Page 112 - Modeling of Chemical Kinetics and Reactor Design

82 Modeling of Chemical Kinetics and Reactor Design

Solution

N + 3H → 2NH 3
2
2
or

1 2
N + H → NH 3
2
2
3 3
Calculate the heat of reaction at the reference temperature using the
heats of formation.

∆H o T ( ) = 2 ∆H o − 3 ∆H o − ∆H o
rxnT R F NH 3 F H 2 F N 2

The heats of formation of the elements H , N are zero at 298 K.
2
2
Therefore,
∆H ( K) = 2(–11,020) kcal/kmol
o
rxn 298
kcal
,
= −22 040 reacted.
kmol N 2
The minus sign shows that the heat of reaction is exothermic.

Component a b × 10 –3 c × 10 –6
N (g) 6.457 1.39 –0.069
2
H (g) 6.946 –0.196 0.476
2
NH (g) 5.92 8.963 –1.764
3
∆ –15.455 17.124 –4.887
Substituting ∆H ( K) and the parameters ∆a, ∆b, and ∆c in
o
rxn 298
Equation 2-110 gives

∆a T T ) + (
2
2
∆H rxnT T ( )= ∆H o rxnT T ( )+ ( − R ∆b T − )
T
R
R
2
+ ( T − )
∆c
3
3
T R
3