonika:
Na sobnoj temperaturi vodonik je gas
- bez boje
- bez mirisa i ukusa
Dvoatomni molekul
H2(g) 2H(g) rH = 435,1 kJ/mol
H H
Tt (ºC) Tk (ºC)
-259 -253
- najjača jednostruka veza
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1s 1s
1s
1s
HH
en
erg
ija
H H
red veze = 1
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Jedinjenja vodonikaOksidaciono stanje: +1 -1
H (1s1) H+ (1s0) H¯ (1s2)
1. Jedinjenja vodonika sa negativnim oksidacionim stanjem (-1):
HIDRIDI
HIDRIDI SONOG KARAKTERA (jonski hidridi)
METALNI HIDRIDI
KOVALENTNI HIDRIDI
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-Hidridi jonskog tipa2M(l) + H2(g) 2MH(s)
M(l) + H2(g) MH2(s)
p = 101,325 kPa
t = 300 – 700oC
LiH
NaH
KH
RbH
CsH
CaH2
SrH2 BaH2
-u reakciji sa vodom izdvaja se vodonik
Primer:
2NaH + 2H2O → 2NaOH + H2(g)
H- + H2O H2(g) + OH-
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LiH
SrH2
BaH2
} vrlo burna reakcija sa vodomNaH
CsH
} burna reakcija sa vodom
CaH2 } umerena reakcija sa vodom
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4LiH + AlCl3 Li(AlH4) + 3LiCl
M + Al + 2H2 M(AlH4)
-Hidridi metalnog karaktera
-hidridi lantanida i aktinida
najvažniji hidridi sonog karaktera su NaH, LiH i CaH2
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-Kovalentni hidridi
- hidridi bora (BH3, B2H6…..)
- hidridi aluminijuma (AlH3)
- hidridi berilijuma (BeH2)
3LiH + AlCl3 AlH3(s) + 3LiCl
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2. Jedinjenja vodonika sa pozitivnim oksidacionim stanjem (+1):
- katalizator Pt- temperatura 600oC eksplozija - praskavi gas
2H2(g) + O2(g) 2H2O(g) rH = -483,6kJ/mol
O2
H2
Daniellov plamenik koristi se za autogeno zavarivanje t = 2700 oC
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makroskopski izgled
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T (ºC) V (cm3) m (g)
10 1 0,997
4 1 1,000
0 1 0,917
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t = 500oC
N2(g) + 3H2(g) 2NH3(g) rH = -92 kJ/mol
o o -3 +1
CO(g) + 2H2(g) CH3OH(g)
CuO9s) + H2(g) Cu(s) + H2O
o
o
+2
+1
-2 +1 +1ZnO
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Upotreba vodonika:
u industriji za sintezu amonijaka
hidrogenizaciju ulja i ugljenika
za sintezu HCl
vodeni gas – važno gorivo
autogeno zavarivanje
za punjenje balona
redukciono sredstvo
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Izotopi vodonika
2
H (D)1
1
H1
3
H (T)1
protijum
deuterijum
tricijum
- protijuma u vodi ima 5000 puta više u odnosu na deuterijum i 1 x 1017 puta više u odnosu na tricijum
Kw(H2O) = 1x10-14 mol2/dm6
Kw(D2O) = 0,2x10-14 mol2/dm6