Thermochemistry Synthlet


    
   or    Kelvin        
Haber ammonia synthesis
           +       3 2
Nitrogen
+
Hydrogen
 
Reactants
 
Ammonia
 
Products
 
ProductsReactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(0.0 x 1)
+
(0.0 x 3)
=
0.00
 
(-46.1 x 2)
=
-92.2
 
-92.2 - 0.0 = -92.2 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.192 x 1)
+
(0.131 x 3)
=
0.584
 
(0.192 x 2)
=
0.385
 
0.385 - 0.584 = -0.199 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG  = ΔrH – (T298 x ΔrS)   =   -92.2 – (298 x -0.199)  =
-33.0 kJmol-1
ΔrH
=
-92.2 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
-0.199 kJK-1mol-1 Negative value: the system becomes less dispersed
ΔrG 298K
=
-33.0 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
6.07 x 105 Value is greater than 1: the reaction proceeds to the right
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 464K (191°C)

Why Reactions Occur
Timeline of Structural Theory

© Mark R. Leach 1999-


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