Under the approprate conditions, NO forms N2O and NO2: 3 NO(g) <-----> N2O(g) +
ID: 793291 • Letter: U
Question
Under the approprate conditions, NO forms N2O and NO2:
3 NO(g) <-----> N2O(g) + NO2(g)
Use the values for delta G for the following reactions to calculate the value of Kp for the above reaction at 500.0 C.
2NO(g) + O2(g) <-----> 2NO2(g) delta G = -69.7 kJ
2N2O(g) <-----> 2NO(g) + N2(g) delta G = -33.8 kJ
N2(g) + O2 (g) <------>2NO(g) delta G = 173.2 kJ
Kp = _______
Explanation / Answer
Actually, you know you have to use deltaG = -RT ln(Kc), and then calculate Kp from Kc and the ideal gas law PV = nRT --> n/V = P/RT. You have to combine the rxns that you're given to get the rxn that you want:
(1) 2NO(g)+O2(g) = 2NO2(g) dG= -69700J ; let's try and eliminate O2 from the overall rxn
(2) 2NO(g) = N2(g)+O2(g) dG= -173200J
- - - - - - - - - - - - - - - - - - - -
(3) 4NO(g) = 2NO2(g) + N2(g) dG= -69700J -173200J; now eliminate N2 if you can
(4) 2NO(g)+N2(g) = 2N2O(g) dG= +33800J
- - - - - - - - - - - - - - - - - - - -
(5) 6NO(g) = 2NO2(g) + 2N2O(g) dG= -69700J -173200J + 33800J
Tidy up a bit:
3NO(g) = NO2(g) + N2O(g) dG= (-69700J -173200J + 33800J)/2
Kc = [NO2] [N2O] / [NO]^3 = (pNO2/RT) (pN2O/RT) / (pNO/RT)^3
= Kp / RT
deltaG = -RT ln(Kc)
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