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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Dimerisation of NO2 to N2O4
           +      
Nitrogen dioxide
 +
Nitrogen dioxide
  
Reactants
  
Dinitrogen tetroxide
 
Products
  
Products – Reactants
ΔfH⦵
  
ΔfH⦵
 
Σf-reactH⦵
  
ΔfH⦵
  
 
 
Σf-prodH⦵
  
Σf-prodH⦵ - Σf-reactH⦵ = ΔrH⦵
(33.8 x 1)
+
(33.8 x 1)
=
67.60
 
(9.2 x 1)
=
9.2
 
9.2 - 67.6 = -58.4 kJmol-1
                             
S⦵
  
S⦵
 
ΣreactS⦵
  
S⦵
  
 
 
ΣprodS⦵
  
ΣprodS⦵ - ΣreactS⦵ = ΔrS⦵
(0.240 x 1)
+
(0.240 x 1)
=
0.480
 
(0.304 x 1)
=
0.304
 
0.304 - 0.480 = -0.176 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
  
ΔrG⦵   = ΔrH⦵ – (T298 x ΔrS⦵)   =   -58.4– (298 x -0.176)  =
-6.0kJmol-1
ΔrH⦵
=
 -58.4 kJmol-1 Negative value: the reaction is exothermic
ΔrS⦵
=
 -0.176 kJK-1mol-1 Negative value: the system becomes less dispersed
ΔrG⦵ 298K
=
 -6.0 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
 11.5 Value is greater than 1: the reaction proceeds to the right
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 332K (59°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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