Decomposition of ammonia on platinum surface

To interpret the kinetics of the decomposition of ammonia on a hot platinum wire. 

In an experiment at 1348 C with no added hydrogen, Schwab and Schmidt (Z. physikal. Chem. B 1929,3,344) observed the values for the pressure p, as a. function of the time of reaction t, given in table 2. 

From the experiments at 1138 C we see that the rate of reaction is approximately inversely proportional to the pressure of the added hydrogen. This suggests that the surface is largely covered ( poisoned ) by hydrogen. Since the addition of nitrogen has no effect on the rate, we may safely neglect any adsorption of nitrogen. 

If we use -p to denote partial pressure and 6 fraction of surface occupied and we use the subscripts H for hydrogen and A for ammonia, then according to Langmuir s theory 

If then the rate is proportional to the firaction of surface covered by ammonia we shall expect the rate, under the above conditions (3), to be directly proportional to pA and inversely proportional to Pb- We have then 

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