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Thermochemistry: Play With Reaction Synthlet


    
   or    Kelvin        
Decomposition of calcium carbonate to CaO and CO2
           +        
Calcium carbonate
 
Reactants
 
Calcium oxide
+
Carbon dioxide
 
Products
 
Products – Reactants
ΔfH
 
 
Σf-reactH
 
ΔfH
 
ΔfH
 
 
Σf-prodH
 
Σf-prodH - Σf-reactH = ΔrH
(-1,206.9 x 1)
=
-1,206.90
 
(-635.1 x 1)
+
(-393.5 x 1)
=
-1,028.6
 
-1,028.6 - -1,206.9 = 178.3 kJmol-1
                             
S
 
 
ΣreactS
 
S
 
S
 
 
ΣprodS
 
ΣprodS - ΣreactS = ΔrS
(0.093 x 1)
=
0.093
 
(0.040 x 1)
+
(0.214 x 1)
=
0.253
 
0.253 - 0.093 = 0.161 kJK-1mol-1
Gibbs free energy at 298K (standard conditions and standard temperature):
 
ΔrG   = ΔrH – (T298 x ΔrS)   =   178.3– (298 x 0.161)  =
+130.4kJmol-1
ΔrH
=
+178.3 kJmol-1 Positive value: the reaction is endothermic
ΔrS
=
+0.161 kJK-1mol-1 Positive value: the system becomes more dispersed
ΔrG 298K
=
+130.4 kJmol-1 Positive value: the reaction is not feasible (spontaneous)
Keq 298K
=
1.37 x 10-23 Value is less than 1: the reaction proceeds to the left
ΔG° = 0.0, and the system is at equilibrium, at a temperature of 1,110K (837°C)

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List Thermochemical Reactions Build-a-Reaction Synthlet

© Mark R. Leach 1999 –


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