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List Thermochemical Reactions Build-a-Reaction Synthlet

Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Cracking butane to ethylene and hydrogen
     2       +        
Butane
 
Reactants
 
Ethylene
+
Hydrogen
 
Products
 
Products – Reactants
Δf H ⦵
 
 
Σf-react H ⦵
 
Δf H ⦵
 
ΔfH
 
 
Σf-prod H ⦵
 
Σf-prod H ⦵ - Σf-react H ⦵ = Δr H ⦵
(-126.2 x 1)
=
-126.15
 
(52.3 x 2)
+
(0.0 x 1)
=
104.5
 
104.5 - -126.2 = 230.7 kJmol-1
                             
S ⦵
 
 
Σreact S ⦵
 
S ⦵
 
S
 
 
Σprod S ⦵
 
Σprod S ⦵ - Σreact S ⦵ = Δr S ⦵
(0.310 x 1)
=
0.310
 
(0.220 x 2)
+
(0.131 x 1)
=
0.570
 
0.570 - 0.310 = 0.260 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
Δr G ⦵   = Δr H ⦵ – (T 298 x Δr S ⦵)   =   230.7– (298 x0.260)  =
+153.3kJmol-1
Δr H ⦵
=
 +230.7 kJmol-1 Positive value: the reaction is endothermic
Δr S ⦵
=
 +0.260 kJK-1mol-1 Positive value: the system becomes more dispersed
Δr G ⦵ 298K
=
 +153.3 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
K eq 298K
=
 1.34 x 10-27 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 889K (616°C)
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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –

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