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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Oxidation of nitrogen to nitric oxide
           +       2
Nitrogen
+
Oxygen
 
Reactants
 
Nitric oxide
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(0.0 x 1)
+
(0.0 x 1)
=
0.00
 
(90.3 x 2)
=
180.5
 
180.5 - 0.0 = 180.5 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.192 x 1)
+
(0.205 x 1)
=
0.397
 
(0.211 x 2)
=
0.422
 
0.422 - 0.397 = 0.025 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   180.5– (298 x 0.025)  =
+173.1kJmol-1
ΔrH
=
+180.5 kJmol-1 Positive value: the reaction is endothermic
ΔrS
=
+0.025 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG 298K
=
+173.1 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
Keq 298K
=
4.53 x 10-31 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 7,287K (7,014°C)

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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –


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