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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Oxidation of ammonia to nitrogen with hydrogen peroxide
    2       +       3       +         6
Ammonia, aqueous
+
Hydrogen peroxide
 
Reactants
 
Nitrogen
+
Water
 
Products
 
Products – Reactants
ΔfH
 
ΔfH
 
Σf-reactH
 
ΔfH
 
ΔfH
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(-80.3 x 2)
+
(-187.8 x 3)
=
-723.92
 
(0.0 x 1)
+
(-285.8 x 6)
=
-1,715.0
 
-1,715.0 - -723.9 = -991.1 kJmol-1
                             
S
 
S
 
ΣreactS
 
S
 
S
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.111 x 2)
+
(0.110 x 3)
=
0.551
 
(0.192 x 1)
+
(0.070 x 6)
=
0.611
 
0.611 - 0.551 = 0.060 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   -991.1– (298 x 0.060)  =
-1,008.8kJmol-1
ΔrH
=
-991.1 kJmol-1 Negative value: the reaction is exothermic
ΔrS
=
+0.060 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG 298K
=
-1,008.8 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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