Chapter 12, Problem 82E

The decomposition of NH₃ to N₂ and H₂ was studied on two surfaces:

Surface	Ea (kJ/mol)
W	163
Os	197

Without a catalyst, the activation energy is 335 kJ/mol.

a. Which surface is the better heterogeneous catalyst for the decomposition of NH₃? Why?

b. How many times faster is the reaction at 298 K on the W surface compared with the reaction with no catalyst present? Assume that the frequency factor A is the same for each reaction.

c. The decomposition reaction on the two surfaces obeys a rate law of the form

$\text{Rate}\text{=}k\frac{\left[{\text{NH}}_3\right]}{\left[{\text{H}}_2\right]}$

How can you explain the inverse dependence of the rate on the H₂ concentration?