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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Formation of methane from its elements
           +       2
Carbon
+
Hydrogen
 
Reactants
 
Methane
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(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
 
ΣreactS
 
S
 
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(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):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   -74.8– (298 x -0.081)  =
-50.7kJmol-1
ΔrH
=
-74.8 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
-0.081 kJK-1mol-1 Negative value: the system becomes less dispersed
ΔrG 298K
=
-50.7 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 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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