Surface Science: Foundations of Catalysis and Nanoscience
Chapter 4. Thermodynamics & Kinetics of Surface Processes: Supplemental Material
Here's a link to a page written by Catherine Stampfl on
Surface Thermodynamics and Kinetics.
Here is a link to on-line
Surface Science tutorials.
The NIST Thermophysical Properties Division
is one of the oldest data research centers in the United States. For over 60 years, it has produced a great number of the
periodical compilations and electronic databases that have become a major source of recommended data for scientific research
and industrial process design, for both pure materials and mixtures.
The NIST Chemistry WebBook
provides access to data compiled and distributed by NIST under the Standard Reference Data Program.
Questions and Exercises
- Calculate the flux of N_{2} onto a surface at 1.45 x 10^{-4} Pa and T = 300 K. If this is striking a Pt(111) surface, what is the flux in the equivalent of ML s^{-1}?
- Calculate the flux of benzene onto a surface at 2.50 x 10^{-6} Pa and T = 298 K. If this is striking a Re(0001) surface, what is the flux in the equivalent of ML s^{-1}?
- The enthalpy of adsorption of C_{2}H_{6} on Pt(111) is -36.8 kJ mol^{-1}. Assuming that the Langmuir model of adsorption holds, calculate the equilibrium coverage in m^{-2} and fractional coverage in ML for p = 2.00 x 10^{-3} Pa and T = 140 K.
- Calculate the chemical potential of the adsorbed layer for the conditions of Exercise 3.
- What is a compensation effect?
- Does a large value of pre-exponential factor for desorption correspond to a favorable or unfavorable
entropy change for reaching the transition state?
- How is the common unit of exposure defined and what is its significance?
- What assumptions are made in the Langmuir model of molecular adsorption?
- Give a plausible explanation of how dissociative adsorption can exhibit a sticking coefficient that falls off more
slowly than .
- Why does the enthalpy of desorption of physisorbed multilayers tend asymptotically to the enthalpy of sublimation?
- Is the peak temperature in TPD determined by the enthalpy of adsorption?
- How do the peak temperatures in TPD change as a function of initial coverage for first and second order desorption?
- If a mechanism predicts first order kinetics and first order kinetics is observed for the reaction,
is this sufficient evidence to prove the mechanism is an accurate description of the reaction?
If the reaction kinetics are not first order, does this prove that the mechanism is incorrect?
- If a Ni(100) surface is exposed to 5 x 10^{-4} Pa of CO at 300 K, how long does it take to reach theta = 0.1 ML, 0.5 ML and 1.0 ML for (a) s = 0.9 (constant), and (b) s_{0} = 0.9 but following Langmuir kinetics.
- Define all fractional coverages with respect to surface atom density. All values are for T = 400 K on Rh(111). H_{2} adsorbs dissociatively following Langmuir kinetics with an initial sticking coefficient of 0.90. CO adsorbs molecularly following precursor mediated kinetics with s_{0} = 0.85. Calculate the initial rate of adsorption in molecules m^{-2} s^{-1} of CO if p_{CO} = 1.25 x 10^{-4} Pa. Calculate the rate of adsorption in ML s^{-1} of H(a) from H_{2} adsorption if the H_{2} pressure is 1.25 x 10^{-4} Pa and the coverage is 0.25 ML.
- The following equilibrium coverage data have been acquired for the adsorption of CO on Ni(100) with the system at T = 100 K. The sticking coefficient is found not to depend on T.
(a) Determine the enthalpy of adsorption and the activation energies for adsorption and desorption given that the pre-exponential factor for desorption is A = 1 x 10^{12} s^{-1} and sigma_{0} = 1.61 x 10^{19} m^{-2}. (b) What error would result in E_{des} if the "normal" pre-exponential factor of A = 1 x 10^{13} s^{-1} were to be assumed?
p/Pa |
1x10^{-5} |
5x10^{-5} |
10x10^{-5} |
50x10^{-5} |
100x10^{-5} |
sigma/m^{2} |
5.55x10^{17} |
24.4x10^{17} |
42.4x10^{17} |
103x10^{17} |
126x10^{17} |
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