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List Thermochemical Reactions Build-a-Reaction Synthlet

Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Hydrogenation of benzene
           +       3
Benzene
+
Hydrogen
 
Reactants
 
Cyclohexane
 
Products
 
Products – Reactants
Δf H ⦵
 
ΔfH⦵
 
Σf-react H ⦵
 
Δf H ⦵
 
 
 
Σf-prod H ⦵
 
Σf-prod H ⦵ - Σf-react H ⦵ = Δr H ⦵
(49.0 x 1)
+
(0.0 x 3)
=
49.00
 
(-37.3 x 1)
=
-37.3
 
-37.3 - 49.0 = -86.3 kJmol-1
                             
S ⦵
 
S⦵
 
Σreact S ⦵
 
S ⦵
 
 
 
Σprod S ⦵
 
Σprod S ⦵ - Σreact S ⦵ = Δr S ⦵
(0.173 x 1)
+
(0.131 x 3)
=
0.565
 
(0.204 x 1)
=
0.204
 
0.204 - 0.565 = -0.361 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
Δr G ⦵   = Δr H ⦵ – (T 298 x Δr S ⦵)   =   -86.3– (298 x-0.361)  =
+21.3kJmol-1
Δr H ⦵
=
 -86.3 kJmol-1 Negative value: the reaction is exothermic
Δr S ⦵
=
 -0.361 kJK-1mol-1 Negative value: the system becomes less dispersed
Δr G ⦵ 298K
=
 +21.3 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
K eq 298K
=
 1.85 x 10-4 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 239K (-34°C)
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© Mark R. Leach 1999 –

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