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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Hydrogenation to ethylene to ethane
           +      
Ethylene
+
Hydrogen
 
Reactants
 
Ethane
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(52.3 x 1)
+
(0.0 x 1)
=
52.26
 
(-84.7 x 1)
=
-84.7
 
-84.7 - 52.3 = -136.9 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.220 x 1)
+
(0.131 x 1)
=
0.350
 
(0.230 x 1)
=
0.230
 
0.230 - 0.350 = -0.121 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   -136.9– (298 x -0.121)  =
-101.0kJmol-1
ΔrH
=
-136.9 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
-0.121 kJK-1mol-1 Negative value: the system becomes less dispersed
ΔrG 298K
=
-101.0 kJmol-1 Negative value: the reaction is feasible (spontaneous)
Keq 298K
=
5.03 x 10+17 Value is greater than 1: the reaction proceeds to the right
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 1,135K (862°C)

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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –


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