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Chemical reactions and energy changes
reactants
If energy of reactants is greater
than energy of products, energy is
give out (released) during the
reaction: EXERGONIC
!"#$%&'(
products
If energy of reactants is less than
energy of products, energy is taken in
(absorbed) during the reaction:
ENDERGONIC
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reactants
INCREASING ENERGY
”!"#$%$&"'()”* +"#,$&
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Energy is released to
the surroundings
products
products
Energy is absorbed
from the surroundings
reactants
Reaction profile
Reaction profiles
transition state
following the course of a one-step exergonic
chemical reaction
(or activated complex)
e
n
e
r
g
y
bonds
breaking
activation
energy, Ea
reactants
bonds
forming
exergonic
reaction
e
n
er
g
y
reactants
exergonic
reaction
products
Course of reaction
Reaction profiles
following the course of a one-step endergonic
chemical reaction
products
e
n
er
g
y
products
Click for endergonic
exergonic
reaction
reactants
Replay Close window
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ATP
O
O
P
O
O
O
P
O
P
O
N
O
O
P
O
O
P
O
O
H
H
OH
H
H
O
N
NH
N
N
O
O
GTP
NH2
N
O
N
O
O
O
P
O
NH2
O
O-
H
H
OH
H
H
H
N
H
ATPase:
ATP
GTP
X
ADP + Pi
Nitrogen fixation
All living organisms need
nitrogen
• Nucleotides
• Amino acids
• Other bio-molecules
But, although earth atmosphere is 78% N2
most organisms can not use it, and need
fixed nitrogen - NH3, NO3, Urea etc.
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Fixed nitrogen can come from a
three sources
Fixed nitrogen can come from a
three sources
• Fertilizers
• Fertilizers
• Decaying bio-material
• Biological
Nitrogen Fixation
• Decaying bio-material
• Biological
#( %2!367
Nitrogen Fixation
!3&. 8(- - /2)02%
rhizobium
Nostoc
Fixed nitrogen can come from a
three sources
• Fertilizers +"",-$. +"/0"".* 1/(. 2$*"/
• Decaying bio-material
• Biological
Nitrogen Fixation
Azotobacter
Trichodesmium
2 3
N2+3H2->2NH
Fritz Haber (Nobel 1918) and Carl Bosch (1/2 nobel
1931)
Haber-Bosch process:
Mix gaseous H2 and N2 under:
* high temperature (~500oC)
* high pressure (~250 atmospheres, ~351kPa)
* In the presence of a catalyst (porous iron prepared by
reducing magnetite, Fe3O4).
(N2->NH3) $!+2),# 86+1 02*!1
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kJ/mol 92.4 !$!40+, 001()
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• Only by bacteria (both archaea and eubacteria)
• It is done by the nitrogenase multi-protein complex
(NifH, D and K). A large protein hetro-oligomer
• Although energetically favorable, it is bib-energetically
expensive due to the very stable triple N N bond
N2+10H++8e-+16ATP -> 2NH4++ H2+16ADP*
*) As measure in-vitro
• Other triple bond substrates cyanide (H!C N), azide (N3;
both to NH3), and acetylene (HC CH) among others evolutionary origin?
• The complex contain multiple metal centers, Fe-S, Mo
etc. Also alternative complexes
2 3
N2+3H2->2NH
Fritz Haber (Nobel 1918) and Carl Bosch (1/2 nobel
1931)
Haber-Bosch process:
Mix gaseous H2 and N2 under:
* high temperature (~500oC)
* high pressure (~250 atmospheres, ~351kPa)
* In the presence of a catalyst (porous iron prepared by
reducing magnetite, Fe3O4).
Biological nitrogen fixation:
* 1 atm
* ~ room temperature
* Catalyst? = enzyme - Nitrogenase
!" #$%$&'( #$($)*"
$+,&*"- #'./(-
1/2 N2->N
e
n
e
r
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activation
energy, Ea
3/2 H2->3H
N+3H>NH3
reactants
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exergonic
reaction
1/2 N2, 3/2 H2
NH3
Course of reaction
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Enzyme + Substrate ⇌ ES ! E + Product
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