Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

10.2 Kinetics of heterogeneous reactions (surface reactions) 221
I
Determination of V , V ∞ , and the adsorption enthalpy ∆H : At a series
of temperatures , we need to measure Θ ( )= ( )
∞ ( ) as function of by
pressure/volume measurements in an ultrahigh vacuum apparatus.
• From Eq. 10.42:
• Multiplication of l.h.s. and r.h.s. with
• Aplotof
=
1
Θ =
∞
=1+ 1
1
∞
:
∞
+
∞
(10.44)
= + (10.45)
vs. gives a straight line (see the inset in Fig. 10.4) with slope
=( ∞
) −1 (10.46)
and intercept
=( ∞
) −1 (10.47)
•
• van’t Hoff plot:
=
slope
intercept =
ln
(1 ) = −∆
(10.48)
(10.49)
I Desorption rate: If ∆ 0 0 we can describe the desorption rate by TST (see Figs.
10.3 und 10.6).
−1 = µ
‡
exp − ∆
0
(10.50)
The ’s are partition functions per unit area.