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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Combustion of butane to carbon dioxide and steam
    2       +       13 8       +         10
Butane
+
Oxygen
 
Reactants
 
Carbon dioxide
+
Steam
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
ΔfH
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(-126.2 x 2)
+
(0.0 x 13)
=
-252.30
 
(-393.5 x 8)
+
(-241.8 x 10)
=
-5,566.3
 
-5,566.3 - -252.3 = -5,314.0 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
S
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.310 x 2)
+
(0.205 x 13)
=
3.287
 
(0.214 x 8)
+
(0.189 x 10)
=
3.598
 
3.598 - 3.287 = 0.311 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   -5,314.0– (298 x 0.311)  =
-5,406.6kJmol-1
ΔrH
=
-5,314.0 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
+0.311 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG 298K
=
-5,406.6 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
>10100 Value is greater than 1: the reaction proceeds to the right
No equilibrium temperature: this reaction is feasible at all temperatures

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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –


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