Consider the decomposition of NH3 (g).

Question

2 NH3 (g) → N2 (g) + 3 H2 (g)
The reaction is catalyzed on a surface of either tungsten or osmium. The activation energies for the catalyzed and uncatalyzed reactions are given below.
W Ea = 163 kJ/mol
Os Ea = 197 kJ/mol
No catalyst Ea = 335 kJ/mol

(a) Which surface is a better catalyst for the decomposition of NH3?
(b) Assuming a temperature of 298 K, how many times faster is the reaction on the W surface compared to when the reaction is uncatalyzed?
(c) The reaction is first order in NH3 at low concentrations of NH3 but ultimately becomes 0 order in NH3 as the concentration of NH3 is increased. Provide an explanation for this observation.

Answer 1

a.
The one with the lowest Ea.

b.
k = -Ea/RT. Do that for uncatalyzed.
Do that for W surface.
Compare the k values.