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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Hydrogen + iodine in equilibrium with hydrogen iodide
           +       2
Hydrogen
 +
Iodine
  
Reactants
  
Hydrogen iodide
 
Products
  
Products – Reactants
ΔfH⦵
  
ΔfH⦵
 
Σf-reactH⦵
  
ΔfH⦵
  
 
 
Σf-prodH⦵
  
Σf-prodH⦵ - Σf-reactH⦵ = ΔrH⦵
(0.0 x 1)
+
(0.0 x 1)
=
0.00
 
(26.5 x 2)
=
53.0
 
53.0 - 0.0 = 53.0 kJmol-1
                             
S⦵
  
S⦵
 
ΣreactS⦵
  
S⦵
  
 
 
ΣprodS⦵
  
ΣprodS⦵ - ΣreactS⦵ = ΔrS⦵
(0.131 x 1)
+
(0.116 x 1)
=
0.247
 
(0.207 x 2)
=
0.413
 
0.413 - 0.247 = 0.166 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
  
ΔrG⦵   = ΔrH⦵ – (T298 x ΔrS⦵)   =   53.0– (298 x 0.166)  =
+3.4kJmol-1
ΔrH⦵
=
 +53.0 kJmol-1 Positive value: the reaction is endothermic
ΔrS⦵
=
 +0.166 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG⦵ 298K
=
 +3.4 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
Keq 298K
=
 0.255 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 318K (45°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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