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List Thermochemical Reactions Build-a-Reaction Synthlet

Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Formation of methane from its elements
           +       2
Carbon
+
Hydrogen
 
Reactants
 
Methane
 
Products
 
Products – Reactants
Δf H ⦵
 
ΔfH⦵
 
Σf-react H ⦵
 
Δf H ⦵
 
 
 
Σf-prod H ⦵
 
Σf-prod H ⦵ - Σf-react H ⦵ = Δr H ⦵
(0.0 x 1)
+
(0.0 x 2)
=
0.00
 
(-74.8 x 1)
=
-74.8
 
-74.8 - 0.0 = -74.8 kJmol-1
                             
S ⦵
 
S⦵
 
Σreact S ⦵
 
S ⦵
 
 
 
Σprod S ⦵
 
Σprod S ⦵ - Σreact S ⦵ = Δr S ⦵
(0.006 x 1)
+
(0.131 x 2)
=
0.267
 
(0.186 x 1)
=
0.186
 
0.186 - 0.267 = -0.081 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
Δr G ⦵   = Δr H ⦵ – (T 298 x Δr S ⦵)   =   -74.8– (298 x-0.081)  =
-50.7kJmol-1
Δr H ⦵
=
 -74.8 kJmol-1 Negative value: the reaction is exothermic
Δr S ⦵
=
 -0.081 kJK-1mol-1 Negative value: the system becomes less dispersed
Δr G ⦵ 298K
=
 -50.7 kJmol-1 Negative value: the reaction is feasible (spontaneous)
K eq 298K
=
 7.76 x 108 Value is greater than 1: the reaction proceeds to the right
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 925K (652°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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