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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Oxidation of ammonia to nitrogen and steam
    4       +       3 2       +         6
Ammonia
 +
Oxygen
  
Reactants
  
Nitrogen
 +
Steam
 
Products
  
Products – Reactants
ΔfH⦵
  
ΔfH⦵
 
Σf-reactH⦵
  
ΔfH⦵
  
ΔfH
 
 
Σf-prodH⦵
  
Σf-prodH⦵ - Σf-reactH⦵ = ΔrH⦵
(-46.1 x 4)
+
(0.0 x 3)
=
-184.44
 
(0.0 x 2)
+
(-241.8 x 6)
=
-1,450.9
 
-1,450.9 - -184.4 = -1,266.5 kJmol-1
                             
S⦵
  
S⦵
 
ΣreactS⦵
  
S⦵
  
S
 
 
ΣprodS⦵
  
ΣprodS⦵ - ΣreactS⦵ = ΔrS⦵
(0.192 x 4)
+
(0.205 x 3)
=
1.385
 
(0.192 x 2)
+
(0.189 x 6)
=
1.516
 
1.516 - 1.385 = 0.131 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
  
ΔrG⦵   = ΔrH⦵ – (T298 x ΔrS⦵)   =   -1,266.5– (298 x 0.131)  =
-1,305.5kJmol-1
ΔrH⦵
=
 -1,266.5 kJmol-1 Negative value: the reaction is exothermic
ΔrS⦵
=
 +0.131 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG⦵ 298K
=
 -1,305.5 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
 >10100 Value is greater than 1: the reaction proceeds to the right
No equilibrium temperature: this reaction is feasible at all temperatures
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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