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List Thermochemical Reactions Build-a-Reaction Synthlet

Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Reduction of iron(III) oxide with hydrogen
           +       3 2       +         3
Iron(III) oxide
+
Hydrogen
 
Reactants
 
Iron
+
Steam
 
Products
 
Products – Reactants
Δf H ⦵
 
ΔfH⦵
 
Σf-react H ⦵
 
Δf H ⦵
 
ΔfH
 
 
Σf-prod H ⦵
 
Σf-prod H ⦵ - Σf-react H ⦵ = Δr H ⦵
(-824.2 x 1)
+
(0.0 x 3)
=
-824.20
 
(0.0 x 2)
+
(-241.8 x 3)
=
-725.5
 
-725.5 - -824.2 = 98.7 kJmol-1
                             
S ⦵
 
S⦵
 
Σreact S ⦵
 
S ⦵
 
S
 
 
Σprod S ⦵
 
Σprod S ⦵ - Σreact S ⦵ = Δr S ⦵
(0.087 x 1)
+
(0.131 x 3)
=
0.479
 
(0.027 x 2)
+
(0.189 x 3)
=
0.621
 
0.621 - 0.479 = 0.142 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
Δr G ⦵   = Δr H ⦵ – (T 298 x Δr S ⦵)   =   98.7– (298 x0.142)  =
+56.5kJmol-1
Δr H ⦵
=
 +98.7 kJmol-1 Positive value: the reaction is endothermic
Δr S ⦵
=
 +0.142 kJK-1mol-1 Positive value: the system becomes more dispersed
Δr G ⦵ 298K
=
 +56.5 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
K eq 298K
=
 1.23 x 10-10 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 697K (424°C)
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© Mark R. Leach 1999 –

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