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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Partial oxidation of methane to acetylene, H2 and CO
    6       +       2       +         2       +         10
Methane
 +
Oxygen
  
Reactants
  
Acetylene
 +
Carbon monoxide
 +
Hydrogen
  
Products
  
Products – Reactants
ΔfH⦵
  
ΔfH⦵
 
Σf-reactH⦵
  
ΔfH⦵
  
ΔfH
 
ΔfH
 
Σf-prodH⦵
  
Σf-prodH⦵ - Σf-reactH⦵ = ΔrH⦵
(-74.8 x 6)
+
(0.0 x 1)
=
-448.86
 
(226.7 x 2)
+
(-110.5 x 2)
+
(-110.5 x 2)
=
232.4
 
232.4 - -448.9 = 681.3 kJmol-1
                             
S⦵
  
S⦵
 
ΣreactS⦵
  
S⦵
  
S
 
S
 
ΣprodS⦵
  
ΣprodS⦵ - ΣreactS⦵ = ΔrS⦵
(0.186 x 6)
+
(0.205 x 1)
=
1.323
 
(0.201 x 2)
+
(0.198 x 2)
+
(0.198 x 2)
=
2.104
 
2.104 - 1.323 = 0.781 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
  
ΔrG⦵   = ΔrH⦵ – (T298 x ΔrS⦵)   =   681.3– (298 x 0.781)  =
+448.4kJmol-1
ΔrH⦵
=
 +681.3 kJmol-1 Positive value: the reaction is endothermic
ΔrS⦵
=
 +0.781 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG⦵ 298K
=
 +448.4 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
Keq 298K
=
 2.51 x 10-79 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 872K (599°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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