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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Combustion of methane to carbon dioxide and steam
           +       2       +         2
Methane
+
Oxygen
 
Reactants
 
Carbon dioxide
+
Steam
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
ΔfH
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(-74.8 x 1)
+
(0.0 x 2)
=
-74.81
 
(-393.5 x 1)
+
(-241.8 x 2)
=
-877.2
 
-877.2 - -74.8 = -802.3 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
S
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.186 x 1)
+
(0.205 x 2)
=
0.597
 
(0.214 x 1)
+
(0.189 x 2)
=
0.591
 
0.591 - 0.597 = -0.005 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   -802.3– (298 x -0.005)  =
-800.8kJmol-1
ΔrH
=
-802.3 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
-0.005 kJK-1mol-1 Negative value: the system becomes less dispersed
ΔrG 298K
=
-800.8 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
>10100 Value is greater than 1: the reaction proceeds to the right
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 156,097K (155,824°C)

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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –


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