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List Thermochemical Reactions Build-a-Reaction Synthlet

Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Dimerising methane to acetylene and hydrogen
    2       +         3
Methane
 
Reactants
 
Acetylene
+
Hydrogen
 
Products
 
Products – Reactants
Δf H ⦵
 
 
Σf-react H ⦵
 
Δf H ⦵
 
ΔfH
 
 
Σf-prod H ⦵
 
Σf-prod H ⦵ - Σf-react H ⦵ = Δr H ⦵
(-74.8 x 2)
=
-149.62
 
(226.7 x 1)
+
(0.0 x 3)
=
226.7
 
226.7 - -149.6 = 376.4 kJmol-1
                             
S ⦵
 
 
Σreact S ⦵
 
S ⦵
 
S
 
 
Σprod S ⦵
 
Σprod S ⦵ - Σreact S ⦵ = Δr S ⦵
(0.186 x 2)
=
0.373
 
(0.201 x 1)
+
(0.131 x 3)
=
0.593
 
0.593 - 0.373 = 0.220 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
Δr G ⦵   = Δr H ⦵ – (T 298 x Δr S ⦵)   =   376.4– (298 x0.220)  =
+310.7kJmol-1
Δr H ⦵
=
 +376.4 kJmol-1 Positive value: the reaction is endothermic
Δr S ⦵
=
 +0.220 kJK-1mol-1 Positive value: the system becomes more dispersed
Δr G ⦵ 298K
=
 +310.7 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
K eq 298K
=
 3.54 x 10-55 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 1,707K (1,434°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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